Diabol JAVA

2011-04-07 TOMMY TYNJÄ 

I have lately been looking a bit into the JBoss Shrinkwrap project, which is a simple framework for building archives such as JARs, WARs and EARs with Java code through a straightforward API. You can assemble a simple JAR with a single line of Java code:

JavaArchive jar = ShrinkWrap.create(JavaArchive.class, "myJar.jar")
       .addClasses(MyClass.class, MyOtherClass.class)

With ShrinkWrap you basically have the option to skip the entire build process if you want to. What if you would want to integrate ShrinkWrap with your existing Maven based project? I found myself in a situation where I had a somewhat small web application project setup with Maven, with a single pom.xml which specified war packaging. Due to some external factors I suddenly found myself with a demand of being able to support one of my Spring beans as an EJB. One of the application servers the application should run on demanded that my application was packaged as an ear with the EJB in an own jar with the ejb-jar.xml descriptor file. In this case it would be too much of a trouble to refactor the Spring bean/EJB into an own module with ejb packaging, and then to assemble an ear through the maven-ear-plugin. I also wanted to remain independent of the application server, and wanted to be able to deploy the application as a war artifact on another application server if I wanted to. So I thought I could use ShrinkWrap to help me out.

Add a ShrinkWrap packaging to Maven

I will now describe what I needed to do to add “ShrinkWrap awareness” to my Maven build. I tried to keep this example as simple as possible, therefore I have omitted “unnecessary” configuration, error handling, reusability aspects etc. This example shows you how to build a simple custom EJB jar file with Maven and ShrinkWrap, e.g. together with the build of a war module. First, I obviously had to add the maven dependencies:


I added the api dependency with compile scope as I only need it when building my application. I then added the exec-maven-plugin which basically allows me to execute Java main classes in my Maven build process:


Notice that I specified the package execution phase, which tells Maven to execute the plugin at the package phase of the build process. The plugin will execute the se.diabol.example.MyPackager class with the project build directory as an argument.

Let’s take a look at the se.diabol.example.MyPackager class and the comments on the end of the rows:

public class MyPackager{
   public static void main(final String args[]){
      String buildDir = args[0];          // The build directory, passed as an argument from the exec-maven-plugin
      String jarName = "my_ejb_archive.jar";                   // Chosen jar name
      File actualOutFile = new File(buildDir + "/" + jarName); // The actual output file as a
      JavaArchive ejbJar = ShrinkWrap.create(JavaArchive.class, jarName)
            .addClasses(MyEjbClass.class)                      // Add my EJB class and the ejb-jar.xml
            .addAsResource("ejb-jar.xml");                     // These exist on classpath so ShrinkWrap will find them;    // Create the physical file

Now when you have successfully built your project with e.g. mvn clean package, you will now see that ShrinkWrap created my_ejb_archive.jar archive in the project build directory, containing the MyEjbClass.class and the ejb-jar.xml! When you’ve started off by a simple example like this, you can now move on to more sophisticated solutions and take advantage of ShrinkWraps features.