Modern Java application development makes an intensive use of the state-of-the-art frameworks, like Hibernate, Spring, Struts, etc. While JRebel handles Java class re-loading, it is still sometimes necessary to refresh some framework-related code in the application. You might want to add a new bean to your Spring application context, or add a new OR-mapping to your Hibernate configuration. For that, JRebel provides SDK, which can be used to support any framework of your choice. Also, JRebel includes some support for the most popular frameworks. Official plugins are listed at the plugins page and included in the JRebel JAR file (if not stated otherwise). You will need to enable them depending on which framework you are using. JRebel will print out the list of found plugins on application startup and instructions on how to enable those specific plugins.
If you happen to find a JRebel plugin that is not listed at the plugin page and there are no specific instructions on how to install then probably the solution is to drop the plugin in the WEB-INF/lib and check standard output for messages regarding the plugin.
Special treatment of the application environment is done while using Spring Framework, Hibernate, Guice, EJB, JSF, Struts, Tapestry, Seam, AspectJ, Wicket, Toplink, GWT, and many others. There might be some limitations for JRebel to reload the framework-related code depending on what features you use. For the detailed information concerning supported features of the framework of your interest, take a look at the relevant description in the manual.