Java classes and libraries can be used to add sophisticated functionality to a module. There are no specific caveats or constraints on classes and libraries—as long as they do not overtly conflict with existing code (for example, importing a different version of an existing library, such as Xerces), any code can be included in a module.

OpenCms does not offer any tools for developing the Java code inside the CMS. Unlike JSP files, Java code must be written and compiled outside OpenCms, and then the resulting .class or .jar files must be imported. Any time this executable content is added or modified, you must unlock and publish the files so that the code will be copied from the VFS to the real file system, where the Java classloader can find it. Then, you will need to restart the servlet container so that the classes will be loaded.

Our module will contain the code necessary for applying an XSLT stylesheet to an XML document, transforming it into an HTML document...