jne-example.java

@C({
        //includes

        "#include <stlib.h>",

        //global variables
        "static JavaVM*     jvm;",
        "static jclass      handler_class;",
        "static jmethodID   j_func_handle;",

        //defines

        "#define GET_ATTACHED_JENV(jenv){\\",
        "   int getEnvStat = (*jvm)->GetEnv(jvm, (void **)&jenv,JNI_VERSION_1_6);\\",
        "   if (getEnvStat == JNI_EDETACHED) {\\",
        "       (*jvm)->AttachCurrentThread(jvm, (void **) &jenv,NULL);\\",
        "   }\\",
        "}",

        //custom functions

        "JNIEXPORT",
        "jint JNI_OnLoad(JavaVM *vm, void *reserved) {",
        "    jvm = vm;",
        "    return JNI_VERSION_1_6;",
        "}",

        "void handle_callback(void *user_data) {",
        "   JNIEnv * const env;",
        "   GET_ATTACHED_JENV(env);",
        "   jobject handler = (jobject) user_data;",
        "   (*env)->CallVoidMethod(env, handler, j_func_handle);",
        "}"
})
public class Example {

    static{
        registerHandler(Handler.class);
    }

    public static interface Handler {
        void handle();
    }

    @C({
            "handler_class = (*env)->NewGlobalRef(env, clazz);",
            "j_func_handle = (*env)->GetMethodID(env, itf_class, \"handle\", \"()V\");"
    })
    private static native void registerHandler(Class<? extends Handler> clazz);

    //native function body
    @C({
            "const char* first_arg = (*env)->GetStringUTFChars(env, firstArg, 0);",
            "int second_arg = (int) secondArg;",
            "handle_callback(handler)",
            "return (jlong) 1235L;"
    })
    public native long someNativeCall(String firstArg, int secondArg, Handler handler);
}