How can I see the Java source code that a JSP is compiled into

The answer depends on whether you are using Tomcat or Jetty as your web container. 

Tomcat

Tomcat stores the generated source files in the work/jboss.web/HOSTNAME/WEBAPPNAME directory under your ServerConfiguration directory.  

For example, the JSP file somedir/somefile.jsp would generate the Java source file server/default/work/jboss.web/localhost/foo/org/apache/jsp/somedir/somefile_jsp.java.

Jetty

Jetty stores the generated file in the tmp directory  This will normally be the directory specified by the system property java.io.tmpdir.  On UNIX-like systems this will normally be /tmp.