Some of the hardest problems a Java Developer will ever have to face are classpath errors: ClassNotFoundException, NoClassDefFoundError, Jar Hell, Xerces Hell and company. In this post we will go through the root causes of these problems, and see how a minimal tool (JHades) can help solving them quickly. We will see why Maven cannot (always) prevent classpath duplicates, and also: The only way to deal with Jar Hell Class loaders The Class loader chain Class loader priority: Parent First vs Parent Last Debugging server startup problems Making sense of Jar Hell with jHades Simple strategy for avoiding classpath problems The classpath gets fixed in Java 9? The only way to deal with Jar Hell Classpath problems can be time-consuming to debug, and tend to happen at the worst possible times and places: before releases, and often in environments where there is little to no access by the development team. They can also happen at the IDE level, and become a source of reduced productivity. We developers tend to find these problems early and often, and this is the usual response: Let's try to save us some hair and get to the bottom of this. These type of problems are hard to approach via trial and error. The only real way to solve them is to really understand what is going on, but where to start? It turns out that Jar Hell problems are simpler than what they look, and only a few concepts are needed to solve them. In the end, the common root causes for Jar Hell problems are: a Jar is missing there is one Jar too many a class is not visible where it should be But if it's that simple, then why are classpath problems so hard to debug? Jar Hell stack traces are incomplete One reason is that the stack traces for classpath problems have a lot of information missing that is needed to troubleshoot the problem. Take for example this stack trace: java.lang.IncompatibleClassChangeError: Class org.jhades.SomeServiceImpl does not implement the requested interfaceorg.jhades.SomeService org.jhades.TestServlet.doGet(TestServlet.java:19) It says that a class does not implement a certain interface. But if we look at the class source: publicclassSomeServiceImpl implementsSomeService { @Override publicvoiddoSomething() { System.out.println( "Call successful!"); } Well, the class clearly implements the missing interface! So what is going on then? The problem is that the stack trace is missing a lot of information that is critical to understanding the problem. The stack trace should have probably contained an error message such as this (we will learn what this means): The Class SomeServiceImpl of class loader /path/to/tomcat/lib does not implement the interface SomeService loaded from class loader Tomcat - WebApp - /path/to/tomcat/webapps/test This would be at least an indication of where to start: Someone new learning Java would at least know that there is this notion of class loader that is essential to understand what is going on It would make clear that one class involved was not being loaded from a WAR, but somehow from some directory on the server (SomeServiceImpl). What is a Class Loader? To start, a Class Loader is just a Java class, more exactly an instance of a class at runtime. It is NOT an inaccessible internal component of the JVM like for example the garbage collector. Take for example the WebAppClassLoader of Tomcat, here is it's javadoc. As you can see it's just a plain Java class, we can even write our own class loader if needed. Any subclass of ClassLoader will qualify as a class loader. The main responsibilities of a class loader is to known where class files are located, and then load classes on JVM demand. Everything is linked to a class loader Each object in the JVM is linked to it's Class via getClass(), and each class is linked to a class loader via getClassLoader(). This means that: Every object in the JVM is linked to a class loader! Let's see how this fact can be used to troubleshoot a classpath error scenario. How-To find where a class file really is Let's take an object and see where it's class file is located in the file system: System.out.println(service.getClass() .getClassLoader() .getResource("org/jhades/SomeServiceImpl.class")); This is the full path to the class file: jar:file:/Users/user1/.m2/repository/org/jhades/jar-2/1.0-SNAPSHOT/jar-2-1.0-SNAPSHOT.jar!/org/jhades/SomeServiceImpl.class As we can see the class loader is just a runtime component that knowns where in the file system to look for class files and how to load them. But what happens if the class loader cannot find a given class? The Class loader Chain By default in the JVM, if a class loader does not find a class, it will then ask it's parent class loader for that same class and so forth. This continues all the way up until the JVM bootstrap class loader (more on this later). This chain of class loaders is the class loader delegation chain. Class loader priority: Parent First vs Parent Last Some class loaders delegate requests immediately to the parent class loader, without searching first in their own known set of directories for the class file. A class loader operating on this mode is said to be in Parent First mode. If a class loader first looks for a class locally and only after queries the parent if the class is not found, then that class loader is said to be working in Parent Last mode. Do all applications have a class loader chain ? Even the most simple Hello World main method has 3 class loaders: The Application class loader, responsible for loading the application classes (parent first) The Extensions class loader, that loads jars from $JAVA_HOME/jre/lib/ext (parent first) The Bootstrap class loader, that loads any class shipped with the JDK such as java.lang.String (no parent class loader) What does the class loader chain of a WAR application look like? In the case of application servers like Tomcat or Websphere, the class loader chain is configured differently than a simple Hello World main method program. Take for example the case of the Tomcat class loader chain: Here we wee that each WAR runs in a WebAppClassLoader, that works in parent last mode (it can be set to parent first as well). The Common class loader loads libraries installed at the level of the server. What does the Servlet spec say about class loading? Only a small part of the class loader chain behavior is defined by the Servlet container specification: The WAR application runs on it's own application class loader, that might be shared with other applications or not The files in WEB-INF/classes take precedence over everything else After that, it's anyones guess! The rest is completely open for interpretation by container providers. Why isn't there a common approach for class loading across vendors? Usually open source containers like Tomcat or Jetty are configured by default to look for classes in the WAR first, and only then search in server class loaders. This allows for applications to use their own versions of libraries that override the ones available on the server. What about the big iron servers? Commercial products like Websphere will try to 'sell' you their own server provided libraries, that by default take precedence over the ones installed on the WAR. This is done assuming that if you bought the server you want also to use the JEE libraries and versions it provides, which is often NOT the case. This makes deploying to certain commercial products a huge hassle, as they behave differently then the Tomcat or Jetty that developers use to run applications in their workstation. We will see further on a solution for this. Common Problem: duplicate class versions At this moment you probably have a huge question: What if there are two jars inside a WAR that contain the exact same class? The answer is that the behavior is undetermined and only at runtime one of the two classes will be chosen. Which one gets chosen depends on the internal implementation of the class loader, there is no way to know upfront. But luckily most projects these days use Maven, and Maven solves this problem by ensuring only one version of a given jar is added to the WAR. So a Maven project is immune to this particular type of Jar Hell, right? Why Maven does not prevent classpath duplicates Unfortunately Maven cannot help in all Jar Hell situations. In fact, many Maven projects that don't use certain quality control plugins can have hundreds of duplicate class files on the classpath (I saw trunks with over 500 duplicates). There are several reasons for that: Library publishers occasionally change the artifact name of a jar: This happens due to re-branding or other reasons. Take for example the example of the JAXB jar. There is no way Maven can identify those artifacts as being the same jar! Some jars are published with and without dependencies: Some library providers provide a 'with dependencies' version of a jar, which includes other jars inside. If we have transitive dependencies with the two versions, we will end up with duplicates. Some classes are copied between jars: Some library creators, when faced with the need for a certain class will just grab it from another project and copy it to a new jar without changing the package name. Are all class files duplicates dangerous? If the duplicate class files exist inside the same class loader, and the two duplicate class files are exactly identical then it does not matter which one gets chosen first - this situation is not dangerous. If the two class files are inside the same class loader and they are not identical, then there is no way which one will be chosen at runtime - this is problematic and can manifest itself when deploying to different environments. If the class files are in two different class loaders, then they are never considered identical (see the class identity crisis section further on). How can WAR classpath duplicates be avoided? This problem can be avoided for example by using the Maven Enforcer Plugin, with the extra rule of Ban Duplicate Classes turned on. You can quickly check if your WAR is clean using the JHades WAR duplicate classes report as well. This tool has an option to filter 'harmless' duplicates (same class file size). But even a clean WAR might have deployment problems: Classes missing, classes taken from the server instead of the WAR and thus with the wrong version, class cast exceptions, etc. Debugging the classpath with JHades Classpath problems often show up when the application server is starting up, which is a particularly bad moment specially when deploying to an environment where there is limited access. JHades is a tool to help deal it with Jar Hell (disclaimer: I wrote it). It's a single Jar with no dependencies other than the JDK7 itself. This is an example of how to use it: newJHades() .printClassLoaders() .printClasspath() .overlappingJarsReport() .multipleClassVersionsReport() .findClassByName("org.jhades.SomeServiceImpl") This prints to the screen the class loader chain, jars, duplicate classes, etc. Debugging server startup problems JHades works works well in scenarios where the server does not start properly. A servlet listener is provided that allows to print classpath debugging information even before any other component of the application starts running. ClassCastException and the Class Identity Crisis When troubleshooting Jar Hell, beware of ClassCastExceptions. A class is identified in the JVM not only by it's fully qualified class name, but also by it's class loader. This is counterintuitive but in hindsight makes sense: We can create two different classes with the same package and name, ship them in two jars and put them in two different class loaders. One let's say extends ArrayList and the other is a Map. The classes are therefore completely different (despite the same name) and cannot be cast to each other! The runtime will throw a CCE to prevent this potential error case, because there is no guarantee that the classes are castable. Adding the class loader to the class identifier was the outcome of the Class Identity Crisis that occurred in earlier Java days. A Strategy for Avoiding Classpath Problems This is easier said then done, but the best way to avoid classpath related deployment problems is to run the production server in Parent Last mode. This way the class versions of the WAR take precedence over the ones on the server, and the same classes are used in production and in a developer workstation where it's likely that Tomcat, Jetty or other open source Parent Last server is being used. In certain servers like Websphere, this is not sufficient and you also have to provide special properties on the manifest file to explicitly turn off certain libraries like for example JAX-WS. Fixing the classpath in Java 9 In Java 9 the classpath gets completely revamped with the new Jigsaw modularity system. In Java 9 a jar can be declared as a module and it will run in it's own isolated class loader, that reads class files from other similar module class loaders in an OSGI sort of way. This will allow multiple versions of the same Jar to coexist in the same application if needed. Conclusions In the end, Jar Hell problems are not that low level or unapproachable as they might seem at first. It's all about zip files (jars) being present/ not being present in certain directories, how to find those directories, and how to debug the classpath in environments with limited access. By knowing a limited set of concepts such as Class Loaders, the Class Loader Chain and Parent First / Parent Last modes, these problems can be tackled effectively. External links This presentation Do you really get class loaders from Jevgeni Kabanov of ZeroTurnaround (JRebel company) is a great resource about Jar Hell and the different type of classpath related exceptions.

Originally written by Fernando Laudares The need to have multiple instances of MySQL (the well-known mysqld process) running in the same server concurrently in a transparent way, instead of having them executed in separate containers/virtual machines, is not very common. Yet from time to time the Percona Support team receives a request from a customer to assist in the configuration of such an environment. MySQL provides a tool to facilitate the execution of multiple instances called mysqld_multi: “mysqld_multi is designed to manage several mysqld processes that listen for connections on different Unix socket files and TCP/IP ports. It can start or stop servers, or report their current status.” For tests and development purposes, MySQL Sandbox might be more practical and I personally prefer to use it for my own tests. Both tools work around launching and managing multiple mysqld processes but Sandbox has, as the name suggests, a “sandbox” approach, making it easy to both create and dispose a new instance (including all data inside it). It is more usual to see mysqld_multi being used in production servers: It’s provided with the server package and uses the same single configuration file that people are used to look for when setting up MySQL. So, how does it work? How do we configure and manage the instances? And as importantly, how do we backup all the instances we create? Understanding the concept of groups in my.cnf You may have noticed already that MySQL’s main configuration file (or “option file“), my.cnf, is arranged under what is called group structures: Sections defining configuration options specific to a given program or purpose. Usually, the program itself gives name to the group, which appears enclosed by brackets. Here’s a basic my.cnf showing three such groups: [client] port= 3306 socket= /var/run/mysqld/mysqld.sock user = john password = p455w0rd [mysqld] user= mysql pid-file= /var/run/mysqld/mysqld.pid socket= /var/run/mysqld/mysqld.sock port= 3306 datadir= /var/lib/mysql [xtrabackup] target_dir = /backups/mysql/ The options defined in the group [client] above are used by the mysql command-line tool. As such, if you don’t specify any other option when executing mysql it will attempt to connect to the local MySQL server through the socket in /var/run/mysqld/mysqld.sock and using the credentials stated in that group. Similarly, mysqld will look for the options defined under its section at startup, and the same happens with Percona XtraBackup when you run a backup with that tool. However, the operating parameters defined by the above groups may also be stated as command-line options during the execution of the program, in which case they they replace the ones defined in my.cnf. Getting started with multiple instances To have multiple instances of MySQL running we must replace the [mysqld] group in the my.cnf configuration file by as many [mysqlN] groups as we want instances running, with “N” being a positive integer, also called option group number. This number is used by mysqld_multi to identify each instance, so it must be unique across the server. Apart from the distinct group name, the same options that are valid for [mysqld] applies on [mysqldN] groups, the difference being that while stating them is optional for [mysqld] (it’s possible to start MySQL with an empty my.cnf as default values are used if not explicitly provided) some of them (like socket, port, pid-file, and datadir) are mandatory when defining multiple instances – so they don’t step on each other’s feet. Here’s a simple modified my.cnf showing the original [mysqld] group plus two other instances: [mysqld] user= mysql pid-file= /var/run/mysqld/mysqld.pid socket= /var/run/mysqld/mysqld.sock port= 3306 datadir= /var/lib/mysql [mysqld1] user= mysql pid-file= /var/run/mysqld/mysqld1.pid socket= /var/run/mysqld/mysqld1.sock port= 3307 datadir= /data/mysql/mysql1 [mysqld7] user= mysql pid-file= /var/run/mysqld/mysqld7.pid socket= /var/run/mysqld/mysqld7.sock port= 3308 datadir= /data/mysql/mysql7 Besides using different pid files, ports and sockets for the new instances I’ve also defined a different datadir for each – it’s very important that the instances do not share the same datadir. Chances are you’re importing the data from a backup but if that’s not the case you can simply use mysql_install_db to create each additional datadir (but make sure the parent directory exists and that the mysql user has write access on it): mysql_install_db --user=mysql --datadir=/data/mysql/mysql7 Note that if /data/mysql/mysql7 doesn’t exist and you start this instance anyway then myqld_multi will call mysqld_install_db itself to have the datadir created and the system tables installed inside it. Alternatively from restoring a backup or having a new datadir created you can make a physical copy of the existing one from the main instance – just make sure to stop it first with a clean shutdown, so any pending changes are flushed to disk first. Now, you may have noted I wrote above that you need to replace your original MySQL instance group ([mysqld]) by one with an option group number ([mysqlN]). That’s not entirely true, as they can co-exist in harmony. However, the usual start/stop script used to manage MySQL won’t work with the additional instances, nor mysqld_multi really manages [mysqld]. The simple solution here is to have the group [mysqld] renamed with a suffix integer, say [mysqld0] (you don’t need to make any changes to it’s current options though), and let mysqld_multi manage all instances. Two commands you might find useful when configuring multiple instances are: $ mysqld_multi --example …which provides an example of a my.cnf file configured with multiple instances and showing the use of different options, and: $ my_print_defaults --defaults-file=/etc/my.cnf mysqld7 …which shows how a given group (“mysqld7″ in the example above) was defined within my.cnf. Managing multiple instances mysqld_multi allows you to start, stop, reload (which is effectively a restart) and report the current status of a given instance, all instances or a subset of them. The most important observation here is that the “stop” action is managed through mysqladmin – and internally that happens on an individual basis, with one “mysqladmin … stop” call per instance, even if you have mysqld_multi stop all of them. For this to work properly you need to setup a MySQL account with the SHUTDOWN privilege and defined with the same user name and password in all instances. Yes, it will work out of the box if you run mysqld_multi as root in a freshly installed server where the root user can access MySQL passwordless in all instances. But as the manual suggests, it’s better to have an specific account created for this purpose: mysql> GRANT SHUTDOWN ON *.* TO 'multi_admin'@'localhost' IDENTIFIED BY 'multipass'; mysql> FLUSH PRIVILEGES; If you plan on replicating the datadir of the main server across your other instances you can have that account created before you make copies of it, otherwise you just need to connect to each instance and create a similar account (remember, the privileged account is only needed by mysqld_multi to stop the instances, not to start them). There’s a special group that can be used on my.cnf to define options for mysqld_multi, which should be used to store these credentials. You might also indicate in there the path for the mysqladmin and mysqld (or mysqld_safe) binaries to use, though you might have a specific mysqld binary defined for each instance inside it’s respective group. Here’s one example: [mysqld_multi] mysqld = /usr/bin/mysqld_safe mysqladmin = /usr/bin/mysqladmin user = multi_admin password = multipass You can use mysqld_multi to start, stop, restart or report the status of a particular instance, all instances or a subset of them. Here’s a few examples that speak for themselves: $ mysqld_multi report Reporting MySQL (Percona Server) servers MySQL (Percona Server) from group: mysqld0 is not running MySQL (Percona Server) from group: mysqld1 is not running MySQL (Percona Server) from group: mysqld7 is not running $ mysqld_multi start $ mysqld_multi report Reporting MySQL (Percona Server) servers MySQL (Percona Server) from group: mysqld0 is running MySQL (Percona Server) from group: mysqld1 is running MySQL (Percona Server) from group: mysqld7 is running $ mysqld_multi stop 7,0 $ mysqld_multi report 7 Reporting MySQL (Percona Server) servers MySQL (Percona Server) from group: mysqld7 is not running $ mysqld_multi report Reporting MySQL (Percona Server) servers MySQL (Percona Server) from group: mysqld0 is not running MySQL (Percona Server) from group: mysqld1 is running MySQL (Percona Server) from group: mysqld7 is not running Managing the MySQL daemon What is missing here is an init script to automate the start/stop of all instances upon server initialization/shutdown; now that we use mysqld_multi to control the instances, the usual /etc/init.d/mysql won’t work anymore. But a similar startup script (though much simpler and less robust) relying on mysqld_multi is provided alongside MySQL/Percona Server, which can be found in /usr/share//mysqld_multi.server. You can simply copy it over as /etc/init.d/mysql, effectively replacing the original script while maintaining it’s name. Please note: You may need to edit it first and modify the first two lines defining “basedir” and “bindir” as this script was not designed to find out the good working values for these variables itself, which the original single-instance /etc/init.d/mysql does. Considering you probably have mysqld_multi installed in /usr/bin, setting these variables as follows is enough: basedir=/usr bindir=/usr/bin Configuring an instance with a different version of MySQL If you’re planning to have multiple instances of MySQL running concurrently chances are you want to use a mix of different versions for each of them, such as during a development cycle to test an application compatibility. This is a common use for mysqld_multi, and simple enough to achieve. To showcase its use I downloaded the latest version of MySQL 5.6 available and extracted the TAR file in /opt: $ tar -zxvf mysql-5.6.20-linux-glibc2.5-x86_64.tar.gz -C /opt Then I made a cold copy of the datadir from one of the existing instances to /data/mysql/mysqld574: $ mysqld_multi stop 0 $ cp -r /data/mysql/mysql1 /data/mysql/mysql5620 $ chown mysql:mysql -R /data/mysql/mysql5620 and added a new group to my.cnf as follows: [mysqld5620] user = mysql pid-file = /var/run/mysqld/mysqld5620.pid socket = /var/run/mysqld/mysqld5620.sock port = 3309 datadir = /data/mysql/mysql5620 basedir = /opt/mysql-5.6.20-linux-glibc2.5-x86_64 mysqld = /opt/mysql-5.6.20-linux-glibc2.5-x86_64/bin/mysqld_safe Note the use of basedir, pointing to the path were the binaries for MySQL 5.6.20 were extracted, as well as an specific mysqld to be used with this instance. If you have made a copy of the datadir from an instance running a previous version of MySQL/Percona Server you will need to consider the same approach use when upgrading and run mysql_upgrade. * I did try to use the latest experimental release of MySQL 5.7 (mysql-5.7.4-m14-linux-glibc2.5-x86_64.tar.gz) but it crashed with: *** glibc detected *** bin/mysqld: double free or corruption (!prev): 0x0000000003627650 *** Using the conventional tools to start and stop an instance Even though mysqld_multi makes things easier to control in general let’s not forget it is a wrapper; you can still rely (though not always, as shown below) on the conventional tools directly to start and stop an instance: mysqld* and mysqladmin. Just make sure to use the parameter –defaults-group-suffix to identify which instance you want to start: mysqld --defaults-group-suffix=5620 and –socket to indicate the one you want to stop: $mysqladmin -S /var/run/mysqld/mysqld5620.sock shutdown * However, mysqld won’t work to start an instance if you have redefined the option ‘mysqld’ on the configuration group, as I did for [mysqld5620] above, stating: [ERROR] mysqld: unknown variable 'mysqld=/opt/mysql-5.6.20-linux-glibc2.5-x86_64/bin/mysqld_safe' I’ve tested using “ledir” to indicate the path to the directory containing the binaries for MySQL 5.6.20 instead of “mysqld” but it also failed with a similar error. If nothing else, that shows you need to stick with mysqld_multi when starting instances in a mixed-version environment. Backups The backup of multiple instances must be done in an individual basis, like you would if each instance was located in a different server. You just need to provide the appropriate parameters to identify the instance you’re targeting. For example, we can simply use socket with mysqldump when running it locally: $ mysqldump --socket=/var/run/mysqld/mysqld7.sock --all-databases > mysqld7.sql In Percona XtraBackup there’s an option named –defaults-group that should be used in environments running multiple instances to indicate which one you want to backup : $ innobackupex --defaults-file=/etc/my.cnf --defaults-group=mysqld7 --socket=/var/run/mysqld/mysqld7.sock /root/Backup/ Yes, you also need to provide a path to the socket (when running the command locally), even though that information is already available in “–defaults-group=mysqld7″; as it turns out, only the Percona XtraBackup tool (which is called by innobackupex during the backup process) makes use of the information available in the group option. You may need to provide credentials as well (“–user” & “–password”), and don’t forget you’ll need to prepare the backup afterwards. The option “defaults-group” is not available in all versions of Percona XtraBackup so make sure to use the latest one. Summary Running multiple instances of MySQL concurrently in the same server transparently and without any contextualization or a virtualization layer is possible with both mysqld_multi and MySQL Sandbox. We have been using the later at Percona Support to quickly spin on new disposable instances (though you might as easily keep them running indefinitely). In this post though I’ve looked at mysqld_multi, which is provided with MySQL server and remains the official solution for providing an environment with multiple instances. The key aspect when configuring multiple instances in my.cnf is the notion of group name option, as you replace a single [mysqld] section by as many [mysqldN] sections as you want instances running. It’s important though to pay attention to certain details when defining the options for each one of these groups, specially when mixing instances from different MySQL/Percona Server versions. Differently from MySQL Sandbox, where each instance relies on it’s own configuration file, you should be careful each time you edit the shared my.cnf file as a syntax error when configuring a single group option will prevent all instances from starting upon the server’s (re)initialization. I hope to have covered the major points about mysqld_multi here but feel free to leave us a note below if you have something else to add or any comment to contribute.

Learn Fibonacci Series patterns and best practices with easy Java 8 source code examples in this outstanding tutorial by Pierre-Yves Saumont

we write service apis which cater to certain business logic. there are few cross-cutting concerns that cover all service apis like security, logging, auditing, measuring latencies and so on. this is a repetitive non-business code which can be reused among other methods. one way to reuse is to move these repetitive code into its own methods and invoke them in the service apis somethings like: public class myservice{ public servicemodel service1(){ isauthorized(); //execute business logic. } } public class myanotherservice{ public servicemodel service1(){ isauthorized(): //execute business logic. } } the above approach will work but not without creating code noise, mixing cross-cutting concerns with the business logic. there is another approach to solve the above requirements which is by using aspect and this approach is called aspect oriented programming (aop). there are a different ways you can make use of aop – by using spring aop, javaee aop. in this example i will try to use aop using cdi in java ee applications. to explain this i have picked a very simple example of building a web application to fetch few records from database and display in the browser. creating the data access layer the table structure is: create table people( id int not null auto_increment, name varchar(100) not null, place varchar(100), primary key(id)); lets create a model class to hold a person information package demo.model; public class person{ private string id; private string name; private string place; public string getid(){ return id; } public string setid(string id) { this.id = id;} public string getname(){ return name; } public string setname(string name) { this.name = name;} public string getplace(){ return place; } public string setplace(string place) { this.place = place;} } lets create a data access object which exposes two methods - to fetch the details of all the people to fetch the details of one person of given id package demo.dao; import demo.common.databaseconnectionmanager; import demo.model.person; import java.sql.connection; import java.sql.preparedstatement; import java.sql.resultset; import java.sql.sqlexception; import java.sql.statement; import java.util.arraylist; import java.util.list; public class peopledao { public list getallpeople() throws sqlexception { string sql = "select * from people"; connection conn = databaseconnectionmanager.getconnection(); list people = new arraylist<>(); try (statement statement = conn.createstatement(); resultset rs = statement.executequery(sql)) { while (rs.next()) { person person = new person(); person.setid(rs.getstring("id")); person.setname(rs.getstring("name")); person.setplace(rs.getstring("place")); people.add(person); } } return people; } public person getperson(string id) throws sqlexception { string sql = "select * from people where id = ?"; connection conn = databaseconnectionmanager.getconnection(); try (preparedstatement ps = conn.preparestatement(sql)) { ps.setstring(1, id); try (resultset rs = ps.executequery()) { if (rs.next()) { person person = new person(); person.setid(rs.getstring("id")); person.setname(rs.getstring("name")); person.setplace(rs.getstring("place")); return person; } } } return null; } } you can use your own approach to get a new connection. in the above code i have created a static utility that returns me the same connection. creating interceptors creating interceptors involves 2 steps: create interceptor binding which creates an annotation annotated with @interceptorbinding that is used to bind the interceptor code and the target code which needs to be intercepted. create a class annotated with @interceptor which contains the interceptor code. it would contain methods annotated with @aroundinvoke , different lifecycle annotations, @aroundtimeout and others. lets create an interceptor binding by name @latencylogger package demo; import java.lang.annotation.target; import java.lang.annotation.retention; import static java.lang.annotation.retentionpolicy.*; import static java.lang.annotation.elementtype.*; import javax.interceptor.interceptorbinding; @interceptorbinding 10 @retention(runtime) 11 @target({method, type}) public @interface latencylogger { } now we need to create the interceptor code which is annotated with @interceptor and also annotated with the interceptor binding we created above i.e @latencylogger : package demo; import java.io.serializable; import javax.interceptor.aroundinvoke; import javax.interceptor.interceptor; import javax.interceptor.invocationcontext; @interceptor @latencylogger public class latencyloggerinterceptor implements serializable{ @aroundinvoke public object computelatency(invocationcontext invocationctx) throws exception{ long starttime = system.currenttimemillis(); //execute the intercepted method and store the return value object returnvalue = invocationctx.proceed(); long endtime = system.currenttimemillis(); system.out.println("latency of " + invocationctx.getmethod().getname() +": " + (endtime-starttime)+"ms"); return returnvalue; } } there are two interesting things in the above code: use of @aroundinvoke parameter of type invocationcontext passed to the method @aroundinvoke designates the method as an interceptor method. an interceptor class can have only one method annotated with this annotation. when ever a target method is intercepted, its context is passed to the interceptor. using the invocationcontext one can get the method details, the parameters passed to the method. we need to declare the above interceptor in the web-inf/beans.xml file demo.latencyloggerinterceptor creating service apis annotated with interceptors we have already created the interceptor binding and the interceptor which gets executed. now lets create the service apis and then annotate them with the interceptor binding /* * to change this license header, choose license headers in project properties. * to change this template file, choose tools | templates * and open the template in the editor. */ package demo.service; import demo.latencylogger; import demo.dao.peopledao; import demo.model.person; import java.sql.sqlexception; import java.util.list; import javax.inject.inject; public class peopleservice { @inject peopledao peopledao; @latencylogger public list getallpeople() throws sqlexception { return peopledao.getallpeople(); } @latencylogger public person getperson(string id) throws sqlexception { return peopledao.getperson(id); } } we have annotated the service methods with the interceptor binding @latencylogger . the other way would be to annotate at the class level which would then apply the annotation to all the methods of the class. another thing to notice is the @inject annotation that injects the instance i.e injects the dependency into the class. next is to wire up the controller and view to show the data. the controller is the servlet and view is a plain jsp using jstl tags. /* * to change this license header, choose license headers in project properties. * to change this template file, choose tools | templates * and open the template in the editor. */ package demo; import demo.model.person; import demo.service.peopleservice; import java.io.ioexception; import java.sql.sqlexception; import java.util.list; import java.util.logging.level; import java.util.logging.logger; import javax.inject.inject; import javax.servlet.servletexception; import javax.servlet.annotation.webservlet; import javax.servlet.http.httpservlet; import javax.servlet.http.httpservletrequest; import javax.servlet.http.httpservletresponse; @webservlet(name = "aopdemo", urlpatterns = {"/aopdemo"}) public class aopdemoservlet extends httpservlet { @inject peopleservice peopleservice; @override public void doget(httpservletrequest request, httpservletresponse response) throws servletexception, ioexception { try { list people = peopleservice.getallpeople(); person person = peopleservice.getperson("2"); request.setattribute("people", people); request.setattribute("person", person); getservletcontext().getrequestdispatcher("/index.jsp").forward(request, response); } catch (sqlexception ex) { logger.getlogger(aopdemoservlet.class.getname()).log(level.severe, null, ex); } } } the above servlet is available at http://localhost:8080/ /aopdemo. it fetches the data and redirects to the view to display the same. note that the service has also been injected using @inject annotation. if the dependencies are not injected and instead created using new then the interceptors will not work. this is an important point which i realised while building this sample. the jsp to render the data would be hello world! idnameplace details for person with id=2 with this you would have built a very simple app using interceptors. thanks for reading and staying with me till this end. please share your queries/feedback as comments. and also share this article among your friends

Here's how to create a persistence configuration in the Java SE environment.

Creating a method that has many parameters is a major sin. Whenever there is need to create such a method, sniff in the air: it is code smell. Harden your unit tests and then refactor. No excuse, no buts. Refactor! Use builder pattern or even better use Fluent API. For the latter the annotation processor fluflu may be of great help. Having all that said we may come to a point in our life when we face real life and not the idealistic pattern that we can follow in our hobby projects. There comes the legacy enterprise library monster that has the method of thousands parameters and you do not have the authority, time, courage or interest (bad for you) to modify … ops… refactor it. You could create a builder as a facade that hides the ugly API behind it if you had the time. Creating a builder is still code that you have to unit test even before you write (you know: TDD) and you just may not have the time. The code that calls the monstrous method is also there already, you just maintain it. You can still do some little trick. It may not be perfect, but still something. Assume that there is a method public void monster(String contactName, String contactId, String street, String district, ... Long pT){ ... } The first thing is to select your local variables at the location of the caller wisely. Pity the names are already chosen and you may not want to change it. There can be some reason for that, for example there is an application wide naming convention followed that may make sense even if not your style. So the call monster(nm, "05300" + dI, getStrt(), d, ... , z+g % 3L ); is not exactly what I was talking about. That is what you have and you can live with it, or just insert new variables into the code: String contactName = nm; String contactId = "05300" + dI; String street = getStrt(); Street district = d; ... Long pT = z+g % 3L; monster(contactName, contactId, street, district, ... ,pT ); or you can even write it in a way that is not usual in Java, though perfectly legal: String contactName, contactId, street, district; ... Long pT; monster(contactName = nm, contactId = "05300" + dI, street = getStrt(), district = d, ... ,pT = z+g % 3L ); Tasty is it? Depends. I would not argue on taste. If you do not like that, there is an alternative way. You can define auxiliary and very simple static methods: static T contactName(T t){ return T;} static T contactId(T t){ return T;} static T street(T t){ return T;} static T district(T t){ return T;} ... static T pT(T t){ return T;} monster(contactName(nm), contactId("05300" + dI), street(getStrt()(, district(d), ... ,pT(z+g % 3L) ); The code is still ugly but a bit more readable at the place of the caller. You can even collect static methods into a utility class, or to an interface in case of Java 8 named like with, using, to and so on. You can statically import them to your code and have some method call as nice as doSomething(using(someParameter), with(someOtherParameter), to(resultStore)); When all that is there you can feel honky dory if you answer the final question: what the blessed whatever* is parameter pT. (* “whatever” you can replace with some other words, whichever you like)

Apparently writing a URL shortener service is the new "Hello, world!" in the IoT/microservice/era world. It all started with A URL shortener service in 45 lines of Scala - neat piece of Scala, flavoured with Spray and Redis for storage. This was quickly followed with A url shortener service in 35 lines of Clojure and even URL Shortener in 43 lines of Haskell. So my inner anti-hipster asked: how long would it be in Java? But not plain Java, for goodness' sake. Spring Boot with Spring Data Redis are a good starting point. All we need is a simple controller handling GET and POST: import com.google.common.hash.Hashing; import org.apache.commons.validator.routines.UrlValidator; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.boot.SpringApplication; import org.springframework.data.redis.core.StringRedisTemplate; import org.springframework.http.*; import org.springframework.web.bind.annotation.*; import javax.servlet.http.*; import java.nio.charset.StandardCharsets; @org.springframework.boot.autoconfigure.EnableAutoConfiguration @org.springframework.stereotype.Controller public class UrlShortener { public static void main(String[] args) { SpringApplication.run(UrlShortener.class, args); } @Autowired private StringRedisTemplate redis; @RequestMapping(value = "/{id}", method = RequestMethod.GET) public void redirect(@PathVariable String id, HttpServletResponse resp) throws Exception { final String url = redis.opsForValue().get(id); if (url != null) resp.sendRedirect(url); else resp.sendError(HttpServletResponse.SC_NOT_FOUND); } @RequestMapping(method = RequestMethod.POST) public ResponseEntity save(HttpServletRequest req) { final String queryParams = (req.getQueryString() != null) ? "?" + req.getQueryString() : ""; final String url = (req.getRequestURI() + queryParams).substring(1); final UrlValidator urlValidator = new UrlValidator(new String[]{"http", "https"}); if (urlValidator.isValid(url)) { final String id = Hashing.murmur3_32().hashString(url, StandardCharsets.UTF_8).toString(); redis.opsForValue().set(id, url); return new ResponseEntity<>("http://mydomain.com/" + id, HttpStatus.OK); } else return new ResponseEntity<>(HttpStatus.BAD_REQUEST); } } The code is nicely self-descriptive and is functionally equivalent to a version in Scala. I didn't try to it squeeze too much to keep line count as short as possible, code above is quite typical with few details: I don't normally use wildcard imports I don't use fully qualified class names (I wanted to save one import line, I admit) I surround if/else blocks with braces I almost never use field injection, ugliest brother in inversion of control family. Instead I would go for constructor to allow testing with mocked Redis: private final StringRedisTemplate redis; @Autowired public UrlShortener(StringRedisTemplate redis) { this.redis = redis; } The thing I struggled the most was... obtaining the original, full URL. Basically I needed everything after .com or port. No bloody way (neither servlets, nor Spring MVC), hence the awkward getQueryString() fiddling. You can use the service as follows - creating shorter URL: $ curl -vX POST localhost:8080/https://www.google.pl/search?q=tomasz+nurkiewicz > POST /https://www.google.pl/search?q=tomasz+nurkiewicz HTTP/1.1 > User-Agent: curl/7.30.0 > Host: localhost:8080 > Accept: */* > < HTTP/1.1 200 OK < Server: Apache-Coyote/1.1 < Content-Type: text/plain;charset=ISO-8859-1 < Content-Length: 28 < Date: Sat, 23 Aug 2014 20:47:40 GMT < http://mydomain.com/50784f51 Redirecting through shorter URL: $ curl -v localhost:8080/50784f51 > GET /50784f51 HTTP/1.1 > User-Agent: curl/7.30.0 > Host: localhost:8080 > Accept: */* > < HTTP/1.1 302 Found < Server: Apache-Coyote/1.1 < Location: https://www.google.pl/search?q=tomasz+nurkiewicz < Content-Length: 0 < Date: Sat, 23 Aug 2014 20:48:00 GMT < For completeness, here is a build file in Gradle (maven would work as well), skipped in all previous solutions: buildscript { repositories { mavenLocal() maven { url "http://repo.spring.io/libs-snapshot" } mavenCentral() } dependencies { classpath 'org.springframework.boot:spring-boot-gradle-plugin:1.1.5.RELEASE' } } apply plugin: 'java' apply plugin: 'spring-boot' sourceCompatibility = '1.8' repositories { mavenLocal() maven { url 'http://repository.codehaus.org' } maven { url 'http://repo.spring.io/milestone' } mavenCentral() } dependencies { compile "org.springframework.boot:spring-boot-starter-web:1.1.5.RELEASE" compile "org.springframework.boot:spring-boot-starter-redis:1.1.5.RELEASE" compile 'com.google.guava:guava:17.0' compile 'org.apache.commons:commons-lang3:3.3.2' compile 'commons-validator:commons-validator:1.4.0' compile 'org.apache.tomcat.embed:tomcat-embed-el:8.0.9' compile "org.aspectj:aspectjrt:1.8.1" runtime "cglib:cglib-nodep:3.1" } tasks.withType(GroovyCompile) { groovyOptions.optimizationOptions.indy = true } task wrapper(type: Wrapper) { gradleVersion = '2.0' } Actually also 42 lines... That's the whole application, no XML, no descriptors, not setup. I don't treat this exercise as just a dummy code golf for shortest, most obfuscated working code. URL shortener web service with Redis back-end is an interesting showcase of syntax and capabilities of a given language and ecosystem. Much more entertaining then a bunch of algorithmic problems, e.g. found in Rosetta code. Also it's a good bare minimum template for writing a REST service. One important feature of original Scala implementation, that was somehow silently forgotten in all implementations, including this one, is that it's non-blocking. Both HTTP and Redis access is event-driven (reactive, all right, I said it), thus I suppose it can handle tens of thousands of clients simultaneously. This can't be achieved with blocking controllers backed by Tomcat. But still you have to admit such a service written in Java (not even Java 8!) is surprisingly concise, easy to follow and straightforward - none of the other solutions are that readable (this is of course subjective). Waiting for others!

javascript object notation (json) is fast becoming the de facto standard or format for transferring, sharing and passing around data. be it on the web, rest service, a remote procedure call or even an ajax request. json is light weight with little memory footprint when compared to an xml. the content of a json string in its raw form when observed looks gibberish. to make the content usable it needs to be deserialized or converted to a useable form usually a java object (pojo) or an array or list of objects depending on the json content. a typical json string is as shown below {"city":"jos","country":"nigeria","housenumber":"13","lga":"jos south", "state":"plateau","streetname":"jonah jann","village":"bukuru","ward":"1"} there are a lot of frameworks for deserializing json to a java object such as json-rpc , gson , flexjson and a whole lots of other open source libraries. of all the libraries mentioned i would in this blog post demonstrate how to use google-gson library to deserialize a json string to a java object. you can download the gson library from https://code.google.com/p/google-gson/ . to have the json string deserialized, a java object must be created that has the same fields names with the fields in the json string. there is a website that provides a service for viewing the content of a json string in a tree like manner. http://jsonviewer.stack.hu paste the json string in the text tab and view the fields and the content from the viewer tab i would deserialize a json string that contains address details to an address pojo, the address object follows the structure as seen from the json tree view above. public class address{ private string city; private string country; private string housenumber; private string lga; private string state; private string streetname; private string village; private string ward; public string getcity() { return city; } public void setcity(string city) { this.city = city; } public string getcountry() { return country; } public void setcountry(string country) { this.country = country; } public string gethousenumber() { return housenumber; } public void sethousenumber(string housenumber) { this.housenumber = housenumber; } public string getlga() { return lga; } public void setlga(string lga) { this.lga = lga; } public string getstate() { return state; } public void setstate(string state) { this.state = state; } public string getstreetname() { return streetname; } public void setstreetname(string streetname) { this.streetname = streetname; } public string getvillage() { return village; } public void setvillage(string village) { this.village = village; } public string getward() { return ward; } public void setward(string ward) { this.ward = ward; } @override public string tostring() { return "address [city=" + city + ", country=" + country + ", housenumber=" + housenumber + ", lga=" + lga + ", state=" + state + ", streetname=" + streetname + ", village=" + village + ", ward=" + ward + "]"; } } to perform the deserialization with gson is easy, create pojo classes to hold your data, import the packages com.google.gson.gson and com.google.gson.gsonbuilder, to your project. then create and instance of the gson class and then perform the deserialization as shown below. gson gson = new gsonbuilder().create(); address address=gson.fromjson(json, address.class); voila, you have your json deserialized! the source code listing is below. package jsondeserializer import com.google.gson.gson; import com.google.gson.gsonbuilder; public class tester { public static void main(string[] args) { string json ="{\"city\":\"jos\",\"country\":\"nigeria\",\"housenumber\":\"13\",\"lga\":\"jos south\",\n" + "\"state\":\"plateau\",\"streetname\":\"jonah jann\",\"village\":\"bukuru\",\"ward\":\"1\"}"; gson gson = new gsonbuilder().create(); address address=gson.fromjson(json, address.class); system.out.println(address.tostring()); } }

By Alex Komyagin, Technical Services Engineer at MongoDB Setting up Kerberos authentication and SSL encryption in a MongoDB Java application is not as simple as other languages. In this post, I’m going to show you how to create a Kerberos and SSL enabled Java application that communicates with MongoDB. My original setup consists of the following: 1) KDC server: kdc.mongotest.com kerberos config file (/etc/krb5.conf): [logging] default = FILE:/var/log/krb5libs.log kdc = FILE:/var/log/krb5kdc.log admin_server = FILE:/var/log/kadmind.log [libdefaults] default_realm = MONGOTEST.COM dns_lookup_realm = false dns_lookup_kdc = false ticket_lifetime = 24h renew_lifetime = 7d forwardable = true [realms] MONGOTEST.COM = { kdc = kdc.mongotest.com admin_server = kdc.mongotest.com } [domain_realm] .mongotest.com = MONGOTEST.COM mongotest.com = MONGOTEST.COM KDC has the following principals: [email protected] - user principle (for java app) mongodb/[email protected] - service principle (for mongodb server) 2) MongoDB server: rhel64.mongotest.com MongoDB version: 2.6.0 MongoDB config file: dbpath= logpath= fork=true auth = true setParameter = authenticationMechanisms=GSSAPI sslOnNormalPorts = true sslPEMKeyFile = /etc/ssl/mongodb.pem This server also has the global environment variable $KRB5_KTNAME set to the keytab file exported from KDC. Application user is configured in the admin database like this: { "_id" : "[email protected]", "user" : "[email protected]", "db" : "$external", "credentials" : { "external" : true }, "roles" : [ { "role" : "readWrite", "db" : "test" } ] } Download the Java driver: wget http://central.maven.org/maven2/org/mongodb/mongo-java-driver/2.12.1/mongo-java-driver-2.12.1.jar Install java and jdk: sudo yum install java-1.7.0 sudo yum install java-1.7.0-devel Create a certificate store for Java and store the server certificate there, so that Java knows who it should trust: keytool -importcert -file mongodb.crt -alias mongoCert -keystore firstTrustStore (mongodb.crt is just a public certificate part of mongodb.pem) Copy kerberos config file to the application server: /etc/krb5.conf or ““C:\WINDOWS\krb5.ini“` (otherwise you’ll have to specify kdc and realm as Java runtime options) Use kinit to store the principal password on the application server: kinit [email protected] As an alternative to kinit, you can use JAAS to cache kerberos credentials. Compile and run the Java program javac -cp ../mongo-java-driver-2.12.1.jar SSLApp.java java -cp .:../mongo-java-driver-2.12.1.jar -Djavax.net.ssl.trustStore=firstTrustStore -Djavax.net.ssl.trustStorePassword=changeme -Djavax.security.auth.useSubjectCredsOnly=false SSLApp It is important to specify useSubjectCredsOnly=false, otherwise you’ll get the “No valid credentials provided (Mechanism level: Failed to find any Kerberos tgt)” exception from Java. As we discovered, this is not strictly necessary in all cases, but it is if you are relying on kinit to get the service ticket. The Java driver needs to construct MongoDB service principal name in order to request the Kerberos ticket. The service principal is constructed based on the server name you provide (unless you explicitly asked to canonicalize server name). For example, if I change rhel64.mongotest.com to the host IP address in the connection URI, I would be getting Kerberos exceptions No valid credentials provided (Mechanism level: Server not found in Kerberos database (7) - UNKNOWN_SERVER)]. So be sure you specify the same server host name as you used in the Kerberos principal (). Adding -Dsun.security.krb5.debug=true to Java runtime options helps a lot in debugging kerberos auth issues. These steps should help simplify the process of connecting Java applications with SSL. Before deploying any application with MongoDB, be sure to read through our Security Checklist which outlines recommended security measures to protect your MongoDB installation. More information on configuring MongoDB Security can be found in the MongoDB Manual. For further questions, feel free to reach out to the MongoDB team through google-groups.

the following exception occurred while hitting the url: org.apache.http.client.clientprotocolexception w/system.err(1276): at org.apache.http.impl.client.abstracthttpclient.execute(abstracthttpclient.java:557) w/system.err(1276): at org.apache.http.impl.client.abstracthttpclient.execute(abstracthttpclient.java:487) w/system.err(1276): at com.loopj.android.http.asynchttprequest.makerequest(asynchttprequest.java:78) w/system.err(1276): at com.loopj.android.http.asynchttprequest.makerequestwithretries(asynchttprequest.java:102) w/system.err(1276): at com.loopj.android.http.asynchttprequest.run(asynchttprequest.java:58) w/system.err(1276): at java.util.concurrent.executors$runnableadapter.call(executors.java:390) w/system.err(1276): at java.util.concurrent.futuretask.run(futuretask.java:234) w/system.err(1276): at java.util.concurrent.threadpoolexecutor.runworker(threadpoolexecutor.java:1080) w/system.err(1276): at java.util.concurrent.threadpoolexecutor$worker.run(threadpoolexecutor.java:573) w/system.err(1276): at java.lang.thread.run(thread.java:841) w/system.err(1276): caused by: org.apache.http.client.circularredirectexception: circular redirect to 'redirecturi' w/system.err(1276): at org.apache.http.impl.client.defaultredirecthandler.getlocationuri(defaultredirecthandler.java:173) w/system.err(1276): at org.apache.http.impl.client.defaultrequestdirector.handleresponse(defaultrequestdirector.java:923) w/system.err(1276): at org.apache.http.impl.client.defaultrequestdirector.execute(defaultrequestdirector.java:475) w/system.err(1276): at org.apache.http.impl.client.abstracthttpclient.execute(abstracthttpclient.java:555) details / information about the exception: protocolexception: signals that an http protocol violation has occurred. for example a malformed status line or headers, a missing message body, etc. when redirecthandler determines the location request is expected to be redirected to given the response from the target server and the current request execution context. public static final string allow_circular_redirects = "http.protocol.allow-circular-redirects"; defines whether circular redirects (redirects to the same location) should be allowed. the http spec is not sufficiently clear whether circular redirects are permitted, therefore optionally they can be enabled when the redirection and the parameter of "http.protocol.allow-circular-redirects" is false it works for the first time and from the second time it throws circularredirectexception("circular redirect to '" + redirecturi + "'") we may wonder why the first time we didn't get the exception and were allowed but not the second time? let's look at getlocationuri method of defaultredirecthandler.java class, we can found the code snippet as follows. if (redirectlocations.contains(redirecturi)) { throw new circularredirectexception("circular redirect to '" + redirecturi + "'"); } else { redirectlocations.add(redirecturi); } when first time we hit, the redirectlocations object is null and it will initializes redirectlocations redirectlocations = (redirectlocations) context.getattribute(redirect_locations); if (redirectlocations == null) { redirectlocations = new redirectlocations(); context.setattribute(redirect_locations, redirectlocations); } so, the redirecturi wont be available in the redirectlocations object. when we hit the second time, the redirecturi is existing in the redirectlocations object. so, the apache throwing circularredirectexception. solutions: here we have 2 solutions, either one of them we can use. 1. gethttpclient().getparams().setparameter(clientpnames.allow_circular_redirects, true); 2. extend defaultredirecthandler and modify getlocationuri method.

Hello, how are you? Today we will talk about situations in which the use of the JPA/Hibernate is not recommended. Which alternatives do we have outside the JPA world? What we will talk about: JPA/Hibernate problems Solutions to some of the JPA/Hibernate problems Criteria for choosing the frameworks described here Spring JDBC Template MyBatis Sormula sql2o Take a look at: jOOQ and Avaje Is a raw JDBC approach worth it? How can I choose the right framework? Final thoughts I have created 4 CRUDs in my github using the frameworks mentioned in this post, you will find the URL at the beginning of each page. I am not a radical that thinks that JPA is worthless, but I do believe that we need to choose the right framework for the each situation. If you do not know I wrote a JPA book (in Portuguese only) and I do not think that JPA is the silver bullet that will solve all the problems. I hope you like the post. [= JPA/Hibernate Problems There are times that JPA can do more harm than good. Below you will see the JPA/Hibernate problems and in the next page you will see some solutions to these problems: Composite Key: This, in my opinion, is the biggest headache of the JPA developers. When we map a composite key we are adding a huge complexity to the project when we need to persist or find a object in the database. When you use composite key several problems will might happen, and some of these problems could be implementation bugs. Legacy Database: A project that has a lot of business rules in the database can be a problem when wee need to invoke StoredProcedures or Functions. Artifact size: The artifact size will increase a lot if you are using the Hibernate implementation. The Hibernate uses a lot of dependencies that will increase the size of the generated jar/war/ear. The artifact size can be a problem if the developer needs to do a deploy in several remote servers with a low Internet band (or a slow upload). Imagine a project that in each new release it is necessary to update 10 customers servers across the country. Problems with slow upload, corrupted file and loss of Internet can happen making the dev/ops team to lose more time. Generated SQL: One of the JPA advantages is the database portability, but to use this portability advantage you need to use the JPQL/HQL language. This advantage can became a disadvantage when the generated query has a poor performance and it does not use the table index that was created to optimize the queries. Complex Query: That are projects that has several queries with a high level of complexity using database resources like: SUM, MAX, MIN, COUNT, HAVING, etc. If you combine those resources the JPA performance might drop and not use the table indexes, or you will not be able to use a specific database resource that could solve this problem. Framework complexity: To create a CRUD with JPA is very simples, but problems will appear when we start to use entities relationships, inheritance, cache, PersistenceUnit manipulation, PersistenceContext with several entities, etc. A development team without a developer with a good JPA experience will lose a lot of time with JPA ‘rules‘. Slow processing and a lot of RAM memory occupied: There are moments that JPA will lose performance at report processing, inserting a lot of entities or problems with a transaction that is opened for a long time. After reading all the problems above you might be thinking: “Is JPA good in doing anything?”. JPA has a lot of advantages that will not be detailed here because this is not the post theme, JPA is a tool that is indicated for a lot of situations. Some of the JPA advantages are: database portability, save a lot of the development time, make easier to create queries, cache optimization, a huge community support, etc. In the next page we will see some solutions for the problems detailed above, the solutions could help you to avoid a huge persistence framework refactoring. We will see some tips to fix or to workaround the problems described here. Solutions to Some of the JPA/Hibernate problems We need to be careful if we are thinking about removing the JPA of our projects. I am not of the developer type that thinks that we should remove a entire framework before trying to find a solution to the problems. Some times it is better to choose a less intrusive approach. Composite Key Unfortunately there is not a good solution to this problem. If possible, avoid the creation of tables with composite key if it is not required by the business rules. I have seen developers using composite keys when a simple key could be applied, the composite key complexity was added to the project unnecessarily. Legacy Databases The newest JPA version (2.1) has support to StoredProcedures and Functions, with this new resource will be easier to communicate with the database. If a JPA version upgrade is not possible I think that JPA is not the best solution to you. You could use some of the vendor resources, e.g. Hibernate, but you will lose database and implementations portability. Artifact Size An easy solution to this problem would be to change the JPA implementation. Instead of using the Hibernate implementation you could use the Eclipsellink, OpenJPA or the Batoo. A problem might appear if the project is using Hibernate annotation/resources; the implementation change will require some code refactoring. Generated SQL and Complexes Query The solution to these problems would be a resource named NativeQuery. With this resource you could have a simplified query or optimized SQL, but you will sacrifice the database portability. You could put your queries in a file, something like SEARCH_STUDENTS_ORACLE or SEARCH_STUDENTS_MYSQL, and in production environment the correct file would be accessed. The problem of this approach is that the same query must be written for every database. If we need to edit the SEARCH_STUDENTS query, it would be required to edit the oracle and mysql files. If your project is has only one database vendor the NativeQuery resource will not be a problem. The advantage of this hybrid approach (JPQL and NativeQuery in the same project) is the possibility of using the others JPA advantages. Slow Processing and Huge Memory Size This problem can be solved with optimized queries (with NativeQuery), query pagination and small transactions. Avoid using EJB with PersistenceContext Extended, this kind of context will consume more memory and processing of the server. There is also the possibility of getting an entity from database as a “read only” entity, e.g.: entity that will only be used in a report. To recover an entity in a “read only” state is not needed to open a transaction, take a look at the code below: String query = "select uai from Student uai"; EntityManager entityManager = entityManagerFactory.createEntityManager(); TypedQuery typedQuery = entityManager.createQuery(query, Student.class); List resultList = typedQuery.getResultList(); Notice that in the code above there is no opened transaction, all the returned entities will be detached (non monitored by the JPA). If you are using EJB mark your transaction as NOT_SUPPORTED or you could use @Transactional(readOnly=true). Complexity I would say that there is only one solution to this problem: to study. It will be necessary to read books, blogs, magazines or any other trustful source of JPA material. More study is equals to less doubts in JPA. I am not a developer that believes that JPA it is the only and the best solution to every problem, but there are moments that JPA is not the best to tool to use. You must be careful when deciding about a persistence framework change, usually a lot of classes are affected and a huge refactoring is needed. Several bugs may be caused by this refactoring. It is needed to talk with the project mangers about this refactoring and list all the positive and negative effects. In the next four pages we will see 4 persistence frameworks that can be used in our projects, but before we see the frameworks I will show how that I choose each framework. Criteria for Choosing the frameworks Described Here Maybe you will think: “why the framework X is not here?”. Below I will list the criteria applied for choosing the framework displayed here: Found in more than one source of research: we can find in forums people talking about a framework, but it is harder to find the same framework appearing in more than one forum. The most quoted frameworks were chosen. Quoted by different sources: Some frameworks that we found in the forums are indicated only by its committers. Some forums does not allow “self merchandise”, but some frameworks owners still doing it. Last update 01/05/2013: I have searched for frameworks that have been updated in this past year. Quick Hello World: Some frameworks I could not do a Hello World with less than 15~20min, and with some errors. To the tutorials found in this post I have worked 7 minutes in each framework: starting counting in its download until the first database insert. The frameworks that will be displayed in here has good methods and are easy to use. To make a real CRUD scenario we have a persistence model like below: A attribute with a name different of the column name: socialSecurityNumber —-> social_security_number A date attribute a ENUM attribute With this characteristics in a class we will see some problems and how the framework solve it. Spring JDBC Template One of the most famous frameworks that we can find to access the database data is the Spring JDBC Template. The code of this project can be found in here: https://github.com/uaihebert/SpringJdbcTemplateCrud The Sprint JDBC Template uses natives queries like below: As it is possible to see in the image above the query has a database syntax (I will be using MySQL). When we use a native SQL query it is possible to use all the database resources in an easy way. We need an instance of the object JDBC Template (used to execute the queries), and to create the JDBC Template object we need to set up a datasource: We can get the datasource now (thanks to the Spring injection) and create our JDBCTemplate: PS.: All the XML code above and the JDBCTemplate instantiation could be replace by Spring injection and with a code bootstrap, just do a little research about the Spring features. One thing that I did not liked is the INSERT statement with ID recover, it is very verbose: With the KeyHolder class we can recover the generated ID in the database, unfortunately we need a huge code to do it. The other CRUD functions are easier to use, like below: Notice that to execute a SQL query it is very simple and results in a populated object, thanks to the RowMapper. The RowMapper is the engine that the JDBC Template uses to make easier to populate a class with data from the database. Take a look at the RowMapper code below: The best news about the RowMapper is that it can be used in any query of the project. The developer that is responsible to write the logic that will populate the class data. To finish this page, take a look below in the database DELETE and the database UPDATE statement: About the Spring JDBC Template we can say: Has a good support: Any search in the Internet will result in several pages with tips and bug fixes. A lot of companies use it: several projects across the world use it Be careful with different databases for the same project: The native SQL can became a problem with your project run with different databases. Several queries will need to be rewritten to adapt all the project databases. Framework Knowledge: It is good to know the Spring basics, how it can be configured and used. To those that does not know the Spring has several modules and in your project it is possible to use only the JDBC Template module. You could keep all the other modules/frameworks of your project and add only the necessary to run the JDBC Template. MyBatis MyBatis (created with the name iBatis) is a very good framework that is used by a lot of developers. Has a lot of functionalities, but we will only see a few in this post. The code of this page can be found in here: https://github.com/uaihebert/MyBatisCrud To run your project with MyBatis you will need to instantiate a Session Factory. It is very easy and the documentation says that this factory can be static: When you run a project with MyBatis you just need to instantiate the Factory one time, that is why it is in a static code. The configuration XML (mybatis.xml) it is very simple and its code can be found below: The Mapper (an attribute inside the XML above) will hold information about the project queries and how to translate the database result into Java objects. It is possible to create a Mapper in XML or Interface. Let us see below the Mapper found in the file crud_query.xml: Notice that the file is easy to understand. The first configuration found is a ResultMap that indicates the query result type, and a result class was configured “uai.model.Customer”. In the class we have a attribute with a different name of the database table column, so we need to add a configuration to the ResultMap. All queries need a ID that will be used by MyBatis session. In the beginning of the file it is possible to see a namespace declared that works as a Java package, this package will wrap all the queries and the ResultMaps found in the XML file. We could also use a Interface+Annotation instead of the XML. The Mapper found in the crud_query.xml file could be translated in to a Interface like: Only the Read methods were written in the Interface to make the code smaller, but all the CRUD methods could be written in the Interface. Let us see first how to execute a query found in the XML file: The parsing of the object is automatically and the method is easy to read. To run the query all that is needed is to use the combination “namespace + query id” that we saw in the crud_query.xml code above. If the developer wants to use the Interface approach he could do like below: With the interface query mode we have a clean code and the developer will not need to instantiate the Interface, the session class of the MyBatis will do the work. If you want to update, delete or insert a record in the database the code is very easy: About MyBatis we could say: Excellent Documentation: Every time that I had a doubt I could answer it just by reading its site documentation Flexibility: Allowing XML or Interfaces+Annotations the framework gives a huge flexibility to the developer. Notice that if you choose the Interface approach the database portability will be harder, it is easier to choose which XML to send with the deploy artifact rather than an interface Integration: Has integration with Guice and Spring Dynamic Query: Allows to create queries in Runtime, like the JPA criteria. It is possible to add “IFs” to a query to decide which attribute will be used in the query Transaction: If your project is not using Guice of Spring you will need to manually control the transaction Sormula Sormula is a ORM OpenSource framework, very similar to the JPA/Hibernate. The code of the project in this page can be found in here: https://github.com/uaihebert/SormulaCrud Sormula has a class named Database that works like the JPA EntityManagerFactory, the Database class will be like a bridge between the database and your model classes. To execute the SQL actions we will use the Table class that works like the JPA EntityManager, but the Table class is typed. To run Sormula in a code you will need to create a Database instance: To create a Database instance all that we need is a Java Connection. To read data from the database is very easy, like below: You only need to create a Database instance and a Table instance to execute all kind of SQL actions. How can we map a class attribute name different from the database table column name? Take a look below: We can use annotations to do the database mapping in our classes, very close to the JPA style. To update, delete or create data in the database you can do like below: About Sormula we can say that: Has a good documentation Easy to set up It is not found in the maven repository, it will make harder to attach the source code if needed Has a lot of checked exceptions, you will need to do a try/catch for the invoked actions sql2o This framework works with native SQL and makes easier to transform database data into Java objects. The code of the project in this page can be found in here: https://github.com/uaihebert/sql2oCrud sql2o has a Connection class that is very easy to create: Notice that we have a static Sql2o object that will work like a Connection factory. To read the database data we would do something like: Notice that we have a Native SQL written, but we have named parameters. We are not using positional parameters like ‘?1′ but we gave a name to the parameter like ‘:id’. We can say that named parameters has the advantage that we will not get lost in a query with several parameters; when we forget to pass some parameter the error message will tell us the parameter name that is missing. We can inform in the query the name of the column with a different name, there is no need to create a Mapper/RowMapper. With the return type defined in the query we will not need to instantiate manually the object, sql2o will do it for us. If you want to update, delete or insert data in the database you can do like below: It is a “very easy to use” framework. About the sql2o we can say that: Easy to handle scalar query: the returned values of SUM, COUNT functions are easy to handle Named parameters in query: Will make easy to handle SQL with a lot of parameters Binding functions: bind is a function that will automatically populate the database query parameters through a given object, unfortunately it did not work in this project for a problem with the enum. I did not investigate the problem, but I think that it is something easy to handle Take a look at: jOOQ and Avaje jOOQ jOOQ it is a framework indicated by a lot of people, the users of this frameworks praise it in a lot of sites/forums. Unfortunately the jOOQ did not work in my PC because my database was too old, and I could not download other database when writing this post (I was in an airplane). I noticed that to use the jOOQ you will need to generated several jOOQ classes based in your model. jOOQ has a good documentation in the site and it details how to generate those classes. jOOQ is free to those that uses a free database like: MySQL, Postgre, etc. The paid jOOQ version is needed to those that uses paid databases like: Oracle, SQL Server, etc. www.jooq.org/ Avaje Is a framework quoted in several blogs/forums. It works with the ORM concept and it is easy to execute database CRUD actions. Problems that I found: Not well detailed documentation: its Hello World is not very detailed Configurations: it has a required properties configuration file with a lot of configurations, really boring to those that just want to do a Hello World A Enhancer is needed: enhancement is a method do optimize the class bytecode, but is hard to setup in the beginning and is mandatory to do before the Hello World www.avaje.org Is a Raw JDBC Approach Worth It? The advantages of JDBC are: Best performance: We will not have any framework between the persistence layer and the database. We can get the best performance with a raw JDBC Control over the SQL: The written SQL is the SQL that will be executed in the database, no framework will edit/update/generate the query SQL Native Resource: We could access all natives database resources without a problem, e.g.: functions, stored procedures, hints, etc The disadvantages are: Verbose Code: After receiving the database query result we need to instantiate and populate the object manually, invoking all the required “set” methods. This code will get worse if we have classes relationships like one-to-many. It will be very easy to find a while inside another while. Fragile Code: If a database table column changes its name it will be necessary to edit all the project queries that uses this column. Some project uses constants with the column name to help with this task, e.g. Customer.NAME_COLUMN, with this approach the table column name update would be easier. If a column is removed from the database all the project queries would be updated, even if you have a column constants. Complex Portability: If your project uses more than one database it would be necessary to have almost all queries written for each vendor. For any update in any query it would be necessary to update every vendor query, this could take a lot the time from the developers. I can see only one factor that would make me choose a raw JDBC approach almost instantly: Performance: If your project need to process thousands of transactions per minutes, need to be scalable and with a low memory usage this is the best choice. Usually median/huge projects has all this high performance requirements. It is also possible to have a hybrid solution to the projects; most of the project repository (DAO) will use a framework, and just a small part of it will use JDBC I do like JDBC a lot, I have worked and I still working with it. I just ask you to not think that JDBC is the silver bullet for every problem. If you know any other advantage/disadvantage that is not listed here, just tell me and I will add here with the credits going to you. [= How Can I Choose the Right Framework? We must be careful if you want to change JPA for other project or if you are just looking for other persistence framework. If the solutions in page 3 are not solving your problems the best solution is to change the persistence framework. What should you considerate before changing the persistence framework? Documentation: is the framework well documented? Is easy to understand how it works and can it answer most of your doubts? Community: has the framework an active community of users? Has a forum? Maintenance/Fix Bugs: Is the framework receiving commits to fix bugs or receiving new features? There are fix releases being created? With which frequency? How hard is to find a developer that knows about this framework? I believe that this is the most important issue to be considered. You could add to your project the best framework in the world but without developers that know how to operate it the framework will be useless. If you need to hire a senior developer how hard would be to find one? If you urgently need to hire someone that knows that unknown framework maybe this could be very difficult. Final Thoughts I will say it again: I do not think that JPA could/should be applied to every situation in every project in the world; I do no think that that JPA is useless just because it has disadvantages just like any other framework. I do not want you to be offended if your framework was not listed here, maybe the research words that I used to find persistence frameworks did not lead me to your framework. I hope that this post might help you. If your have any double/question just post it. [= See you soon! \o_

In several recent blogs (in my reviews of the books Java EE 7 Performance Tuning and Optimization and WildFly Performance Tuning in particular), I have referenced my own past blog posts on certain Oracle JDK command-line tools. I was aghast to discover that I had never exclusively addressed the nifty jinfo tool and this post sets to rectify that troubling situation. I suspect that the reasons I chose not to write about jinfo previously include limitations related to jinfo discussed in my post VisualVM: jinfo and So Much More. In the Java SE 8 version of jinfo running on my machine, the primary limitation of jinfo on Windows that I discussed in the post Acquiring JVM Runtime Information has been addressed. In particular, I noted in that post that the -flags option was not supported on Windows version of jinfo at that time. As the next screen snapshot proves, that is no longer the case (note the use of jps to acquire the Java process ID to instruct jinfoto query). As the above screen snapshot demonstrates, the jinfo -flags command and option show the flags the explicitly specified JVM options of the Java process being monitored. If I want to find out about other JVM flags that are in effect implicitly (automatically), I can run java -XX:+PrintFlagsFinal to see all default JVM options. I can then query for any one of these against a running JVM process to find out what that particular JVM is using (same default or overridden different value). The next screen snapshot demonstrates how a small portion of the output provided from running java -XX:+PrintFlagsFinal. Let's suppose I notice a flag called PrintHeapAtGC in the above output and want to know if it's set in my particular Java application (-XX:+PrintHeapAtGC means it's set and -XX:-PrintHeapAtGC means it's not set). I can have jinfo tell me what its setting is (note my choice to use jcmd instead of jps in this case to determine the Java process ID): Because of the subtraction sign (-) instead of an addition sign (+) after the colon and before "PrintHeapAtGC", we know this is turned off for the Java process with the specified ID. It turns out that jinfo does more than let us look; it also let's us touch. The next screen snapshot shows changing this option using jinfo. As the previous screen snapshot indicates, I can turn off and on the boolean-style JVM options by simply using the same command to view the flag's setting but preceding the flag's name with the addition sign (+) to turn it on or with the substraction sign (-) to turn it off. In the example just shown, I turned off thePrintGCDateStamps, turned it back on again, and monitored its setting between those changes. Not all JVM options are boolean conditions. In those cases, their new values are assigned to them by concatenating the equals sign (=) and new value after the flag name. It's also important to note that the target JVM (the one you're trying to peek at and touch with jinfo will not allow you to change all its JVM option settings). In such cases, you'll likely see a stack trace with message "Command failed in target VM." In addition to displaying a currently running JVM's options and allowing the changing of some of these, jinfoalso allows one to see system properties used by that JVM as name/value pairs. This is demonstrated in the next screen snapshot with a small fraction of the output shown. Perhaps the easiest way to run jinfo is to simply provide no arguments other than the PID of the Java process in question and have both JVM options (non-default and command-line) and system properties displayed. Running jinfo -help provides brief usage details. Other important details are found in the Oracle documentation on the jinfo tool. These details includes the common (when it comes to these tools) reminder that this tool is "experimental and unsupported" and "might not be available in future releases of the JDK." We are also warned that jinfo on Windows requires availability of dbgeng.dll or installed Debugging Tools For Windows. Although I have referenced the handy jinfo command line tool previously in posts VisualVM: jinfo and So Much More and Acquiring JVM Runtime Information, it is a handy enough tool to justify a post of its very own. As a command-line tool, it enjoys benefits commonly associated with command-line tools such as being relatively lightweight, working well with scripts, and working in headless environments.

We’ve been missing an introduction to using MongoDB from Java for a little while now - there’s plenty of information in the documentation, but we were lacking a step-by-step guide to getting started as a Java developer. I sought to rectify this with a couple of blog posts for the MongoDB official blog: the first, an introduction to using MongoDB from Java, including a non-comprehensive list of some of the libraries you can use; the second, an introductory guide to simple CRUD operations using the Java driver: Getting Started with MongoDB and Java, Part 1 Getting Started with MongoDB and Java, Part 2 This is very much aimed at Java/JVM developers who are new to MongoDB, and want to get a feel for how you use it. These guides are for the current (2.x) driver. When we release 3.x, we’ll release updated guides as well.

[This article was written by Koby Nachmany.] If you are familiar with configuration management (aka CM) and automation, you probably know a thing or two about Puppet, and the amazing and rich collection of modules it offers. Puppet Forge contains a wealth of third party modules that enable us to do some pretty nifty stuff with almost no effort. Puppet helps deal with the messy parts of CM, like installing binaries and running installation scripts that are tedious to do manually. Tools such as Puppet were originally created for IT operations people, that are for the most part infrastructure-centric, and are best suited for setup and maintenance of hosts in a physical data center. Dealing with applications and certainly managing applications on an elastic virtualized or even cloudified environment, brings a set of new challenges despite the agility and other benefits it provides. Now imagine we can have this goodness coupled with an intelligent orchestration framework for an entire deployment? In this blog post I'd like to demonstrate how a cloud application orchestrator can complement already existing automation processes powered by configuration management tools, in this case we will demonstrate with Puppet. I will use the nodecellar application and the popular WordPress content management framework as examples. This will hopefully provide a good introduction to Cloudify blueprints. Overview So we've seen how Cloudify 3 allows us to easily orchestrate the "nodecellar" application Read about it Cloudify blueprints here. With the "nodecellar" example, Cloudify deploys a complex application using workflows that map deployment lifecycle events to bash scripts using Cloudify's bash runner plugin. Cloudify's Puppet integration now makes this pretty easy. Cloudify 3.0 - Taking Puppet to the Next Level of Orchestration. Check it out. Go The synergy between Cloudify and Puppet not only allows you to enjoy the benefits of your Puppet environment, but it also amplifies its usability by introducing unique advantages that will answer the following common challenges involved with configuration management tools: Agent Installation: Provision your service VMs, install a Puppet agent (if you like) and wires them up with the Puppet Master. Or, if you choose to run standalone, you can install the agent with the appropriate manifests needed for that service, as well. Order of Dependencies: Define the dependencies between application stacks, services and infrastructure resources. Which will then be launched based on that order. Remote Execution and Updates: Other than the basic install/uninstall, Cloudify enables customized application workflows that allow you to execute tools like remote shell scripts on a group of instances that belong to a particular service, or to a specific instance in a group. This feature is useful to run maintenance operations, such as snapshots in the case of a database, or code pushes in a continuous deployment model. In addition, you can run puppet apply whenever you feel it's right for your service. Post Deployment: Once your application is up, Cloudify will be able to glue your monitoring tool of choice, or you can choose to use the built-in one. A robust policy engine, enables auto-healing and even auto-scaling according to your service's required SLA. I'm now going to take a deep dive on my experience with a WordPress example that I feel is a very good representation of how Puppet and Cloudify work in sync. Let's say we want to deploy the popular WordPress application stack on two VMs . Something as follows: The flow is quite simple: -server 3.5.1 with the basic following modules installed: |-- hunner-wordpress (v0.6.0) |-- puppetlabs-apache (v1.0.1) - with php mods enabled |-- puppetlabs-mysql (v2.1.0) Your site.pp file should resemble something like this: node /^apache_web.*/ { include apache class { 'wordpress': create_db => false, create_db_user => false, } } node /^mysql.*/ { class { '::mysql::server': root_password => 'password', override_options => { 'mysqld' => { 'bind_address' => '0.0.0.0' } } } include mysql::client include wordpress } As we can see, we have an Apache PHP application that will likely require a database connection string (IP, port, user and password). This is where Cloudify facilitates the "gluing" of all the pieces together, by allowing us to inject dynamic/static custom facts to the dependent node (Apache server). Cloudify supports both standalone agents and PuppetMaster environments. Step 2: Tweaking the Original WordPress Module. Some minor adaptations to the wordpress init class of the WordPress module will allow us to embed these facts during Puppet agent invocation. Below is a code snippet (With defaults truncated): class wordpress ( $db_host_ip = $cloudify_related_host_ip, $db_user, = $cloudify_properties_db_user, $db_password = $cloudify_properties_db_pw, . . ) And some tweaking to the templates/wp-config.php.erb: /** MySQL hostname */ define('DB_HOST', ''); Let's add some tags for finer control of manifest execution: The MySQL node will not require the application part to run on it, so I've excluded it using a Puppet "tag" (read more about Puppet tags). Cloudify, of course, supports this and will provide the appropriate tags during agent invocation. -> class { 'wordpress::app': tag => ['postconfigure'], install_dir => $install_dir, install_url => $install_url, version => $version, db_name => $db_name, . .} Step 3: Creating the Blueprint In a similar way to the "nodecellar" blueprint, first lets create a folder with the name of "wp_puppet" and create a blueprint.yaml file within it. This file will then serve as the blueprint file. Now let's declare the name of this blueprint. blueprint: name: wp_puppet nodes: Now we can start creating the topology. Step 4: Creating VM Nodes Since, in this case I use the OpenStack provider to create the nodes, let's import the "OpenStack types" plugin. imports: - http://www.getcloudify.org/spec/openstack-plugin/1.0/plugin.yaml Since the VMs are the same, I declared a generic template for a VM host: vm_host: derived_from: cloudify.openstack.server properties: - install_agent: true - worker_config: user: ubuntu port: 22 # example for ssh key file (see `key_name` below) # this file matches the agent key configured during the bootstrap key: ~/.ssh/agent.key # Uncomment and update `management_network_name` when working a n neutron enabled openstack - management_network_name: cfy-mng-network - server: image: 8c096c29-a666-4b82-99c4-c77dc70cfb40 flavor: 102 key_name: cfy-agnt-kp security_groups: ['cfy-agent-default', 'wp_security_group'] # This is how we inject the puppet server's ip userdata: | #!/bin/bash -ex grep -q puppet /etc/hosts || echo "x.x.x.x puppet" | sudo -A tee -a /etc/hosts Create the MySQL and Apache VMs: - name: mysql_db_vm type: vm_host instances: deploy: 1 - name: apache_web_vm type: vm_host instances: deploy: 1 Step 5: Declaring Apache and MySQL Servers Since we are using the Puppet plugin to create those servers, first we have to import it: plugins: puppet_plugin: derived_from: cloudify.plugins.agent_plugin properties: url: https://github.com/cloudify-cosmo/cloudify-puppet-plugin/archive/nightly.zip The plugin defines server types as follows: middleware_server, app_server, db_server, web_server, message_bus_server, app_module. They are virtually the same, but serve the purpose of enabling better readability for the user and GUI visualization A Puppet server type is derived_from: cloudify.types.server type, but includes some puppet-specific properties and lifecycle events. For documentation see: Puppet Types So we now will go ahead and declare the server types: cloudify.types.puppet.web_server: derived_from: cloudify.types.web_server properties: # All Puppet related configuration goes inside # the "puppet_config" property. - puppet_config interfaces: cloudify.interfaces.lifecycle: # Specifically "start" operation. Otherwise tags must be # provided. - start: puppet_plugin.operations.operation cloudify.types.puppet.app_module: derived_from: cloudify.types.app_module properties: - puppet_config interfaces: cloudify.interfaces.lifecycle: - configure: puppet_plugin.operations.operation cloudify.types.puppet.db_server: derived_from: cloudify.types.db_server properties: - puppet_config interfaces: cloudify.interfaces.lifecycle: - start: puppet_plugin.operations.operation Step 6: Instantiating the Apache and MySQL nodes: Here we provide the Puppet configuration and tags and define the relationships between the nodes. Cloudify's agent will use those relationships in order to decide the appropriate facts to inject. - name: apache_web_server type: cloudify.types.puppet.web_server properties: port: 8080 puppet_config: server: puppet environment: wordpress_env relationships: - type: cloudify.relationships.contained_in target: apache_web_vm - name: wordpress_app type: cloudify.types.puppet.app_module properties: db_user: wordpress db_pass: passwd puppet_config: server: puppet tags: ['postconfigure'] environment: wordpress_env relationships: - type: cloudify.relationships.contained_in target: apache_web_server - type: wp_connected_to_mysql target: mysql_db_server - name: mysql_db_server type: cloudify.types.puppet.db_server properties: db_user: wordpress db_pass: passwd puppet_config: server: puppet environment: wordpress_env relationships: - type: cloudify.relationships.contained_in target: mysql_db_vm Step 7: Upload the Blueprint and Create the Deployment (via CLI or GUI) Then execute your deployment (via CLI or GUI). ubuntu@koby-n-cfy3-cli:~/cosmo_cli$ cfy blueprints upload -b wp9 wordpress/blueprint.yaml ubuntu@koby-n-cfy3-cli:~/cosmo_cli$ cfy deployments create -b wp9 -d WordPress_Deployment_1 Step 8: Take a Quick Coffee Break. Step 9: Enjoy your Orchestrated WordPress Stack!

There are many reasons to learn an ORM tool like JPA, but it's not a magic bullet that will solve all your problems.

the article represents steps required to configure tomcat 8 with eclipse kepler. download tomcat 8 and place it within any local folder. download eclipse java ee kepler as of date, tomcat 8 is not supported in eclipse javeee kepler. however, you could add the tomcat 8 by doing following: go to the wtp downloads page, select the latest version (currently 3.6), and download the zip. here’s the current link . copy the all of the files in features and plugins directories of the downloaded wtp into the corresponding eclipse directories in your eclipse folder (overwriting the existing files). start eclipse and click on “servers” tab in the workbench. go ahead and try adding a new server. you would find option for tomcat 8 available for selection as shown below. after clicking finish, you would see a new server added with the name as “tomcat v8.0 server at localhost”. start the server. check http://localhost:8080 (provided you installed tomcat 8 and set http port as 8080) interestingly, you would not see the welcome page, but the 404 error page. to get rid of that, double click on ”tomcat v8.0 server at localhost”. in the window that opens up, select “use tomcat installation” and, change deploy path from wtpwebapps to webapps. look at the figure below. restart the server and access http://localhost:8080 . you are all set.

One of the things that one must get used to with a new language is dealing with new conventions. Now coming from mostly a Java and Ruby background, there is a notion of constructors and constructor chaining, basically when one constructor calls another one. So when it comes to Swift, there are a few rules around the methods used to create objects. Firstly, the language guide refers to constructors as initializers. So basically anytime you want to use the term constructor, use the term initializer when you are in Swift land. More specifically, constructor chaining is known as initializer delegation. Initializers fall into two categories, Designated and Convenience.Designated initializers are the primary initializers and are responsible for initializing all properties of a class. So in this case, the only initializer here is known as the Designated one. class Person { let name: String let age: Int init(name: String, age: Int) { self.name = name self.age = age } } Now if you want to add other initializers to delegate to the Designated one, they will be known as Convenience initializers. So let's add one that defaults the age. Convenience initializers have the keyword conveniencebefore them. class Person { let name: String let age: Int init(name: String, age: Int) { self.name = name self.age = age } convenience init(name: String) { self.init(name: name, age: 100) } } Convenience initializers need to delegate to another Convenienceinitializer or a Designated initializer. Here's an example of a Convenience initializer calling another Convenienceone. class Person { let name: String let age: Int init(name: String, age: Int) { self.name = name self.age = age } convenience init(name: String) { self.init(name: name, age: 30) } convenience init() { self.init(name: "Homer") } } If you wanted to, you could create another Designated initializer. Now we have two Designated initializers and two Convenience initializers. class Person { let name: String let age: Int init(name: String, age: Int) { self.name = name self.age = age } init(age: Int, name: String) { self.age = age self.name = name } convenience init(name: String) { self.init(name: name, age: 30) } convenience init() { self.init(name: "Homer") } } What about subclasses? Once again, with initializers, there are certain rules that need to be adhered to when subclassing. So Designated initializers must call otherDesignated initializers in their immediate parent class. So let's take a look at an example. We are adding a Student class as a subclass of the Person class. It will add a property student number. class Student : Person { let number: String init(name: String, age: Int, number: String) { self.number = number super.init(name: name, age: age) } } Here we are calling the Designated initializer in the Person class. If we tried to call one of the Convenience initializers in the Person class, a compile error would occur. Also note, we need to assign the number property before calling the initializer in the parent class as it is a requirement to ensure all properties are initialized in child classes before their respective parent initializer is called. Summary Basically in summary, as explained in the language guide, Designatedinitializers delegate up and Convenience initializers delegate across. I hope this article helped in some way to improve your understanding of initializers in Swift. References Swift Language Guide

The article presents some of the frequently asked interview questions in relation with unit testing with Java code. Please suggest other questions tthat you came across and I shall include in the list below. What is unit testing? Which unit testing framework did you use? What are some of the common Java unit testing frameworks? Ans: Read the definition of Unit testing on Wikipedia page for unit testing. Simply speaking, unit testing is about testing a block of code in isolation. There are two popular unit testing framework in Java named as Junit, TestNG. In SDLC, When is the right time to start writing unit tests? Ans: Test-along if not test-driven; Writing unit tests towards end is not very effective. Test-along technique recommends developers to write the unit tests as they go with their development. With Junit 4, do we still need methods such as setUp and tearDown? Ans: No. This is taken care with help of @Before and @After annotations respectively What do following junit test annotations mean? Ans: Following is a list of frequently used JUnit 4 annotations:@Test (@Test identifies a test method) @Before (Ans: @Before method will execute before every JUnit4 test)@After (Ans: @After method will execute after every JUnit4 test)@BeforeClass (Ans: @BeforeClass method will be executed before JUnit test for a Class starts)@AfterClass (Ans: @AfterClass method will be executed after JUnit test for a Class is completed)@Ignore (@Ignore method will not be executed) How do one do exception handling unit tests using @Test annotation? Ans: @Test(expected={exception class}. For example: @Test(expected=IllegalArgumentException.class) Write a sample unit testing method for testing exception named as IndexOutOfBoundsException when working with ArrayList? @Test(expected=IndexOutOfBoundsException.class) public void outOfBounds() { new ArrayList

Ode To Code - Easily Generate Microsoft Office Files From C# "... These days, Office files are no longer in a proprietary binary format, and are we can create the files directly without using COM automation. A .docx Word file, for example, is a collection of XML documents zipped into a single file. The official name of the format is Open XML. There is an SDK to help with reading and writing OpenXML, and a Productivity Tool that can generate C# code for a given file. All you need to do is load a document, presentation, or workbook into the tool and press the “Reflect Code” button. The downside to this tool is that even a simple document will generate 4,000 lines of code. Another downside is that the generated code assumes it will write directly to the file system, however it is easy to pass in an abstract Stream object instead. So while this code isn’t perfect, the code does produce valid document and..." I've been blogging about the OpenXML SDK for years now, but I think this is the first time I've seen this part of it, this utility. And like he says, 4K LoC is like, well, allot, it does look like an awesome way to learn the low level OpenXML SDK ins and outs. Related Past Post XRef: Open Sesame - Open XML SDK is now open source Using OpenXML to load an Excel Worksheet into a DataTable (or just how different OpenXML is from the old Excel API we're used too) Using OpenXML SDK to generate Word documents via templates (and without Word being installed) Checking for Microsoft Word DocX/DocM Revisions/Track Changes without using Word... (via OpenXML SDK, LINQ to XML or XML DOM) LINQ to XlsX... Using VB.Net, LINQ, the OpenXML SDK and a little C# helper, to query an Excel XlsX Using native OpenXML to create an XlsX (Which provides an example of why I highlight tools that make OpenXML easier...) Generating Xlsx's on the Server? You're using OpenXML, right? With help from the PowerTools for OpenXML? Official boat-load, as in supertanker, sized OpenXML content list (Insert "One OpenXML content list to rule them all" here) So how do I get from here to OpenXML? Got a map for you, an Open XML SDK Blog Map… Where to go to scratch your OpenXML dev info itch… "Open XML Explained" Free eBook (PDF) The Noob's Guide to Open XML Dev (If you know how to spell OpenXML but that's about it, this is your Getting Started guide...) Reusing the PowerShell PowerTools for Open XML in your C# or VB.Net world PowerShell, OpenXML, WMI and the PowerTools for OpenXML = Doc generation for our inner geek Because it’s a PowerShell kind of day… PowerTools for Open XML V1.1 Released OpenXML PowerTools updated – Cell your Excel via PowerShell Powering into OpenXML with PowerShell Open XML SDK 2.0 for Microsoft Office Released – Automate Office documents without Office Open XML 2.0 Code Snippets for VS2010 (and VS2008 too) Open XML Format SDK 2.0 Code Snippets for Visual Studio 2008 – 52 C#/VB Code Snippets to help ease your Open XML coding Open XML File Format Code Snippets for Visual Studio 2005 (Office 2007 NOT required) Open XML SDK v1 Released OpenXML Viewer 1.0 Released – Open source DocX to HTML conversion, with IE, Firefox and Opera (and/or command line) support

For JMX you need an interface: package com.bos.jmx; public interface ShutdownMBean { /** * Shutdown operation */ public void shutdown() throws Exception; } The implementation is Shutdown java class above. Include this code on server startup used in my Main.java: public void initServerJMX() throws MalformedObjectNameException, InstanceAlreadyExistsException, MBeanRegistrationException, NotCompliantMBeanException { // Initialise JMX // Get the Platform MBean Server MBeanServer mbs = ManagementFactory.getPlatformMBeanServer(); // Construct the ObjectName for the Shutdown MBean we will register ObjectName mbeanName = new ObjectName("com.bos.jmx:type=Shutdown"); // Create the Shutdown MBean final Shutdown mbean = new Shutdown(); // Register the Hello World MBean mbs.registerMBean(mbean, mbeanName); Runtime.getRuntime().addShutdownHook(new Thread() { public void run() { try { mbean.shutdown(); } catch (Exception e) { e.printStackTrace(); } } }); } public void useArg0(String arg) { //sample code using arg } Include this code in client used to shutdown the server used in my Main.java: public void clientExecuteShutdown(int port) throws Exception { JMXServiceURL url = new JMXServiceURL("service:jmx:rmi:///jndi/rmi://:" + port + "/jmxrmi"); JMXConnector jmxc = JMXConnectorFactory.connect(url, null); MBeanServerConnection mbsc = jmxc.getMBeanServerConnection(); // Construct the ObjectName for the Shutdown MBean // ObjectName mbeanName = new ObjectName("com.bos.jmx:type=Shutdown"); // Create a dedicated proxy for the MBean instead of // going directly through the MBean server connection // ShutdownMBean mbeanProxy = JMX.newMBeanProxy(mbsc, mbeanName, ShutdownMBean.class, true); logger.info("Executing shutdown..."); mbeanProxy.shutdown(); logger.info("Shutdown done."); } My sample start/shutdown code with main used in my Main.java: public static void main(String args[]) throws NumberFormatException, Exception { if (args.length < 1) { throw new RuntimeException( "1. Please specify 1st argument." + "\n2. Please specify 1st argument as shutdown and 2nd argument as port of JMX."); } if ("shutdown".equalsIgnoreCase(args[0])) { if (args.length < 2) { throw new RuntimeException( "Please specify 1st argument as shutdown and 2nd argument as port of JMX."); } clientExecuteShutdown(Integer.valueOf(args[1])); } else { useArg0(args[0]); initServerJMX(); } } This code attached also has Runtime.getRuntime().addShutdownHook() The code startup line is for server: java -Dcom.sun.management.jmxremote.port=9999 -Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.ssl=false -classpath . com.bos.jmx.Main arg0 The code for shutdown of server is: java -classpath . com.bos.jmx.Main shutdown 9999 package com.bos.jmx; public class Shutdown implements ShutdownMBean { private static volatile boolean flagRunOne = false; @Override public void shutdown() throws Exception { if (!flagRunOne) { System.out.println("Server shutting down..."); //Sample shutdown code here Main.shutdown(); System.out.println("Server shutdown."); flagRunOne = true; } } }