diff --git a/jni/NativeFormats/util/AndroidUtil.cpp b/jni/NativeFormats/util/AndroidUtil.cpp
index e38a0c90b..8651e6792 100644
--- a/jni/NativeFormats/util/AndroidUtil.cpp
+++ b/jni/NativeFormats/util/AndroidUtil.cpp
@@ -25,7 +25,7 @@
 
 JavaVM *AndroidUtil::ourJavaVM = 0;
 
-const char * const AndroidUtil::Class_java_lang_String = "java/lang/String";
+shared_ptr<JavaClass> AndroidUtil::Class_java_lang_String;
 const char * const AndroidUtil::Class_java_util_Collection = "java/util/Collection";
 const char * const AndroidUtil::Class_java_util_Locale = "java/util/Locale";
 const char * const AndroidUtil::Class_java_io_InputStream = "java/io/InputStream";
@@ -124,10 +124,9 @@ bool AndroidUtil::init(JavaVM* jvm) {
 	JNIEnv *env = getEnv();
 	jclass cls;
 
-	CHECK_NULL( cls = env->FindClass(Class_java_lang_String) );
-	Method_java_lang_String_toLowerCase = new StringMethod(env, cls, "toLowerCase", "()");
-	Method_java_lang_String_toUpperCase = new StringMethod(env, cls, "toUpperCase", "()");
-	env->DeleteLocalRef(cls);
+	Class_java_lang_String = new JavaClass(env, "java/lang/String");
+	Method_java_lang_String_toLowerCase = new StringMethod(*Class_java_lang_String, "toLowerCase", "()");
+	Method_java_lang_String_toUpperCase = new StringMethod(*Class_java_lang_String, "toUpperCase", "()");
 
 	CHECK_NULL( cls = env->FindClass(Class_java_util_Collection) );
 	CHECK_NULL( MID_java_util_Collection_toArray = env->GetMethodID(cls, "toArray", "()[Ljava/lang/Object;") );
@@ -313,8 +312,7 @@ jbyteArray AndroidUtil::createJavaByteArray(JNIEnv *env, const std::vector<jbyte
 
 jobjectArray AndroidUtil::createJavaStringArray(JNIEnv *env, const std::vector<std::string> &data) {
 	size_t size = data.size();
-	jclass cls = env->FindClass("java/lang/String");
-	jobjectArray array = env->NewObjectArray(size, cls, 0);
+	jobjectArray array = env->NewObjectArray(size, Class_java_lang_String->j(), 0);
 	for (size_t i = 0; i < size; ++i) {
 		const std::string &str = data[i];
 		if (str.length() > 0) {
@@ -323,7 +321,6 @@ jobjectArray AndroidUtil::createJavaStringArray(JNIEnv *env, const std::vector<s
 			env->DeleteLocalRef(javaStr);
 		}
 	}
-	env->DeleteLocalRef(cls);
 	return array;
 }
 
diff --git a/jni/NativeFormats/util/AndroidUtil.h b/jni/NativeFormats/util/AndroidUtil.h
index 391967227..79fff5a19 100644
--- a/jni/NativeFormats/util/AndroidUtil.h
+++ b/jni/NativeFormats/util/AndroidUtil.h
@@ -27,6 +27,7 @@
 
 #include <shared_ptr.h>
 
+class JavaClass;
 class VoidMethod;
 class IntMethod;
 class LongMethod;
@@ -44,7 +45,7 @@ private:
 	static JavaVM *ourJavaVM;
 
 public:
-	static const char * const Class_java_lang_String;
+	static shared_ptr<JavaClass> Class_java_lang_String;
 	static const char * const Class_java_util_Collection;
 	static const char * const Class_java_util_Locale;
 	static const char * const Class_java_io_InputStream;
diff --git a/jni/NativeFormats/util/JniEnvelope.cpp b/jni/NativeFormats/util/JniEnvelope.cpp
index 2d7daf718..1d4e03320 100644
--- a/jni/NativeFormats/util/JniEnvelope.cpp
+++ b/jni/NativeFormats/util/JniEnvelope.cpp
@@ -23,12 +23,28 @@
 
 static const std::string JNI_LOGGER_CLASS = "JniLog";
 
+JavaClass::JavaClass(JNIEnv *env, const std::string &name) : myName(name), myEnv(env) {
+	jclass ref = env->FindClass(name.c_str());
+	myClass = (jclass)env->NewGlobalRef(ref);
+	env->DeleteLocalRef(ref);
+}
+
+JavaClass::~JavaClass() {
+	myEnv->DeleteGlobalRef(myClass);
+}
+
 Method::Method(JNIEnv *env, jclass cls, const std::string &name, const std::string &signature) : myName(name) {
 	//ZLLogger::Instance().registerClass(JNI_LOGGER_CLASS);
 	myEnv = env;
 	myId = env->GetMethodID(cls, name.c_str(), signature.c_str());
 }
 
+Method::Method(const JavaClass &cls, const std::string &name, const std::string &signature) : myName(name) {
+	//ZLLogger::Instance().registerClass(JNI_LOGGER_CLASS);
+	myEnv = cls.myEnv;
+	myId = myEnv->GetMethodID(cls.myClass, name.c_str(), signature.c_str());
+}
+
 Method::~Method() {
 }
 
@@ -95,6 +111,9 @@ jboolean BooleanMethod::call(jobject base, ...) {
 StringMethod::StringMethod(JNIEnv *env, jclass cls, const std::string &name, const std::string &signature) : Method(env, cls, name, signature + "Ljava/lang/String;") {
 }
 
+StringMethod::StringMethod(const JavaClass &cls, const std::string &name, const std::string &signature) : Method(cls, name, signature + "Ljava/lang/String;") {
+}
+
 jstring StringMethod::call(jobject base, ...) {
 	ZLLogger::Instance().println(JNI_LOGGER_CLASS, "calling StringMethod " + myName);
 	va_list lst;
diff --git a/jni/NativeFormats/util/JniEnvelope.h b/jni/NativeFormats/util/JniEnvelope.h
index 41492a057..16fbe0c5e 100644
--- a/jni/NativeFormats/util/JniEnvelope.h
+++ b/jni/NativeFormats/util/JniEnvelope.h
@@ -24,12 +24,37 @@
 
 #include <string>
 
+class JavaClass {
+
+public:
+	JavaClass(JNIEnv *env, const std::string &name);
+	~JavaClass();
+	jclass j();
+
+private:
+	JavaClass(const JavaClass&);
+	const JavaClass &operator = (const JavaClass&);
+
+private:
+	const std::string myName;
+	JNIEnv *myEnv;
+	jclass myClass;
+
+friend class Method;
+friend class StaticMethod;
+};
+
 class Method {
 
 public:
 	Method(JNIEnv *env, jclass cls, const std::string &name, const std::string &signature);
+	Method(const JavaClass &cls, const std::string &name, const std::string &signature);
 	virtual ~Method();
 
+private:
+	Method(const Method&);
+	const Method &operator = (const Method&);
+
 protected:
 	const std::string myName;
 	JNIEnv *myEnv;
@@ -42,6 +67,10 @@ public:
 	StaticMethod(JNIEnv *env, jclass cls, const std::string &name, const std::string &signature);
 	virtual ~StaticMethod();
 
+private:
+	StaticMethod(const StaticMethod&);
+	const StaticMethod &operator = (const StaticMethod&);
+
 protected:
 	const std::string myName;
 	JNIEnv *myEnv;
@@ -79,6 +108,7 @@ public:
 class StringMethod : public Method {
 
 public:
+	StringMethod(const JavaClass &cls, const std::string &name, const std::string &signature);
 	StringMethod(JNIEnv *env, jclass cls, const std::string &name, const std::string &signature);
 	jstring call(jobject base, ...);
 };
@@ -97,4 +127,6 @@ public:
 	jobject call(jclass cls, ...);
 };
 
+inline jclass JavaClass::j() { return myClass; }
+
 #endif /* __JNIENVELOPE_H__ */