Alex Theedom

It's best practice to centralize the management of properties than hard code values at the location of use. This allows for the reuse of values and better maintenance.

In a DataWeave script, you can reference an application property defined in a properties files by using the p function of the dw::Mule module.

The mapObject DataWeave function transform data contained in an object. It iterates over each key/value pair, applies a transformation to each key, and outputs an object.

The DataWeave map function is used to transform data contained in an array. It does this by iterating over the elements in the array and applying a transformation to each element.

The pluck function is used to retrieve the key, value, and index from an object and output the result to an array.

In Java there are various ways to negate a predicate in the Stream API's filter method. In this post I present four approaches.

Java EE 8 brings with it a lot of goodness, so let's take a look at the top five of these new features!

Getting HTTPS up and running for your Java EE app is as simple as adding some XML. Let's look at configuring your app for more secure communication.

When using JAX-RS resource methods, be sure you know how to maintain your Lists' generic types. This guide will tell you how to handle type erasure.

Want to see what the new JSON Pointer, straight from the JSON-P 1.1 API, is capable of? Here's a challenge and a corresponding explanation.

Here is everything you need to know about the ongoing design, philosophy, and process of developing the MicroProfile initiative.

Let's talk about accessing HTTP objects using JSP, the newer and preferred JSF, and how to use Expression Language in your Java EE projects.

Java EE 8 saw updates to JSON processing. Check out what's new with the JSON-P API, the two models it offers for JSON processing, and their basic methods.

This collection of hints, tips, and tricks will ensure your Strings are formatted just how you want them. Keep it bookmarked for when you need it.

With Java Enums, there are two similar, but different methods that are commonly used: name() and toString(). Learn the difference and when to use both for best results.

Continuing with our journey of the @Context annotation, let's see how you can inject Servlet request and response classes into your Java EE projects.

This three-part series on JAX-RS annotations starts off with some of the simpler rules and annotations and their roles in the Java EE world.

When using JAX-RS, we often need to make use of the @Context annotation. But what exactly does it do? And what separates it from @Inject.

Take a look at how Java EE began, how it's grown and adapted to microservices and the cloud, and an overview of what's coming in Java EE 8.

Familiarize yourself with resource injection using the JAX-RS API. We'll cover the annotations methods you can use to pass needed information.

The singleton pattern is one of the most well-known design patterns... wait, or is it an anti-pattern? See how to implement the singleton in Java EE, and look at some of the pros and cons.

HTTP/2 removes bottlenecks from client/server communication. With the specification now official, vendor support is become more mature.

Spring 4 is widely used, but as with any technology, there are loads of questions. Here are the most asked and answered questions on Stackoverflow, like differences in component and controller annotations, and what the Spring framework is actually used for.

Learn more about installing a cluster on a single machine and how to add more nodes to your cluster.

In this article I will go through a common set-up for a small production environment. A single tier, load balanced application server cluster. Overview A high level overview of what we will be doing. Downloading and installing Apache HTTP server and mod_jk Downloading Tomcat Downloading Java Configuring two local Tomcat servers Clustering the two Tomcat servers Configuring Apache to use mod_jk to forward request to Tomcat Deploying application to Tomcat server that tests our set-up Introduction What is Apache? Apache is an HTTP server. What is mod_jk? It is an Apache module that allows AJP communication between Apache and a back end application server like Tomcat.I am running this on Ubuntu 14.04LTS installed on a dual boot PC with Windows 7. Download Apache2 We are going to use Ubuntu's APT package maintenance system to obtain and install Apache2. sudo apt-get install apache2 This will install in /etc/apache2 Download and install mod_jk The mod_jk module is not included in the Apache2 download so must be obtained and installed separately. The installation requires that the mod_jk module is visible to Apache and configured to ensure that Apache knows where to look for it and what to do with the requests you want to proxy. sudo apt-get install libapache2-mod-jk This will install in /etc/libapache2-mod-jk also two files have been added to the /etc/apache2/mods-available folder. Downloading and installing Tomcat 8 At the time of writing this Tomcat 8 does not have a package in APT so you must download the binaries from the tomcat website.http://tomcat.apache.org/download-80.cgi select the appropriate binary distribution and extract it as follows. tar xvzf apache-tomcat-8.0.5.tar.gz We need two copies of the Tomcat server to be load balanced. I created two directories in the /opt/ location: /opt/tomcat-server1/ and /opt/tomcat-server2/ and copied tomcat into each one. Download and install Java Download Java from APT as follows: apt-get install openjdk-7-jdk and set JAVA_HOME in .bashrc vim ~/.bashrc export JAVA_HOME=/usr/lib/jvm/java-7-openjdk-amd64 Configure two local Tomcat servers We will edit only the server.xml of the server2 installation of tomcat. We need to change port numbers to avoid conflicts.We change the following: and comment out the HTTP Connector as we only want the web application to be accessible through the load balancer.Here is my server2 Tomcat server.xml configuration. Configure mod_jk Load balancing is configured in the workers.properties file, located /etc/libapache2-mod-jk/ where workers represent actual or virtual workers.We will define two actual workers and two virtual workers which map to the Tomcat servers. In the worker.list property I have defined two virtual workers: status and loadbalancer, I will refer to these later in the Apache configuration.Workers for each server have been defined using values for the server.xml configuration files. I used the port values for the AJP connectors and I have included an lbfactor that sets the preference that the load balancer will show for that server.Finally we define the virtual workers. The loadbalancer worker is set to type lb and set the workers that represent the Tomcat servers in the balancer_workers properties. The status only needs to be set to type status. worker.list=loadbalancer,status worker.server1.port=8009worker.server1.host=localhostworker.server1.type=ajp13 worker.server2.port=9009worker.server2.host=localhostworker.server2.type=ajp13 worker.server1.lbfactor=1worker.server2.lbfactor=1 worker.loadbalancer.type=lbworker.loadbalancer.balance_workers=server1,server2 worker.status.type=status Ensure that you remove any other worker configuration that are not being used. Configure Apache Web Server to forward requests You will need to add the following to the Apache configurations located in etc/apache2/sites-enabled/000-default.conf JkMount /status status JkMount /* loadbalancer Verify the installation To test that all has been configured correctly we need to deploy an application. A sample application that has been used for years to test such configurations is called the ClusterJSP sample application. You can find it by googling in or from the JBoss site.Now deploy the war to the webapps folder on both servers and start each server using the start-up script /opt/tomcat-server1/bin/startup.sh.Go to http://localhost/clusterjsp/HaJsp.jsp and you should see the page show HttpSession information. Now lets look at the mod_jk status page: http://localhost/status. You will see that this page shows information about the load balancer workers and the workers it is balancing. If everything is working you will see the worker error state show OK or OK/IDLE if they are not currently balancing load. Things to try out Enable sticky sessions: Configure jvmRoute in the server.xml configuration. Further reading Loadbalancing with mod_jk and ApacheWorking with mod_jk Connecting Apache's Web Server to Multiple Instances of Tomcat

What is the Strategy Design Pattern? The Strategy design pattern is designed to provide a way of selecting from a range of interchangeable strategies. How is it implemented? Classic implementation requires that each Strategy implements an interface and provides a concrete implementation for an execute method. The strategy is selected and the execute method called via an interface reference. Classic implementation of the Strategy Design Pattern The strategy interface that must be implemented by all strategies. public interface Strategy { public void execute(); } Two classes showing the implementation of the Strategy interface and a concrete implementation of the execute method. public class StrategyA implements Strategy { @Override public void execute(){ System.out.print("Executing strategy A"); } } public class StrategyB implements Strategy { @Override public void execute() { System.out.print("Executing strategy B"); } } The context class selects the strategy and executes the execute method of the selected strategy. public class Context { private Strategy strategy; public void setStrategy(Strategy strategy){ this.strategy = strategy; } public void executeStrategy(){ this.strategy.execute(); } } An example of using the Strategy. public class UseStrategy { public static void main(String[] args){ Context context = new Context(); context.setStrategy(new StrategyA()); context.executeStrategy(); context.setStrategy(new StrategyB()); context.executeStrategy(); } } Enum implementation of the Strategy Design Pattern Now lets look at the above example implemented as an enum. This implementation only requires two classes: an enum class and a class that uses it. All the magic happens in the enum where the concrete implementation of the strategy is done in the definition of each enum constant. public enum Strategy { STRATEGY_A { @Override void execute(){ System.out.print("Executing strategy A"); } }, STRATEGY_B { @Override void execute(){ System.out.print("Executing strategy B"); } }; abstract void execute(); } We use this implementation as follows: public class UseStrategy { public static void main(String[] args){ UseStrategy useStrategy = new UseStrategy(); useStrategy.perform(Strategy.STRATEGY_A); useStrategy.perform(Strategy.STRATEGY_B); } private void perform(Strategy strategy){ strategy.execute(); } } EnumMap implementation of the Strategy design pattern Alternatively the enum can be selected from a map of Strategies where the key is the enum itself. This is shown in the following example using an EnumMap. public class EnumMapExample { static EnumMap lookupStrategy= new EnumMap<>(Strategy.class); { lookupStrategy.put(Strategy.STRATEGY_A, Strategy.STRATEGY_A); lookupStrategy.put(Strategy.STRATEGY_B, Strategy.STRATEGY_B); } public static void main(String[] args){ lookupStrategy.get(Strategy.valueOf("STRATEGY_A")).execute(); lookupStrategy.get(Strategy.valueOf("STRATEGY_B")).execute(); } } Open In Codenvy To save time you can view this code directly in your browser by using codenvy's cloud IDE. Click this link to view this code now. Links Git hub repository of this code source Codenvy IDE pre-installed with all the code from this article