How do I access return value of a Java method returning java.lang.String from C++ in JNI?

Question

I am trying to pass back a string from a Java method called from C++. I am not able to find out what JNI function should I call to access the method and be returned a jstrin

Answer 1

You should have

cls = env->FindClass("ClassifierWrapper"); 

Then you need to invoke the constructor to get a new object:

jmethodID classifierConstructor = env->GetMethodID(cls,"", "()V"); 
if (classifierConstructor == NULL) {
  return NULL; /* exception thrown */
}

jobject classifierObj = env->NewObject( cls, classifierConstructor);

You are getting static method (even though the method name is wrong). But you need to get the instance method since getString() is not static.

jmethodID getStringMethod = env->GetMethodID(cls, "getString", "()Ljava/lang/String;"); 

Now invoke the method:

rv = env->CallObjectMethod(classifierObj, getStringMethod, 0); 
const char *strReturn = env->GetStringUTFChars(env, rv, 0);