jni call to getClass returns null for a jobject

Question

I am facing issues with making a java call from C++ code using JNI. I am able to get the jobject, but the invoocation of any API on the jobject fails. On digging for nearly one day and comparing with other working Java API (jobjects which i call in my code), i found one difference.

the following piece of code

void printClassInfo(JNIEnv* env, jobject object, jclass klazz)
{
    printf("printclass info 1\n");
    printf("printclass info 2\n");

    // First get the class object
    jmethodID mid = env->GetMethodID(klazz, "getClass", "()Ljava/lang/Class;");
    printf("printclass info 2.1\n");
    jobject clsObj = env->CallObjectMethod(object, mid);
    printf("printclass info 3\n");
    if(clsObj == NULL){
        printf("cls obj is null");
    }
}

prints cls obj is null for the jobject for which I am seeing issues.

For other jobjects, the call does not return null.

The major difference is that it is a newly added class and I seemed to have missed something that can cause this issue. I have rechecked again and again but not getting any clear indicators.

Any help appreciated.

Answer 1

You have the object already. Why do you need its class (sorry klass) at all? JNI has a nic function for you, GetObjectClass(jobject). Here is what you could do:

void printClassInfo(JNIEnv* env, jobject object) {

   jclass clsObj = env->GetObjectClass(env, object);
   if (clsObj == NULL) {
    printf("cls obj is null");
   }
}

Will this solve your problem?