Question

1. Can I enumerate all native methods in java, those that have to be
   implemented in c/c++ using JNI?
2. Can I enumerate native methods by
   name (there could be multiple overloads with the same name)?
3. How can I retrieve method signature to be able to generate the method
   signature used by JNI?

Is there a way to check if all native jni methods have been bound properly, instead of trying to call them and get java.lang.UnsatisfiedLinkError exceptions. Sometimes method signature changes on either side without properly updating java or c++ side and I’d like to add some debugging code to detect these issues and handle them (perhaps by generating proper method signature and printing it to the log so I can easily fix the code).

I prefer JNI solution, but if something can be done with help on java side then it’s ok also.
If I use registerNatives and register methods that weren’t declared in java then it fails and prints it to logcat:

E/dalvikvm( 1445): ERROR: couldn't find native method
E/dalvikvm( 1445): Requested: Lcom/bla/bla/bla/Test;.nativeTestXX:()Z

but I’d like to catch this error and handle it myself. Is it possible to do it?

EDIT:
In my JNI code I have a static nativeInit (as suggested in Android JNI tips) that registers all native methods. In that same function I’d like to verify that all native methods are properly bound. That is, I don’t need to wait till some uninitialized method is called and the app exists. The problem that I have: there is a lot of jni code written at different times by different ppl and some methods simply became incorrect, but they are used only in some obscure conditions. The best way for me, I think, is to check that all native methods are bound to some c++ function. The other problem, is that part of JNI code uses binding by exporting all these Long_java_names where method signature changes on either side cannot be detected.

Answer 1

There is no call to check for “unbound” native methods. Using RegisterNatives to perform explicit registration ensures that all methods you register have a matching declaration in the Java sources, but there is no way to check for native-declared methods for which there is no implementation (other than calling it and catching the exception).

At the point where a method with a native implementation is called, if nothing has yet been registered then Dalvik will search through the various shared libraries to find a match. What it sounds like you want is a way to force this search and check the result without actually calling the method. There is no such thing.

There are various ways to generate lists of native-declared methods, either statically or at runtime, but you also need a way to determine if an implementation is available. You’re better off in the long run having unit tests that exercise the code.