Issue 1848 - Clean up local reference handling

jni/JniFilterEngine.cpp

Index: jni/JniFilterEngine.cpp
diff --git a/jni/JniFilterEngine.cpp b/jni/JniFilterEngine.cpp
index 7976902711d9e59dd5038bce35cea432d6b40876..07adbb873636eb12dc398eeeaf2a39e99735c118 100644
--- a/jni/JniFilterEngine.cpp
+++ b/jni/JniFilterEngine.cpp
@@ -34,11 +34,11 @@ static jobject SubscriptionsToArrayList(JNIEnv* env, std::vector<AdblockPlus::Su
 static AdblockPlus::FilterEngine::ContentType ConvertContentType(JNIEnv *env,
     jobject jContentType)
 {
-  jclass contentTypeClass = env->GetObjectClass(jContentType);
-  jmethodID nameMethod = env->GetMethodID(contentTypeClass, "name",
+  JniLocalReference<jclass> contentTypeClass(env, env->GetObjectClass(jContentType));
+  jmethodID nameMethod = env->GetMethodID(*contentTypeClass, "name",
                                           "()Ljava/lang/String;");
-  jstring jValue = (jstring) env->CallObjectMethod(jContentType, nameMethod);
-  const std::string value = JniJavaToStdString(env, jValue);
+  JniLocalReference<jstring> jValue(env, (jstring) env->CallObjectMethod(jContentType, nameMethod));
+  const std::string value = JniJavaToStdString(env, *jValue);
   return AdblockPlus::FilterEngine::StringToContentType(value);
 }
 
@@ -94,7 +94,7 @@ static jobject JNICALL JniGetListedFilters(JNIEnv* env, jclass clazz, jlong ptr)
 
     for (std::vector<AdblockPlus::FilterPtr>::iterator it = filters.begin(), end = filters.end(); it != end; it++)
     {
-      JniAddObjectToList(env, list, NewJniFilter(env, *it));
+      JniAddObjectToList(env, list, *JniLocalReference<jobject>(env, NewJniFilter(env, *it)));
     }
 
     return list;
@@ -234,7 +234,7 @@ static jobject JNICALL JniGetElementHidingSelectors(JNIEnv* env, jclass clazz, j
 
     for (std::vector<std::string>::iterator it = selectors.begin(), end = selectors.end(); it != end; it++)
     {
-      JniAddObjectToList(env, list, env->NewStringUTF(it->c_str()));
+      JniAddObjectToList(env, list, *JniLocalReference<jstring>(env, env->NewStringUTF(it->c_str())));
     }
 
     return list;
@@ -274,7 +274,8 @@ static jobject JNICALL JniMatchesMany(JNIEnv* env, jclass clazz, jlong ptr, jstr
 
   for (jsize i = 0; i < len; i++)
   {
-    documentUrls.push_back(JniJavaToStdString(env, static_cast<jstring>(env->GetObjectArrayElement(jDocumentUrls, i))));
+    documentUrls.push_back(JniJavaToStdString(env,
+        *JniLocalReference<jstring>(env, static_cast<jstring>(env->GetObjectArrayElement(jDocumentUrls, i)))));
   }
 
   try