How to configure rebel.xml

In order to do it’s magic, JavaRebel needs to know where your classes and resources are. We’ll use a rebel.xml configuration file to tell it. This is mandatory when you deploy your app as a WAR/EAR. You’ll need to have one rebel.xml file per module. This includes both web and EJB modules. The rebel.xml configuration file should be placed in your WEB-INF/classes directory in the case of a web module and in the jar root in the case of an ejb module. Put it in the root of a source or resource folder in your project (the same place where the .properties files are).

Configuring JARs

JARs are usually not deployed on their own, but as a part of application (e.g. WEB-INF/lib in WARs or EJB modules in EARs). However often you still want to update their code on-the-fly. Let’s assume that we have a module my-business-module.jar deployed in WEB-INF/lib. You can propagate the changes from your workspace by adding the following rebel.xml to the root of the JAR file:

<?xml version="1.0" encoding="UTF-8"?>
<application
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns="http://www.zeroturnaround.com"
  xsi:schemaLocation="http://www.zeroturnaround.com/alderaan/rebel-2_0.xsd">
  <classpath>
    <dir name="c:\myWorkspace\myBusinessModule\target\classes"/>
    <dir name="c:\myWorkspace\myBusinessModule\src\main\resources"/>
  </classpath>
</application>
    

This will mount classes and resources in directories c:\myWorkspace\myBusinessModule\target\classes and c:\myWorkspace\myBusinessModule\src\main\resources before the classes and resources in the JAR file. Changes to those classes and resources will propagate to the application.

Configuring WARs

In the case of a web application you have web application resources, like JSPs, HTML files, graphic files and so on in addition to the classpath. To configure a web application deployed as a WAR file we create a rebel.xml file in the WEB-INF/classes directory:

<?xml version="1.0" encoding="UTF-8"?>
<application
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns="http://www.zeroturnaround.com"
  xsi:schemaLocation="http://www.zeroturnaround.com/alderaan/rebel-2_0.xsd">
  <classpath>
    <dir name="c:\myWorkspace\myWar\target\classes"/>
    <dir name="c:\myWorkspace\myWar\src\main\resources"/>
  </classpath>
  <web>
    <link target="/">
      <dir name="c:\myWorkspace\myWar\src\main\webapp"/>
    </link>
    <link target="/jsps/">
      <dir name="c:\myWorkspace\myWar\src\main\jsps"/>
    </link>
  </web>
</application>

This will mount classes and resources in directories c:\myWorkspace\myWar\target\classes and c:\myWorkspace\myWar\src\main\resources to the application classpath before the deployed classes and resources. This means that those classes and resources will override the ones in WEB-INF/classes and WEB-INF/lib/*.jar. Changes to those classes and resources will propagate to the application.

This will also map the web resources in the c:\myWorkspace\myWar\src\main\webapp directory to the root (“/”) of the web application context and the web resources in c:\myWorkspace\myWar\src\main\jsps directory under the /jsps/ URI of the web application context. You may map several directories to one context target if necessary.

Configuring EARs

To configure a EAR you need to create a separate rebel.xml file for each EAR module. Web modules should be configured same as individually deployed WARs, EJB modules should be configured same as JARs. If your container supports APP-INF/classes you may also add a rebel.xml to that folder and mount classes and resources that belong to the EAR as a whole.

Tips and Tricks

• Putting absolute paths in the rebel.xml might be a bad idea as you’d like to share it with other team members. Luckily JRebel will expand expressions like “${myProject.root}” in rebel.xml to a system property that you can pass to the application container as -DmyProject.root=c:/myWorkspace/myProject. This allows to use a single configuration for everyone and then customize it when starting the server.
• You are not limited to mounting directories to classpath. You can also mount JARs with <jar>.
• If you need to mount a bunch of directories or JARs at once you can use <dirset> or <jarset> that accepts Ant-style patterns to specify the specific directories.
• You can use Ant FileSet-style include and exclude directives in <dir> and <jar> entries.

Read about those options and more in the configuration manual.