What is the JDK feature? Does this mean my account supports JSP or Tomcat?

The JDK feature mentioned on many of our hosting plans refers to the Sun Java Development Kit, which is a development tool that will allow you to compile Java applets and applications on the server, but this is not the same as servlet technologies such as Tomcat or JSP. The applets/applications that your create and compile with JDK still depend on client-side Java support.