How to call java method from jni side?

Question

I have done some c-code functions in jni side, and all workings fine.

public native String getMessage() 

function is returning string from jni

Answer 1

My suggestion :

Create a class which will receive the string (you can also use an interface or an abstract class) :

class ResultHandler { 
    public void onReturnedString(String str) 
    { 
        /* Do something with the string */ 
    } 
}

Then change the prototype of your function :

public native void getMessagewithoutReturn(ResultHandler handler);

and the native function will become :

void  Java_com_foo_bar_getMessagewithoutReturn(JNIEnv *env, jobject thiz, jobject handler);

Now you have to call the onReturnedString of the handler so you have to use JNI functions:

 jmethodID mid;
 jclass handlerClass = (*env)->FindClass(env, "com/foo/bar/ResultHandler");
 if (handlerClass == NULL) {
     /* error handling */
 }
 mid = (*env)->GetMethodID(env, handlerClass, "onReturnedString", "(Ljava/lang/String;)V");
 if (mid == NULL) {
     /* error handling */
 }

Then when you need to call the function : (I suppose that resultString is a jstring)

 (*env)->CallVoidMethod(env, handler, mid, resultString);

I have not tested the code but you have the basic ideas.

Some references and sample code here