That has been my challenge since yesterday. And I think I have just got it :D
Let’s see if I can reconstruct a step-by-step manual:
1. First of all, let have some understanding of the structure of a EAR file.
EAR stands for Enterprise ARchive. It’s a convenient mean to to pack and deploy components of an enterprise application. Essentially, you can pack WAR, EJB, Resource Adapter and supporting libraries inside a EAR file. Having them all in one place, as a single unit tremendously helps release management and deployment. But it does pose some challenges in the context of class-loading.
For weblogic application, each EAR file must contain a application.xml file under META-INF. jwsc will automatically generate this file is none is specified in its applicationXml attribute. However, the generated file only contain 1 entry - the WAR file. In order to use EJB, we will need to overwrite that file by our own. The below ant script will do the work:
<copy overwrite="true" todir="${env.MATRIX_CODEBASE}/${project}/build/ear/META-INF">
<FileSet dir="${env.MATRIX_CODEBASE}/${project}/etc">
<include name="application.xml" />
</FileSet>
</copy>
2. Class-loading. Where you can place library/code shared by both WAR file and EJB.
Web application load classes from either their WEB-INF/classes or WEB-INF/lib directories. EJB as JAR file can depends on dependency mapping in its MANIFEST file.
But be careful when we pack them together. Weblogic class-loaders are organized into hierarchy with Webapp class-loader below EJB’s. Class-loading hell, as I saw the term somewhere, is used to refered to situation when a single class is loaded by both webapp and EJB class-loaders. Everything seems correct, webapp and EJB work fine on their own, but the application breaks down the minute those 2 exchanges objects of type loaded by both class-loaders.
Take some minutes (or even hours) to read weblogic class-loading mechanism. Webapp is under EJB thus is able to delegate the loading task to EJB. The reverse is not possible, EJB cannot load library under webapp’s WEB-INF/lib directory. So, it’s safer to let EJB do class-loading.
3. Build order.
Webapp is the front-end, it’s the one first invoked by client’s request. It will subsequently delegate the task to EJB. So, in order to compile webapp, we will need EJB.
4. Project Structure
EJB requires its own descriptors like ejb-jar.xml and weblogic-ejb-jar.xml. Enterprise Application that uses EJB also requires EJB declaration insides its application.xml. I have them all under /etc folder.
Shared classes and library between EJB and webapp, as explained earlier, can be loaded by EJB class-loader. Hence, they should be stored in a same level with EJB JAR and WAR files. I group them all into -common.jar which is referenced by EJB JAR.
Ok, everything prepared. Let’s get real!
5. Ant script
Step 1: build -common.jar that includes all shared java classes and configuration
Step 2: build -ejb.jar that reference `-common.jar and shared libraries
Step 3: Process JWS file with classpath includes -common.jar, -ejb.jar and shared libraries. The result is a WAR file.
Step 4: Pack all generated file into an EAR file.