As I mentioned in another post about a month ago I’ve been playing around with a neo4j graph in which I have the following relationship between nodes: One thing I wanted to do was work out which node is the most connected on the graph, which would tell me who’s worked with the most people. I started off with the following cypher query: query = " START n = node(*)" query << " MATCH n-[r:colleagues]->c" query << " WHERE n.type? = 'person' and has(n.name)" query << " RETURN n.name, count(r) AS connections" query << " ORDER BY connections DESC" I can then execute that via the neo4j console or through irb using the neography gem like so: > require 'rubygems' > require 'neography' > neo = Neography::Rest.new(:port => 7476) > neo.execute_query query # cut for brevity {"data"=>[["Carlos Villela", 283], ["Mark Needham", 221]], "columns"=>["n.name", "connections"]} That shows me each person and the number of people they’ve worked with but I wanted to be able to see the most connected person in each office . Each person is assigned to an office while they’re working out of that office but people tend to move around so they’ll have links to multiple offices: I put ‘start_date’ and ‘end_date’ properties on the ‘member_of’ relationship and we can work out a person’s current office by finding the ‘member_of’ relationship which doesn’t have an end date defined: query = " START n = node(*)" query << " MATCH n-[r:colleagues]->c, n-[r2:member_of]->office" query << " WHERE n.type? = 'person' and has(n.name) and not(has(r2.end_date))" query << " RETURN n.name, count(r) AS connections, office.name" query << " ORDER BY connections DESC" And now our results look more like this: {"data"=>[["Carlos Villela", 283, "Porto Alegre - Brazil"], ["Mark Needham", 221, "London - UK South"]], "columns"=>["n.name", "connections"]} If we want to restrict that just to return the people for a specific person we can do that as well: query = " START n = node(*)" query << " MATCH n-[r:colleagues]->c, n-[r2:member_of]->office" query << " WHERE n.type? = 'person' and has(n.name) and (not(has(r2.end_date))) and office.name = 'London - UK South'" query << " RETURN n.name, count(r) AS connections, office.name" query << " ORDER BY connections DESC" {"data"=>[["Mark Needham", 221, "London - UK South"]], "columns"=>["n.name", "connections"]} In the current version of cypher we need to put brackets around the not expression otherwise it will apply the not to the rest of the where clause. Another way to get around that would be to put the not part of the where clause at the end of the line. While I am able to work out the most connected person by using these queries I’m not sure that it actually tells you who the most connected person is because it’s heavily biased towards people who have worked on big teams. Some ways to try and account for this are to bias the connectivity in favour of those you have worked longer with and also to give less weight to big teams since you’re less likely to have a strong connection with everyone as you might in a smaller team. I haven’t got onto that yet though!

Manipulating JAXWS header on the client Side like adding WSS username token or logging saop message.

I think like everyone, I go through the same journey whenever I find out about a new technology.. Huh? –> This is really cool –> I use it everywhere –> Hmm, sometimes it’s not so great Remember when people were writing websites with XSLT transforms? Yes, exactly. XML is great for storing a data structure as a string, but you really don’t want to be coding your application’s business logic with it. I’ve gone through a similar journey with Object Relational Mapping tools. After hand-coding my DALs, then code generating them, ORMs seemed like the answer to all my problems. I became an enthusiastic user of NHibernate through a number of large enterprise application builds. Even today I would still use an ORM for most classes of enterprise application. However there are some scenarios where ORMs are best avoided. Let me introduce my easy to use, ‘when to use an ORM’ chart. It’s got two axis, ‘Model Complexity’ and ‘Throughput’. The X-axis, Model Complexity, describes the complexity of your domain model; how many entities you have and how complex their relationships are. ORMs excel at mapping complex models between your domain and your database. If you have this kind of model, using an ORM can significantly speed up and simplify your development time and you’d be a fool not to use one. The problem with ORMs is that they are a leaky abstraction. You can’t really use them and not understand how they are communicating with your relational model. The mapping can be complex and you have to have a good grasp of both your relational database, how it responds to SQL requests, and how your ORM comes to generate both the relational schema and the SQL that talks to it. Thinking of ORMs as a way to avoid getting to grips with SQL, tables, and indexes will only lead to pain and suffering. Their benefit is that they automate the grunt work and save you the boring task of writing all that tedious CRUD column to property mapping code. The Y-axis in the chart, Throughput, describes the transactional throughput of your system. At very high levels, hundreds of transactions per second, you need hard-core DBA foo to get out of the deadlocked hell where you will inevitably find yourself. When you need this kind of scalability you can’t treat your ORM as anything other than a very leaky abstraction. You will have to tweak both the schema and the SQL it generates. At very high levels you’ll need Ayende level NHibernate skills to avoid grinding to a halt. If you have a simple model, but very high throughput, experience tells me that an ORM is more trouble than it’s worth. You’ll end up spending so much time fine tuning your relational model and your SQL that it simply acts as an unwanted obfuscation layer. In fact, at the top end of scalability you should question the choice of a relational ACID model entirely and consider an eventually-consistent event based architecture. Similarly, if your model is simple and you don’t have high throughput, you might be better off using a simple data mapper like SimpleData. So, to sum up, ORMs are great, but think twice before using one where you have a simple model and high throughput.

In Spring 3.1 there is a nice new feature: "@Valid On @RequestBody Controller Method Arguments" From the documentation: "An @RequestBody method argument can be annotated with @Valid to invoke automatic validation similar to the support for @ModelAttribute method arguments. A resulting MethodArgumentNotValidException is handled in the DefaultHandlerExceptionResolver and results in a 400 response code." http://static.springsource.org/spring/docs/current/spring-framework-reference/html/new-in-3.1.html#d0e1654 Based on this new feature I am able to send objects in JSON format, validate them and check for possible errors. Before this feature was introduced my controller looked like this: @Controller @RequestMapping("/user") public class UserController { @RequestMapping(method=RequestMethod.POST) public ResponseEntity create(@Valid User user, BindingResult bindingResult) { if (bindingResult.hasErrors()) { //parse errors and send back to user } ... } But data wasn't sent as a JSON object. It came from simple HTML form. Let's play with Spring 3.1. I've updated my maven depedency to use version 3.1.1.RELEASE and added the Jackson dependency to be able to use the MappingJacksonHttpMessageConverter. cglib cglib-nodep 2.2 org.springframework spring-webmvc 3.1.1.RELEASE org.hibernate hibernate-validator 4.3.0.Final org.codehaus.jackson jackson-mapper-asl 1.9.7 All other configuration is placed in java class instead of xml: @Configuration @EnableWebMvc public class WebappConfig { @Bean public UserController userController() { return new UserController(); } @Bean public MappingJacksonJsonView mappingJacksonJsonView() { return new MappingJacksonJsonView(); } @Bean public ContentNegotiatingViewResolver contentNegotiatingViewResolver() { final ContentNegotiatingViewResolver contentNegotiatingViewResolver = new ContentNegotiatingViewResolver(); contentNegotiatingViewResolver.setDefaultContentType(MediaType.APPLICATION_JSON); final ArrayList defaultViews = new ArrayList(); defaultViews.add(mappingJacksonJsonView()); contentNegotiatingViewResolver.setDefaultViews(defaultViews); return contentNegotiatingViewResolver; } } After that I've changed my create method to: @RequestMapping(method=RequestMethod.POST, consumes = "application/json") public ResponseEntity create(@Valid @RequestBody User user, BindingResult bindingResult) { if (bindingResult.hasErrors()) { //parse errors and send back to user } ... Now I've sent a JSON object but received the following error: "An Errors/BindingResult argument is expected to be immediately after the model attribute argument in the controller method signature" According to the documentation "BindingResult is supported only after @ModelAttribute arguments" After removing BindingResult from my method's arguments it worked. But how to get the errors now ? According to the documentation a MethodArgumentNotValidException will be thrown. So let's declare the necessary ExceptionHandler. @ExceptionHandler(MethodArgumentNotValidException.class) public ResponseEntity handleMethodArgumentNotValidException( MethodArgumentNotValidException error ) { return parseErrors(error.getBindingResult()); } ... And that's all, I'm attaching the full source code as a working example.

While preparing my next exercise I had to first find a way how to connect to a remote SLSB from Spring. It turned out to be childishly simple. See how I did it. Writing SLSB component First I needed a remote SLSB. Using M2Eclipse create a Maven 2 project. From the archetypes selection window I typed mojo in filter field (mojo archetypes are codehaus archetypes, I wrote about them in: Don't use org.apache.maven.archetypes!) and selected ejb3 archetype. I wrote a simple SLSB component: package org.xh.studies.openejb; import javax.ejb.Remote; @Remote public interface Greeter { String sayHello(String to); } package org.xh.studies.openejb; import javax.ejb.Stateless; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; @Stateless public class GreeterImpl implements Greeter { private static final Log log = LogFactory.getLog(GreeterImpl.class); public String sayHello(String to) { log.info("Saying hi to: " + to); return "Hello " + to + "! How are you?"; } } I built it with: mvn package Deploying to OpenEJB I downloaded OpenEJB archive from here: http://openejb.apache.org/download.html and unzipped it. I was done with installation :) I copied built in previous step jar to apps directory, then went to bin directory and ran openejb(.bat). Writing JUnit integration test First I wrote a simple integration test (using failsafe plugin, there are many post on my blog about it, the key one is: Maven2 integration testing with failsafe and jetty plugins) to verify if the SLSB is actually working: public class GreeterIT { private static Context ctx; @BeforeClass public static void setUp() throws NamingException { Properties env = new Properties(); env.put(Context.INITIAL_CONTEXT_FACTORY, "org.apache.openejb.client.RemoteInitialContextFactory"); env.put(Context.PROVIDER_URL, "ejbd://localhost:4201"); ctx = new InitialContext(env); } @AfterClass public static void tearDown() throws NamingException { ctx.close(); } @Test public void sayHelloRemoteEJBTest() throws NamingException { Greeter greeter = (Greeter) ctx.lookup("GreeterImplRemote"); String result = greeter.sayHello("Łukasz"); String expected = "Hello Łukasz! How are you?"; Assert.assertEquals(expected, result); } } I ran the test and it passed. Connecting to EJB from Spring I found out a Spring component called org.springframework.ejb.access.SimpleRemoteStatelessSessionProxyFactoryBean. It uses AOP behinde the scenes to create a proxy for a remote SLSB. All you need is just an interface. First I had to add Spring dependencies to my pom.xml. These were: spring-beans spring-context spring-aop Then I created a file called META-INF/spring/beans.xml and wrote: org.apache.openejb.client.RemoteInitialContextFactory ejbd://localhost:4201 In the above file I created a greeterBean which was a dynamic proxy and, thanks to AOP, would behave like a Greeter object. Writing Spring test I added one more field to my test: private static ApplicationContext springCtx; Then in @BeforeClass class I added ApplicationContext initialisation code: springCtx = new ClassPathXmlApplicationContext("META-INF/spring/beans.xml"); Finally I wrote a new method to test what I intended to do first, connecting to a remote SLSB from Spring: @Test public void sayHelloSpringProxyTest() throws NamingException { Greeter greeter = (Greeter) springCtx.getBean("greeterBean"); String result = greeter.sayHello("Łukasz"); String expected = "Hello Łukasz! How are you?"; Assert.assertEquals(expected, result); } It worked! Source code download A complete source code download can be found here: Connecting-to-EJB-from-Spring.zip. Summary Isn't it beautiful? You get an instance of a remote SLSB as a Spring bean. I definitely like it! thanks, Łukasz

Short blog post today. These are a couple of generic serialize and deserialize methods that can be easily used when needing to serialize and deserialize classes. The methods work with any .Net type. That includes built-in .Net types and custom classes that you might create yourself. These methods will only serialize PUBLIC properties of a class. Also, the XML will be human-readable instead of one long line of text. Serialize Method /// /// Serializes the data in the object to the designated file path /// /// Type of Object to serialize /// Object to serialize /// FilePath for the XML file public static void Serialize(T dataToSerialize, string filePath) { try { using (Stream stream = File.Open(filePath, FileMode.Create, FileAccess.ReadWrite)) { XmlSerializer serializer = new XmlSerializer(typeof(T)); XmlTextWriter writer = new XmlTextWriter(stream, Encoding.Default); writer.Formatting = Formatting.Indented; serializer.Serialize(writer, dataToSerialize); writer.Close(); } } catch { throw; } } Deserialize Method /// /// Deserializes the data in the XML file into an object /// /// Type of object to deserialize /// FilePath to XML file /// Object containing deserialized data public static T Deserialize(string filePath) { try { XmlSerializer serializer = new XmlSerializer(typeof(T)); T serializedData; using (Stream stream = File.Open(filePath, FileMode.Open, FileAccess.Read)) { serializedData = (T)serializer.Deserialize(stream); } return serializedData; } catch { throw; } } Here is some sample code to show the methods in action. Person p = new Person() { Name = "John Doe", Age = 42 }; XmlHelper.Serialize(p, @"D:\text.xml"); Person p2 = new Person(); p2 = XmlHelper.Deserialize(@"D:\text.xml"); Console.WriteLine("Name: {0}", p2.Name); Console.WriteLine("Age: {0}", p2.Age); Console.Read();

If you are using Spring to access/configure resources (DAOs/services), then you might as well add some basic performance monitoring while you are at it. This is a trivial task with Spring AOP and doesn't require any changes to existing code, just some simple configuration. First, you need to include the spring-aop, aspectj and cglib libraries. If you are using Maven, simply include the following dependencies... org.aspectj aspectjweaver 1.5.4 cglib cglib-nodep 2.2 org.springframework spring-aop 2.5.6 Next, identify what needs monitoring and put the AOP hooks in place. Generally, this just requires adding a pointcut and advisor configuration in your existing Spring XML configuration file. This configuration will add method response time logging to all methods in the "com.mycompany.services" package. Note: these classes must be instantiated with the Spring context...otherwise, the AOP hooks will not be executed. Next, you need to setup your logging (log4j, etc) to enable TRACE on the interceptor class. That's it, now when you run your application, you will see the following logging... TRACE PerformanceMonitorInterceptor - StopWatch 'PerfTestService.processRequest': running time (millis) = 1322 TRACE PerformanceMonitorInterceptor - StopWatch 'PerfTestService.processRequest': running time (millis) = 98 TRACE PerformanceMonitorInterceptor - StopWatch 'PerfTestService.processRequest': running time (millis) = 1764 This is a some great raw data, but unfortunately is not very useful on its own. Its for every method call and doesn't provide any other stats. This quickly clutters up the log and without some way to process/aggregate the log entries, its hard to make sense out of it. So, unless you plan of writing some log parsing or using 3rd party software (like Splunk or Cati), then you really should do some processing of the data before writing it to the log file. One easy way to do this is to just write a simple interceptor class to use instead of the Spring default one (PerformanceMonitorInterceptor). Below is an example of this that provides periodic stats (last, average and greatest response time) as well as warning whenever a method response time exceeds a configured threshold. By default, it will log stats every 10 method calls and log a warning message anytime a method response time exceeds 1000ms. public class PerfInterceptor implements MethodInterceptor { Logger logger = LoggerFactory.getLogger(PerfInterceptor.class.getName()); private static ConcurrentHashMap methodStats = new ConcurrentHashMap(); private static long statLogFrequency = 10; private static long methodWarningThreshold = 1000; public Object invoke(MethodInvocation method) throws Throwable { long start = System.currentTimeMillis(); try { return method.proceed(); } finally { updateStats(method.getMethod().getName(),(System.currentTimeMillis() - start)); } } private void updateStats(String methodName, long elapsedTime) { MethodStats stats = methodStats.get(methodName); if(stats == null) { stats = new MethodStats(methodName); methodStats.put(methodName,stats); } stats.count++; stats.totalTime += elapsedTime; if(elapsedTime > stats.maxTime) { stats.maxTime = elapsedTime; } if(elapsedTime > methodWarningThreshold) { logger.warn("method warning: " + methodName + "(), cnt = " + stats.count + ", lastTime = " + elapsedTime + ", maxTime = " + stats.maxTime); } if(stats.count % statLogFrequency == 0) { long avgTime = stats.totalTime / stats.count; long runningAvg = (stats.totalTime-stats.lastTotalTime) / statLogFrequency; logger.debug("method: " + methodName + "(), cnt = " + stats.count + ", lastTime = " + elapsedTime + ", avgTime = " + avgTime + ", runningAvg = " + runningAvg + ", maxTime = " + stats.maxTime); //reset the last total time stats.lastTotalTime = stats.totalTime; } } class MethodStats { public String methodName; public long count; public long totalTime; public long lastTotalTime; public long maxTime; public MethodStats(String methodName) { this.methodName = methodName; } } } Now, you just need to wire this into your app by referencing this class in your Spring xml and logging config. When you run your app, you will see stats like this... WARN PerfInterceptor - method warning: processRequest(), cnt = 10, lastTime = 1072, maxTime = 1937 TRACE PerfInterceptor - method: processRequest(), cnt = 10, lastTime = 1072, avgTime = 1243, runningAvg = 1243, maxTime = 1937 WARN PerfInterceptor - method warning: processRequest(), cnt = 20, lastTime = 1466, maxTime = 1937 TRACE PerfInterceptor - method: processRequest(), cnt = 20, lastTime = 1466, avgTime = 1067, runningAvg = 892, maxTime = 1937 As you can see, these stats can provide valuable feedback about class/method performance with very little effort and without modifying any existing Java code. This information can easily be used to find bottlenecks in your application (generally database or threading related, etc)...good luck

Introduction: Building modern HTTP/RESTful/RPC services has become very easy with the new ASP.NET Web API framework. Using ASP.NET Web API framework, you can create HTTP services which can be accessed from browsers, machines, mobile devices and other clients. Developing HTTP services is now quite easy for ASP.NET MVC developer becasue ASP.NET Web API is now included in ASP.NET MVC. In addition to developing HTTP services, it is also important to return meaningful response to client if a resource(uri) not found(HTTP 404) for a reason(for example, mistyped resource uri). It is also important to make this response centralized so you can configure all of 'HTTP 404 Not Found' resource at one place. In this article, I will show you how to handle 'HTTP 404 Not Found' at one place. Description: Let's say that you are developing a HTTP RESTful application using ASP.NET Web API framework. In this application you need to handle HTTP 404 errors in a centralized location. From ASP.NET Web API point of you, you need to handle these situations, No route matched. Route is matched but no {controller} has been found on route. No type with {controller} name has been found. No matching action method found in the selected controller due to no action method start with the request HTTP method verb or no action method with IActionHttpMethodProviderRoute implemented attribute found or no method with {action} name found or no method with the matching {action} name found. Now, let create a ErrorController with Handle404 action method. This action method will be used in all of the above cases for sending HTTP 404 response message to the client. public class ErrorController : ApiController { [HttpGet, HttpPost, HttpPut, HttpDelete, HttpHead, HttpOptions, AcceptVerbs("PATCH")] public HttpResponseMessage Handle404() { var responseMessage = new HttpResponseMessage(HttpStatusCode.NotFound); responseMessage.ReasonPhrase = "The requested resource is not found"; return responseMessage; } } You can easily change the above action method to send some other specific HTTP 404 error response. If a client of your HTTP service send a request to a resource(uri) and no route matched with this uri on server then you can route the request to the above Handle404 method using a custom route. Put this route at the very bottom of route configuration, routes.MapHttpRoute( name: "Error404", routeTemplate: "{*url}", defaults: new { controller = "Error", action = "Handle404" } ); Now you need handle the case when there is no {controller} in the matching route or when there is no type with {controller} name found. You can easily handle this case and route the request to the above Handle404 method using a custom IHttpControllerSelector. Here is the definition of a custom IHttpControllerSelector, public class HttpNotFoundAwareDefaultHttpControllerSelector : DefaultHttpControllerSelector { public HttpNotFoundAwareDefaultHttpControllerSelector(HttpConfiguration configuration) : base(configuration) { } public override HttpControllerDescriptor SelectController(HttpRequestMessage request) { HttpControllerDescriptor decriptor = null; try { decriptor = base.SelectController(request); } catch (HttpResponseException ex) { var code = ex.Response.StatusCode; if (code != HttpStatusCode.NotFound) throw; var routeValues = request.GetRouteData().Values; routeValues["controller"] = "Error"; routeValues["action"] = "Handle404"; decriptor = base.SelectController(request); } return decriptor; } } Next, it is also required to pass the request to the above Handle404 method if no matching action method found in the selected controller due to the reason discussed above. This situation can also be easily handled through a custom IHttpActionSelector. Here is the source of custom IHttpActionSelector, public class HttpNotFoundAwareControllerActionSelector : ApiControllerActionSelector { public HttpNotFoundAwareControllerActionSelector() { } public override HttpActionDescriptor SelectAction(HttpControllerContext controllerContext) { HttpActionDescriptor decriptor = null; try { decriptor = base.SelectAction(controllerContext); } catch (HttpResponseException ex) { var code = ex.Response.StatusCode; if (code != HttpStatusCode.NotFound && code != HttpStatusCode.MethodNotAllowed) throw; var routeData = controllerContext.RouteData; routeData.Values["action"] = "Handle404"; IHttpController httpController = new ErrorController(); controllerContext.Controller = httpController; controllerContext.ControllerDescriptor = new HttpControllerDescriptor(controllerContext.Configuration, "Error", httpController.GetType()); decriptor = base.SelectAction(controllerContext); } return decriptor; } } Finally, we need to register the custom IHttpControllerSelector and IHttpActionSelector. Open global.asax.cs file and add these lines, configuration.Services.Replace(typeof(IHttpControllerSelector), new HttpNotFoundAwareDefaultHttpControllerSelector(configuration)); configuration.Services.Replace(typeof(IHttpActionSelector), new HttpNotFoundAwareControllerActionSelector()); Summary: In addition to building an application for HTTP services, it is also important to send meaningful centralized information in response when something goes wrong, for example 'HTTP 404 Not Found' error. In this article, I showed you how to handle 'HTTP 404 Not Found' error in a centralized location. Hopefully you will enjoy this article too.

Here is a quick example of how to programmatically access ActiveMQ MBeans to monitor and manipulate message queues... First, get a connection to a JMX server (assumes localhost, port 1099, no auth) Note, always cache the connection for subsequent requests (can cause memory utilization issues otherwise) JMXServiceURL url = new JMXServiceURL("service:jmx:rmi:///jndi/rmi://localhost:1099/jmxrmi"); JMXConnector jmxc = JMXConnectorFactory.connect(url); MBeanServerConnection conn = jmxc.getMBeanServerConnection(); Then, you can execute various operations such as addQueue, removeQueue, etc... String operationName="addQueue"; String parameter="MyNewQueue"; ObjectName activeMQ = new ObjectName("org.apache.activemq:BrokerName=localhost,Type=Broker"); if(parameter != null) { Object[] params = {parameter}; String[] sig = {"java.lang.String"}; conn.invoke(activeMQ, operationName, params, sig); } else { conn.invoke(activeMQ, operationName,null,null); } Also, you can get an ActiveMQ QueueViewMBean instance for a specified queue name... ObjectName activeMQ = new ObjectName("org.apache.activemq:BrokerName=localhost,Type=Broker"); BrokerViewMBean mbean = (BrokerViewMBean) MBeanServerInvocationHandler.newProxyInstance(conn, activeMQ,BrokerViewMBean.class, true); for (ObjectName name : mbean.getQueues()) { QueueViewMBean queueMbean = (QueueViewMBean) MBeanServerInvocationHandler.newProxyInstance(mbsc, name, QueueViewMBean.class, true); if (queueMbean.getName().equals(queueName)) { queueViewBeanCache.put(cacheKey, queueMbean); return queueMbean; } } Then, execute one of several APIs against the QueueViewMBean instance... Queue monitoring - getEnqueueCount(), getDequeueCount(), getConsumerCount(), etc... Queue manipulation - purge(), getMessage(String messageId), removeMessage(String messageId), moveMessageTo(String messageId, String destinationName), copyMessageTo(String messageId, String destinationName), etc... Summary The APIs can easily be used to build a web or command line based tool to support remote ActiveMQ management features. That being said, all of these features are available via the JMX console itself and ActiveMQ does provide a web console to support some management/monitoring tasks. See these pages for more information... http://activemq.apache.org/jmx-support.html http://activemq.apache.org/web-console.html

Spring 3.1 now includes support for the long awaited environment aware feature called profiles. Now we can activate profiles in our application, which allows us to define beans by deployment regions, such as “dev”, “qa”, “production”, “cloud”, etc. We also can use this feature for other purposes: defining profiles for performance testing scenarios such as “cached” or “lazyload”. Essential Tokens Spring profiles are enabled using the case insensitive tokens spring.profiles.active or spring_profiles_active. This token can be set as: an Environment Variable a JVM Property Web Parameter Programmatic Spring also looks for the token, spring.profiles.default, which can be used to set the default profile(s) if none are specified with spring.profiles.active. Grouping Beans by Profile Spring 3.1 provides nested bean definitions, providing the ability to define beans for various environments: Nested must appear last in the file. Beans that are used in all profiles are declared in the outer as we always have, such as Service classes. If we put a single declaration at below any nested tags we will get the exception org.xml.sax.SAXParseException: cvc-complex-type.2.4.a: Invalid content was found starting with element 'bean'. Multiple beans can now share the same XML “id” In a typical scenario, we would want the DataSource bean to be called dataSource in both all profiles. Spring now allow us to create multiple beans within an XML file with the same ID providing they are defined in different sets. In other words, ID uniqueness is only enforced within each set. Automatic Profile Discovery (Programmatic) We can configure a class to set our profile(s) during application startup by implementing the appropriate interface. For example, we may configure an application to set different profiles based on where the application is deployed – in CloudFoundry or running as a local web application. In the web.xml file we can include an Servlet context parameter, contextInitializerClasses, to bootstrap this class: contextInitializerClasses com.gordondickens.springthreeone.services.CloudApplicationContextInitializer The Initializer class package com.gordondickens.springthreeone.services; import org.cloudfoundry.runtime.env.CloudEnvironment; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.springframework.context.ApplicationContextInitializer; import org.springframework.context.ConfigurableApplicationContext; public class CloudApplicationContextInitializer implements ApplicationContextInitializer { private static final Logger logger = LoggerFactory .getLogger(CloudApplicationContextInitializer.class); @Override public void initialize(ConfigurableApplicationContext applicationContext) { CloudEnvironment env = new CloudEnvironment(); if (env.getInstanceInfo() != null) { logger.info("Application running in cloud. API '{}'", env.getCloudApiUri()); applicationContext.getEnvironment().setActiveProfiles("cloud"); applicationContext.refresh(); } else { logger.info("Application running local"); applicationContext.getEnvironment().setActiveProfiles("dev"); } } } Annotation Support for JavaConfig If we are are using JavaConfig to define our beans, Spring 3.1 includes the @Profile annotation for enabling bean config files by profile(s). package com.gordondickens.springthreeone.configuration; import com.gordondickens.springthreeone.SimpleBean; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.Profile; @Configuration @Profile("dev") public class AppConfig { @Bean public SimpleBean simpleBean() { SimpleBean simpleBean = new SimpleBean(); simpleBean.setMyString("Ripped Pants"); return simpleBean; } } Testing with XML Configuration With XML configuration we can simply add the annotation @ActiveProfiles to the JUnit test class. To include multiple profiles, use the format @ActiveProfiles(profiles = {"dev", "prod"}) package com.gordondickens.springthreeone; import org.junit.Test; import org.junit.runner.RunWith; import org.springframework.beans.factory.NoSuchBeanDefinitionException; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.context.ApplicationContext; import org.springframework.test.context.ActiveProfiles; import org.springframework.test.context.ContextConfiguration; import org.springframework.test.context.junit4.SpringJUnit4ClassRunner; import static junit.framework.Assert.assertNotNull; import static junit.framework.Assert.assertNull; @RunWith(SpringJUnit4ClassRunner.class) @ContextConfiguration @ActiveProfiles(profiles = "dev") public class DevBeansTest { @Autowired ApplicationContext applicationContext; @Test public void testDevBeans() { SimpleBean simpleBean = applicationContext.getBean("constructorBean", SimpleBean.class); assertNotNull(simpleBean); } @Test(expected = NoSuchBeanDefinitionException.class) public void testProdBean() { SimpleBean prodBean = applicationContext.getBean("prodBean", SimpleBean.class); assertNull(prodBean); } } Testing with JavaConfig JavaConfig allows us to configure Spring with or without XML configuration. If we want to test beans that are defined in a Configuration class we configure our test with the loader and classes arguments of the @ContextConfiguration annotation. package com.gordondickens.springthreeone.configuration; import com.gordondickens.springthreeone.SimpleBean; import org.junit.Test; import org.junit.runner.RunWith; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.test.context.ActiveProfiles; import org.springframework.test.context.ContextConfiguration; import org.springframework.test.context.junit4.SpringJUnit4ClassRunner; import org.springframework.test.context.support.AnnotationConfigContextLoader; import static org.junit.Assert.assertNotNull; @RunWith(SpringJUnit4ClassRunner.class) @ContextConfiguration(classes = AppConfig.class, loader = AnnotationConfigContextLoader.class) @ActiveProfiles(profiles = "dev") public class BeanConfigTest { @Autowired SimpleBean simpleBean; @Test public void testBeanAvailablity() { assertNotNull(simpleBean); } } Declarative Configuration in WEB.XML If we desire to set the configuration in WEB.XML, this can be done with parameters on ContextLoaderListener. Application Context contextConfigLocation /WEB-INF/app-config.xml spring.profiles.active DOUBLEUPMINT Log Results DEBUG PropertySourcesPropertyResolver - Found key 'spring.profiles.active' in [servletContextInitParams] with type [String] and value 'DOUBLEUPMINT' Environment Variable/JVM Parameter Setting an environment variable can be done with either spring_profiles_default or spring_profiles_active. In Unix/Mac it would be export SPRING_PROFILES_DEFAULT=DEVELOPMENT for my local system. We can also use the JVM “-D” parameter which also works with Maven when using Tomcat or Jetty plugins. Note: Remember the tokens are NOT case sensitive and can use periods or underscores as separators. For Unix systems, you need to use the underscore, as above. Logging of system level properties DEBUG PropertySourcesPropertyResolver - Found key 'spring.profiles.default' in [systemProperties] with type [String] and value 'dev,default' Summary Now we are equipped to activate various Spring bean sets, based on profiles we define. We can use traditional, XML based configuration, or the features added to support JavaConfig originally introduced in Spring 3.0.

Check out an example of the volatile Java keyword.

CSS3 Fade slider Today I would like to show you how to create nice and smooth css3 slider. It uses fade effect to switch between slides. Plus, you can use custom promo text for each slide. We will use basic UL-LI unordered list to make this slider. We don’t need to click anywhere to switch slides – everything is automatically (css3 animation). Live Demo download result So, lets start Step 1. HTML Html markup is very easy. There are four slides. Each slide consists of image (as background) and promo text in DIV. If you need – you always can add more slides here. Promo text #1 Promo text #2 Promo text #3 Promo text #4 Step 2. CSS Now, it’s time to define css styles for our slider. Here are styles for main slider element, inner slides and for promo titles: /* fade slider */ .slides { height:300px; margin:50px auto; overflow:hidden; position:relative; width:900px; } .slides ul { list-style:none; position:relative; } /* keyframes #anim_slides */ @-webkit-keyframes anim_slides { 0% { opacity:0; } 6% { opacity:1; } 24% { opacity:1; } 30% { opacity:0; } 100% { opacity:0; } } @-moz-keyframes anim_slides { 0% { opacity:0; } 6% { opacity:1; } 24% { opacity:1; } 30% { opacity:0; } 100% { opacity:0; } } .slides ul li { opacity:0; position:absolute; top:0; /* css3 animation */ -webkit-animation-name: anim_slides; -webkit-animation-duration: 24.0s; -webkit-animation-timing-function: linear; -webkit-animation-iteration-count: infinite; -webkit-animation-direction: normal; -webkit-animation-delay: 0; -webkit-animation-play-state: running; -webkit-animation-fill-mode: forwards; -moz-animation-name: anim_slides; -moz-animation-duration: 24.0s; -moz-animation-timing-function: linear; -moz-animation-iteration-count: infinite; -moz-animation-direction: normal; -moz-animation-delay: 0; -moz-animation-play-state: running; -moz-animation-fill-mode: forwards; } /* css3 delays */ .slides ul li:nth-child(2), .slides ul li:nth-child(2) div { -webkit-animation-delay: 6.0s; -moz-animation-delay: 6.0s; } .slides ul li:nth-child(3), .slides ul li:nth-child(3) div { -webkit-animation-delay: 12.0s; -moz-animation-delay: 12.0s; } .slides ul li:nth-child(4), .slides ul li:nth-child(4) div { -webkit-animation-delay: 18.0s; -moz-animation-delay: 18.0s; } .slides ul li img { display:block; } /* keyframes #anim_titles */ @-webkit-keyframes anim_titles { 0% { left:100%; opacity:0; } 5% { left:10%; opacity:1; } 20% { left:10%; opacity:1; } 25% { left:100%; opacity:0; } 100% { left:100%; opacity:0; } } @-moz-keyframes anim_titles { 0% { left:100%; opacity:0; } 5% { left:10%; opacity:1; } 20% { left:10%; opacity:1; } 25% { left:100%; opacity:0; } 100% { left:100%; opacity:0; } } .slides ul li div { background-color:#000000; border-radius:10px 10px 10px 10px; box-shadow:0 0 5px #FFFFFF inset; color:#FFFFFF; font-size:26px; left:10%; margin:0 auto; padding:20px; position:absolute; top:50%; width:200px; /* css3 animation */ -webkit-animation-name: anim_titles; -webkit-animation-duration: 24.0s; -webkit-animation-timing-function: linear; -webkit-animation-iteration-count: infinite; -webkit-animation-direction: normal; -webkit-animation-delay: 0; -webkit-animation-play-state: running; -webkit-animation-fill-mode: forwards; -moz-animation-name: anim_titles; -moz-animation-duration: 24.0s; -moz-animation-timing-function: linear; -moz-animation-iteration-count: infinite; -moz-animation-direction: normal; -moz-animation-delay: 0; -moz-animation-play-state: running; -moz-animation-fill-mode: forwards; } You can see that I use two css3 animations here: anim_slides and anim_titles. First one is for separated slides, second one – for promo texts. In order to switch between slides – we change opacity of slides. For titles – we change Left position and opacity too. Live Demo download result Conclusion That is all for today. We have just created new cool pure CSS3-based slider with Fade effect. I hope that you like it. Good luck!

from timeit import default_timer class Timer(object): def __init__(self, verbose=False): self.verbose = verbose self.timer = default_timer def __enter__(self): self.start = self.timer() return self def __exit__(self, *args): end = self.timer() self.elapsed_secs = end - self.start self.elapsed = self.elapsed_secs * 1000 # millisecs if self.verbose: print 'elapsed time: %f ms' % self.elapsed To use the Timer (context manager object), invoke it using Python's `with` statement. The duration of the context (code inside your `with` block) will be timed. It uses the appropriate timer for your platform, via the `timeit` module. Timer is used like this: with Timer() as target: # block of code goes here. # result (elapsed time) is stored in `target` properties. Example script: timing a web request (HTTP GET), using the `requests` module. #!/usr/bin/env python import requests from timer import Timer url = 'https://github.com/timeline.json' with Timer() as t: r = requests.get(url) print 'fetched %r in %.2f millisecs' % (url, t.elapsed) Output: fetched 'https://github.com/timeline.json' in 458.76 millisecs `timer.py` in GitHub Gist form, with more examples: #!/usr/bin/env python # # Python Timer Class - Context Manager for Timing Code Blocks # Corey Goldberg - 2012 # from timeit import default_timer class Timer(object): def __init__(self, verbose=False): self.verbose = verbose self.timer = default_timer def __enter__(self): self.start = self.timer() return self def __exit__(self, *args): end = self.timer() self.elapsed_secs = end - self.start self.elapsed = self.elapsed_secs * 1000 # millisecs if self.verbose: print 'elapsed time: %f ms' % self.elapsed if __name__ == '__main__': # example: # 'HTTP GET' from requests module, inside timer blocks. # invoke the Timer context manager using the `with` statement. import requests url = 'https://github.com/timeline.json' # verbose (auto) timer output with Timer(verbose=True): r = requests.get(url) # print stored elapsed time in milliseconds with Timer() as t: r = requests.get(url) print 'response time (millisecs): %.2f' % t.elapsed # print stored elapsed time in seconds with Timer() as t: r = requests.get(url) print 'response time (secs): %.3f' % t.elapsed_secs # example output: # # $ python timer.py # elapsed time: 652.403831 ms # response time (millisecs): 635.49 # response time (secs): 0.624

Performance problems are one of the biggest challenges to expect when designing and implementing Java EE related technologies.

There are several cool ways to create PDFs with Python. In this article we will be focusing on a cool little tool called rst2pdf, which takes a text file that contains Restructured Text and converts it to a PDF. The rst2pdf package requires Reportlab to function. This won’t be a tutorial on Restructured Text, although we’ll have to discuss it to some degree just to understand what’s going on. Getting Started First off we’ll need to create a document with the required markup. Let’s do that first. Here’s some simple restructured text with a couple of directives mixed in. We’ll explain everything after you’ve had a chance to read the code: .. header:: Python Rules! - page ###Page### ===== Title ===== This is some blah blah blah .. raw:: pdf PageBreak oneColumn New section =========== yada yada yada import urllib import urllib2 import webbrowser url = "http://duckduckgo.com/html" data = urllib.urlencode({'q': 'Python'}) results = urllib2.urlopen(url, data) with open("results.html", "w") as f: f.write(results.read()) webbrowser.open("results.html") The first couple lines define the header that will be on every page. In this case, we’re going to have “Python Rules!” printed at the top of every page along with a page number. There are several other special hash-mark insert directives available. You should check out the official documentation for more information on those. Then we have a Title. Note that it is preceded and followed by a bunch of equal signs that are the same length as the text. This tells us that this text will be styled and centered. The following line is just a lame sentence for demonstration purposes. Next up is another special directive which tells rst2pdf to insert a page break. The second page contains a section header, a lame sentence and a code example that’s color-coded. To generate the PDF, you’ll need to do something like this on the command line: rst2pdf test.rst -o out.pdf You can also run rst2pdf against a config file to control some of the special PDF directives, like header and footer, etc. The information about how to make the config file get read is a little confusing though. It sounds like you have to place the file in a specific location: /etc/rst2pdf.conf and ~/.rst2pdf/config. There’s also a –config flag you can pass, but I’ve found various reports online that that doesn’t work, so your mileage may vary. There’s a sample config file in the project’s repo that you’ll find instructive. Wrapping Up I was hoping that rst2pdf would allow an easy way to specify absolute positions and create lines and boxes so I could replace an XSL / XML project I was working on with something much more simple. Alas, rst2pdf just doesn’t support the lines and boxes that reportlab itself does at the time of this writing. However if you need something easy to use to create your documents with and you already know restructured text, I think this is a very good way to go. You can also take your restructured text skills and use them with the Sphinx documentation project.

Innodb can indexes built by sort since Innodb Plugin for MySQL 5.1 which is a lot faster than building them through insertion, especially for tables much larger than memory and large uncorrelated indexes you might be looking at 10x difference or more. Yet for some reason Innodb team has chosen to use very small (just 1MB) and hard coded buffer for this operation, which means almost any such index build operation has to use excessive sort merge passes significantly slowing down index built process. Mark Callaghan and Facebook Team has fixed this in their tree back in early 2011 adding innodb_merge_sort_block_size variable and I was thinking this small patch will be merged to MySQL 5.5 promptly, yet it has not happen to date. Here is example of gains you can expect (courtesy of Alexey Kopytov), using 1Mil rows Sysbench table. Buffer Length | alter table sbtest add key(c) 1MB 34 sec 8MB 26 sec 100MB 21 sec 128MB 17 sec REBUILD 37 sec REBUILD in this table is using “fast_index_creation=0″ which allows to disable fast index creation in Percona Server and force complete table to be rebuilt instead. Looking at this data we can see even for such small table there is possible to improve index creation time 2x by using large buffer. Also we can see we can substantially improve performance even increasing it from 1MB to 8MB, which might be sensible as default as even small systems should be able to allocate 8MB to do alter table. You may be wondering why in this case table rebuild is so close in performance to building index by sort with small buffer – this comes from building index on long character field with very short length, Innodb would use fixed size records for sort space which results in a lot more work done than you would otherwise need. Having some optimization to better deal with this case also would be nice. The table also was fitting in buffer pool completely in this case which means table rebuild could have done fast too. Results are from Percona Server 5.5.24

Usually we have some required fields on our forms and it would be nice if ASP.NET MVC views can detect those fields automatically and display nice red asterisk after field label. As this functionality is not built in I built my own solution based on data annotations. In this posting I will show you how to show red asterisk after label of required fields. Here are the main information sources I used when working out my own solution: How can I modify LabelFor to display an asterisk on required fields? (stackoverflow) ASP.NET MVC – Display visual hints for the required fields in your model (Radu Enucă) Although my code was first written for completely different situation I needed it later and I modified it to work with models that use data annotations. If data member of model has Required attribute set then asterisk is rendered after field. If Required attribute is missing then there will be no asterisk. Here’s my code. You can take just LabelForRequired() methods and paste them to your own HTML extension class. public static class HtmlExtensions { [SuppressMessage("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures", Justification = "This is an appropriate nesting of generic types")] public static MvcHtmlString LabelForRequired(this HtmlHelper html, Expression> expression, string labelText = "") { return LabelHelper(html, ModelMetadata.FromLambdaExpression(expression, html.ViewData), ExpressionHelper.GetExpressionText(expression), labelText); } private static MvcHtmlString LabelHelper(HtmlHelper html, ModelMetadata metadata, string htmlFieldName, string labelText) { if (string.IsNullOrEmpty(labelText)) { labelText = metadata.DisplayName ?? metadata.PropertyName ?? htmlFieldName.Split('.').Last(); } if (string.IsNullOrEmpty(labelText)) { return MvcHtmlString.Empty; } bool isRequired = false; if (metadata.ContainerType != null) { isRequired = metadata.ContainerType.GetProperty(metadata.PropertyName) .GetCustomAttributes(typeof(RequiredAttribute), false) .Length == 1; } TagBuilder tag = new TagBuilder("label"); tag.Attributes.Add( "for", TagBuilder.CreateSanitizedId( html.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(htmlFieldName) ) ); if (isRequired) tag.Attributes.Add("class", "label-required"); tag.SetInnerText(labelText); var output = tag.ToString(TagRenderMode.Normal); if (isRequired) { var asteriskTag = new TagBuilder("span"); asteriskTag.Attributes.Add("class", "required"); asteriskTag.SetInnerText("*"); output += asteriskTag.ToString(TagRenderMode.Normal); } return MvcHtmlString.Create(output); } } And here’s how to use LabelForRequired extension method in your view: @Html.LabelForRequired(m => m.Name) @Html.TextBoxFor(m => m.Name) @Html.ValidationMessageFor(m => m.Name) After playing with CSS style called .required my example form looks like this: These red asterisks are not part of original view mark-up. LabelForRequired method detected that these properties have Required attribute set and rendered out asterisks after field names. NB! By default asterisks are not red. You have to define CSS class called “required” to modify how asterisk looks like and how it is positioned.

Apache Camel has a very powerful bean injection framework which allows developers to focus only on solving business problems. However there are situations when you need to do a little bit more. Read below to see how easy it is to setup aspects (AspectJ) in Apache Camel. Use case In Qualitas I have an installation route which consists of 10 mandatory and 2 optional processors. Some processors like property resolvers or validators don't modify contents of message's body so I have to always copy body from the in message to out message. Also, all my processors require some headers to function properly. Finally, I would like to get a status updated after each of my processors either finishes processing successfully or fails. Setting up AspectJ This is just a plain Spring configuration frankly. All you have to do is: Apache Camel processor aspect To define aspect in AspectJ I used AspectJ-specific @Aspect and @Around annotations: @Aspect @Component @Order(Ordered.LOWEST) public class HeadersAndBodyCopierAspect { @Around("execution(* com.googlecode.qualitas.internal.installation..*.process(org.apache.camel.Exchange)) && args(exchange) && target(org.apache.camel.Processor)") public Object copyHeadersAndBody(ProceedingJoinPoint pjp, Exchange exchange) throws Throwable { Object retValue = pjp.proceed(); Message in = exchange.getIn(); Message out = exchange.getOut(); // always copy headers out.setHeaders(in.getHeaders()); // if output body is empty copy it from input if (out.getBody() == null) { out.setBody(in.getBody()); } return retValue; } } I also used @Order Spring-specific annotation to control the order of execution of my aspects and @Component for automatic context scanning. Now, the join point is defined as execution(* com.googlecode.qualitas.internal.installation..*.process(org.apache.camel.Exchange)) && args(exchange) && target(org.apache.camel.Processor) which basically means: apply this aspect to all process methods which are defined in all classes in com.googlecode.qualitas.internal.installation or subpackages and which take Exchange object as an argument there can be many custom methods whose names may be process and whose argument may be Exchange, so I added one more constraint, this class has to be an instance of Processor args(exchange) allows me to add Exchange object as an argument to my aspect More complex aspects and source code Of course in Spring you can inject other beans directly into your aspects. I used it in my ProcessStatusUpdaterAspect aspect which you can find in Qualitas repo on GoogleCode or GitHub. If you are interested in trying out the whole Qualitas system take a look at the following two links: BuildingTheProject and RunningTheProject. cheers, Łukasz

This article is part 2 of our NoClassDefFoundError troubleshooting series. It will focus and describe the simplest type of NoClassDefFoundError problem. This article is ideal for Java beginners and I highly recommend that you compile and run the sample Java program yourself. The following writing format will be used going forward and will provide you with: - Description of the problem case and type of NoClassDefFoundError - Sample Java program “simulating” the problem case - ClassLoader chain view - Recommendations and resolution strategies NoClassDefFoundError problem case 1 – missing JAR file The first problem case we will cover is related to a Java program packaging and / or classpath problem. A typical Java program can include one or many JAR files created at compile time. NoClassDefFoundError can often be observed when you forget to add JAR file(s) containing Java classes referenced by your Java or Java EE application. This type of problem is normally not hard to resolve once you analyze the Java Exception and missing Java class name. Sample Java program The following simple Java program is split as per below: - The main Java program NoClassDefFoundErrorSimulator - The caller Java class CallerClassA - The referencing Java class ReferencingClassA - A util class for ClassLoader and logging related facilities JavaEETrainingUtil This program is simple attempting to create a new instance and execute a method of the Java class CallerClassA which is referencing the class ReferencingClassA.It will demonstrate how a simple classpath problem can trigger NoClassDefFoundError. The program is also displaying detail on the current class loader chain at class loading time in order to help you keep track of this process. This will be especially useful for future and more complex problem cases when dealing with larger class loader chains. #### NoClassDefFoundErrorSimulator.java package org.ph.javaee.training1; import org.ph.javaee.training.util.JavaEETrainingUtil; /** * NoClassDefFoundErrorTraining1 * @author Pierre-Hugues Charbonneau * */ public class NoClassDefFoundErrorSimulator { /** * @param args */ public static void main(String[] args) { System.out.println("java.lang.NoClassDefFoundError Simulator - Training 1"); System.out.println("Author: Pierre-Hugues Charbonneau"); System.out.println("http://javaeesupportpatterns.blogspot.com"); // Print current Classloader context System.out.println("\nCurrent ClassLoader chain: "+JavaEETrainingUtil.getCurrentClassloaderDetail()); // 1. Create a new instance of CallerClassA CallerClassA caller = new CallerClassA(); // 2. Execute method of the caller caller.doSomething(); System.out.println("done!"); } } #### CallerClassA.java package org.ph.javaee.training1; import org.ph.javaee.training.util.JavaEETrainingUtil; /** * CallerClassA * @author Pierre-Hugues Charbonneau * */ public class CallerClassA { private final static String CLAZZ = CallerClassA.class.getName(); static { System.out.println("Classloading of "+CLAZZ+" in progress..."+JavaEETrainingUtil.getCurrentClassloaderDetail()); } public CallerClassA() { System.out.println("Creating a new instance of "+CallerClassA.class.getName()+"..."); } public void doSomething() { // Create a new instance of ReferencingClassA ReferencingClassA referencingClass = new ReferencingClassA(); } } #### ReferencingClassA.java package org.ph.javaee.training1; import org.ph.javaee.training.util.JavaEETrainingUtil; /** * ReferencingClassA * @author Pierre-Hugues Charbonneau * */ public class ReferencingClassA { private final static String CLAZZ = ReferencingClassA.class.getName(); static { System.out.println("Classloading of "+CLAZZ+" in progress..."+JavaEETrainingUtil.getCurrentClassloaderDetail()); } public ReferencingClassA() { System.out.println("Creating a new instance of "+ReferencingClassA.class.getName()+"..."); } public void doSomething() { //nothing to do... } } #### JavaEETrainingUtil.java package org.ph.javaee.training.util; import java.util.Stack; import java.lang.ClassLoader; /** * JavaEETrainingUtil * @author Pierre-Hugues Charbonneau * */ public class JavaEETrainingUtil { /** * getCurrentClassloaderDetail * @return */ public static String getCurrentClassloaderDetail() { StringBuffer classLoaderDetail = new StringBuffer(); Stack classLoaderStack = new Stack(); ClassLoader currentClassLoader = Thread.currentThread().getContextClassLoader(); classLoaderDetail.append("\n-----------------------------------------------------------------\n"); // Build a Stack of the current ClassLoader chain while (currentClassLoader != null) { classLoaderStack.push(currentClassLoader); currentClassLoader = currentClassLoader.getParent(); } // Print ClassLoader parent chain while(classLoaderStack.size() > 0) { ClassLoader classLoader = classLoaderStack.pop(); // Print current classLoaderDetail.append(classLoader); if (classLoaderStack.size() > 0) { classLoaderDetail.append("\n--- delegation ---\n"); } else { classLoaderDetail.append(" **Current ClassLoader**"); } } classLoaderDetail.append("\n-----------------------------------------------------------------\n"); return classLoaderDetail.toString(); } } Problem reproduction In order to replicate the problem, we will simply “voluntary” omit one of the JAR files from the classpath that contains the referencing Java class ReferencingClassA. The Java program is packaged as per below: - MainProgram.jar (contains NoClassDefFoundErrorSimulator.class and JavaEETrainingUtil.class) - CallerClassA.jar (contains CallerClassA.class) - ReferencingClassA.jar (contains ReferencingClassA.class) Now, let’s run the program as is: ## Baseline (normal execution) .\bin>java -classpath CallerClassA.jar;ReferencingClassA.jar;MainProgram.jar org.ph.javaee.training1.NoClassDefFoundErrorSimulator java.lang.NoClassDefFoundError Simulator - Training 1 Author: Pierre-Hugues Charbonneau http://javaeesupportpatterns.blogspot.com Current ClassLoader chain: ----------------------------------------------------------------- sun.misc.Launcher$ExtClassLoader@17c1e333 --- delegation --- sun.misc.Launcher$AppClassLoader@214c4ac9 **Current ClassLoader** ----------------------------------------------------------------- Classloading of org.ph.javaee.training1.CallerClassA in progress... ----------------------------------------------------------------- sun.misc.Launcher$ExtClassLoader@17c1e333 --- delegation --- sun.misc.Launcher$AppClassLoader@214c4ac9 **Current ClassLoader** ----------------------------------------------------------------- Creating a new instance of org.ph.javaee.training1.CallerClassA... Classloading of org.ph.javaee.training1.ReferencingClassA in progress... ----------------------------------------------------------------- sun.misc.Launcher$ExtClassLoader@17c1e333 --- delegation --- sun.misc.Launcher$AppClassLoader@214c4ac9 **Current ClassLoader** ----------------------------------------------------------------- Creating a new instance of org.ph.javaee.training1.ReferencingClassA... done! For the initial run (baseline), the main program was able to create a new instance of CallerClassA and execute its method successfully; including successful class loading of the referencing class ReferencingClassA. ## Problem reproduction run (with removal of ReferencingClassA.jar) ../bin>java -classpath CallerClassA.jar;MainProgram.jar org.ph.javaee.training1.NoClassDefFoundErrorSimulator java.lang.NoClassDefFoundError Simulator - Training 1 Author: Pierre-Hugues Charbonneau http://javaeesupportpatterns.blogspot.com Current ClassLoader chain: ----------------------------------------------------------------- sun.misc.Launcher$ExtClassLoader@17c1e333 --- delegation --- sun.misc.Launcher$AppClassLoader@214c4ac9 **Current ClassLoader** ----------------------------------------------------------------- Classloading of org.ph.javaee.training1.CallerClassA in progress... ----------------------------------------------------------------- sun.misc.Launcher$ExtClassLoader@17c1e333 --- delegation --- sun.misc.Launcher$AppClassLoader@214c4ac9 **Current ClassLoader** ----------------------------------------------------------------- Creating a new instance of org.ph.javaee.training1.CallerClassA... Exception in thread "main" java.lang.NoClassDefFoundError: org/ph/javaee/training1/ReferencingClassA at org.ph.javaee.training1.CallerClassA.doSomething(CallerClassA.java:25) at org.ph.javaee.training1.NoClassDefFoundErrorSimulator.main(NoClassDefFoundErrorSimulator.java:28) Caused by: java.lang.ClassNotFoundException: org.ph.javaee.training1.ReferencingClassA at java.net.URLClassLoader$1.run(Unknown Source) at java.net.URLClassLoader$1.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) ... 2 more What happened? The removal of the ReferencingClassA.jar, containing ReferencingClassA, did prevent the current class loader to locate this referencing Java class at runtime leading to ClassNotFoundException and NoClassDefFoundError. This is the typical Exception that you will get if you omit JAR file(s) from your Java start-up classpath or within an EAR / WAR for Java EE related applications. ClassLoader view Now let’s review the ClassLoader chain so you can properly understand this problem case. As you saw from the Java program output logging, the following Java ClassLoaders were found: Classloading of org.ph.javaee.training1.CallerClassA in progress... ----------------------------------------------------------------- sun.misc.Launcher$ExtClassLoader@17c1e333 --- delegation --- sun.misc.Launcher$AppClassLoader@214c4ac9 **Current ClassLoader** ----------------------------------------------------------------- ** Please note that the Java bootstrap class loader is responsible to load the core JDK classes and is written in native code ** ## sun.misc.Launcher$AppClassLoader This is the system class loader responsible to load our application code found from the Java classpath specified at start-up. ##sun.misc.Launcher$ExtClassLoader This is the extension class loader responsible to load code in the extensions directories (/lib/ext, or any other directory specified by the java.ext.dirs system property). As you can see from the Java program logging output, the extension class loader is the actual super parent of the system class loader. Our sample Java program was loaded at the system class loader level. Please note that this class loader chain is very simple for this problem case since we did not create child class loaders at this point. This will be covered in future articles. Recommendations and resolution strategies Now find below my recommendations and resolution strategies for NoClassDefFoundError problem case 1: - Review the java.lang.NoClassDefFoundError error and identify the missing Java class - Verify and locate the missing Java class from your compile / build environment - Determine if the missing Java class is from your application code, third part API or even the Java EE container itself. Verify where the missing JAR file(s) is / are expected to be found - Once found, verify your runtime environment Java classpath for any typo or missing JAR file(s) - If the problem is triggered from a Java EE application, perform the same above steps but verify the packaging of your EAR / WAR file for missing JAR and other library file dependencies such as MANIFEST Please feel free to post any question or comment. The part 3 will be available shortly.

There are several code analysis tools for Python. The most well known is pylint. Then there’s pychecker and now we’re moving on to pyflakes. The pyflakes project is a part of something known as the Divmod Project. Pyflakes doesn’t actually execute the code it checks, unlike pychecker. Of course, pylint also doesn’t execute the code. Regardless, we’ll take a quick look at it and see how pyflakes works and if it’s better than the competition. Getting Started As you have probably guessed, pyflakes is not a part of the Python distribution. You will need to download it from PyPI or from the project’s launchpad page. Once you have it installed, you can run it against some of your own code. Or you can follow along and see how it works with our test script. Running pyflakes We’ll be using a super simple and pretty silly example script. In fact, it’s the same one we used for the pylint and pychecker articles. Here it is again for your viewing pleasure: import sys ######################################################################## class CarClass: """""" #---------------------------------------------------------------------- def __init__(self, color, make, model, year): """Constructor""" self.color = color self.make = make self.model = model self.year = year if "Windows" in platform.platform(): print "You're using Windows!" self.weight = self.getWeight(1, 2, 3) #---------------------------------------------------------------------- def getWeight(this): """""" return "2000 lbs" As was noted in the other articles, this dumb code has 4 issues, 3 of which would stop the programming from running. Let’s see what pyflakes can find! Try running the following command and you’ll see the following output: C:\Users\mdriscoll\Desktop>pyflakes crummy_code.py crummy_code.py:1: 'sys' imported but unused crummy_code.py:15: undefined name 'platform' While pyflakes was super fast at returning this output, it didn’t find all the errors. The getWeight method call is passing too many arguments and getWeight method itself is defined incorrectly as it doesn’t have a “self” argument. If you fixed your code according to what pyflakes told you, you’re code still wouldn’t work. Wrapping Up The pyflakes website claims that pyflakes is faster than pychecker and pylint. I didn’t test this, but anyone who wants to can do so pretty easily by just running it against some big files. Maybe grab the BeautifulSoup file or run it (and the others) against something complex like PySide or SQLAlchemy and see how they compare. I personally am disappointed that it didn’t catch all the issues I was looking for. I think for my purposes, I’ll be sticking with pylint. This might be a handy tool for a quick and dirty test or just to make you feel better after a particularly poor result from a pylint scan.