Issue 1848 - Clean up local reference handling

jni/Utils.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 17 matching lines @@
 
   const char* cStr = env->GetStringUTFChars(str, 0);
   std::string ret(cStr);
   env->ReleaseStringUTFChars(str, cStr);
 
   return ret;
 }
 
 jobject NewJniArrayList(JNIEnv* env)
 {
-  jclass clazz = env->FindClass("java/util/ArrayList");
-  jmethodID ctor = env->GetMethodID(clazz, "<init>", "()V");
-  return env->NewObject(clazz, ctor);
+  JniLocalReference<jclass> clazz(env, env->FindClass("java/util/ArrayList"));
+  jmethodID ctor = env->GetMethodID(*clazz, "<init>", "()V");
+  return env->NewObject(*clazz, ctor);
 }
 
 void JniAddObjectToList(JNIEnv* env, jobject list, jobject value)
 {
-  jmethodID add = env->GetMethodID(env->GetObjectClass(list), "add", "(Ljava/lang/Object;)Z");
+  JniLocalReference<jclass> clazz(env, env->GetObjectClass(list));
+  jmethodID add = env->GetMethodID(*clazz, "add", "(Ljava/lang/Object;)Z");
   env->CallBooleanMethod(list, add, value);
 }
 
 void JniThrowException(JNIEnv* env, const std::string& message)
 {
-  jclass clazz = env->FindClass(PKG("AdblockPlusException"));
-  env->ThrowNew(clazz, message.c_str());
+  JniLocalReference<jclass> clazz(env,
+      env->FindClass(PKG("AdblockPlusException")));
+  env->ThrowNew(*clazz, message.c_str());
 }
 
 void JniThrowException(JNIEnv* env, const std::exception& e)
 {
   JniThrowException(env, e.what());
 }
 
 void JniThrowException(JNIEnv* env)
 {
   JniThrowException(env, "Unknown exception from libadblockplus");
@@ skipping 14 matching lines @@
   }
 }
 
 JNIEnvAcquire::~JNIEnvAcquire()
 {
   if (attachmentStatus == JNI_EDETACHED)
   {
     javaVM->DetachCurrentThread();
   }
 }