jnixx - making jni smell more like cni

[Andrew Cagney <cagney at redhat dot com>]

Hi,

As part of translating frysk's CNI bindings to JNI, I mocked up a JNI 
bindings generator to simplify the process.  Among its features are:

-- generation of name spaces and a class inheritance structure that 
reflects the java code:
For instance, the lib.dwfl.ElfException class is generated as:
   class lib::dwfl::ElfException : public java::lang::RuntimeException

-- lets you directly invoke methods (wrappers take care of the JNI)
For instance, a static method in LocalMemory can be invoked with:
   java::lang::String s = frysk::testbed::LocalMemory::getModuleName(env)
(yes you still need to pass an env variable round)

-- provides get/set methods for class fields
For instance, given the class variable:
   jint intVar;
a method can read/modify/write it using:
   SetIntVar(env, GetIntVar(env) + 1);

-- lets you use a more natural throw/catch style for handling exceptions
For instance, a try/finally can be implemented using:
   try {
       callJavaMethodFoo();
   catch (java::lang::Throwable e) {
       do cleanup stuff;
       throw e;
   }
(rather than the traditional JNI style of trying to remember to check 
return values for failure)

-- provides wrappers to manage references to array and string elements
For instance, to get at and print a java string as a unix string:
   jstringUTFChars string = jstringUTFChars(env, javaString);
   fprintf(stderr, "string = %s\n", string.elements());

While there are still a few warts and I'd not consider the interfaces 
100% pinned down, the basic framework is working very well.  The curious 
are more than welcome to have a play.  Ideas, suggestions, questions, 
and code are all most welcome.

Andrew