The Java Interface is designed for ease-of-use. A WSDL is generated for you and the JARs and other resources are automatically deployed in a BPR file. However, you must keep the Java project simple by following the requirements outlined in Constraints for your Java Project.

If your BPEL process requires custom Java code that handles asynchronous call-backs, policy assertions, and other details, you can use the Java wrapper custom invoke handler, as described in EJB/Java Invoke Handler Properties Dialog.