Issue 1848 - Clean up local reference handling

jni/JniUpdateAvailableCallback.cpp

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2015 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 23 matching lines @@
 JniUpdateAvailableCallback::JniUpdateAvailableCallback(
   JNIEnv* env, jobject callbackObject)
   : JniCallbackBase(env, callbackObject)
 {
 }
 
 void JniUpdateAvailableCallback::Callback(const std::string& arg)
 {
   JNIEnvAcquire env(GetJavaVM());
 
-  jclass clazz = env->GetObjectClass(GetCallbackObject());
-  jmethodID method = env->GetMethodID(clazz, "updateAvailableCallback",
-                                      "(Ljava/lang/String;)V");
+  jmethodID method = env->GetMethodID(
+      *JniLocalReference<jclass>(*env,
+          env->GetObjectClass(GetCallbackObject())), "updateAvailableCallback",
+      "(Ljava/lang/String;)V");
 
   if (method)
   {
-    jstring jArg = env->NewStringUTF(arg.c_str());
-    env->CallVoidMethod(GetCallbackObject(), method, jArg);
+    JniLocalReference<jstring> jArg(*env, env->NewStringUTF(arg.c_str()));
+    env->CallVoidMethod(GetCallbackObject(), method, *jArg);
   }
 
   CheckAndLogJavaException(*env);
 }
 
 static JNINativeMethod methods[] =
 {
   { (char*)"ctor", (char*)"(Ljava/lang/Object;)J", (void*)JniCtor },
   { (char*)"dtor", (char*)"(J)V", (void*)JniDtor }
 };
 
 extern "C" JNIEXPORT void JNICALL
 Java_org_adblockplus_libadblockplus_UpdateAvailableCallback_registerNatives(
   JNIEnv *env, jclass clazz)
 {
   env->RegisterNatives(clazz, methods, sizeof(methods) / sizeof(methods[0]));
 }