diff --git a/jni/NativeFormats/JavaPluginCollection.cpp b/jni/NativeFormats/JavaPluginCollection.cpp
index 8905aba6b..016c6ccc1 100644
--- a/jni/NativeFormats/JavaPluginCollection.cpp
+++ b/jni/NativeFormats/JavaPluginCollection.cpp
@@ -17,11 +17,10 @@
  * 02110-1301, USA.
  */
 
-#include <jni.h>
-
 #include <vector>
 
 #include <AndroidUtil.h>
+#include <JniEnvelope.h>
 
 #include "fbreader/src/formats/FormatPlugin.h"
 
@@ -29,18 +28,17 @@ extern "C"
 JNIEXPORT jobjectArray JNICALL Java_org_geometerplus_fbreader_formats_PluginCollection_nativePlugins(JNIEnv* env, jobject thiz) {
 	const std::vector<shared_ptr<FormatPlugin> > plugins = PluginCollection::Instance().plugins();
 	const size_t size = plugins.size();
-	jclass cls = env->FindClass(AndroidUtil::Class_NativeFormatPlugin);
+	jclass cls = AndroidUtil::Class_NativeFormatPlugin->j();
 	// TODO: memory leak?
 	jobjectArray javaPlugins = env->NewObjectArray(size, cls, 0);
 
 	for (size_t i = 0; i < size; ++i) {
 		jstring fileType = AndroidUtil::createJavaString(env, plugins[i]->supportedFileType());
-		jobject p = env->NewObject(cls, AndroidUtil::MID_NativeFormatPlugin_init, fileType);
+		jobject p = AndroidUtil::Constructor_NativeFormatPlugin->call(fileType);
 		env->SetObjectArrayElement(javaPlugins, i, p);
 		env->DeleteLocalRef(p);
 		env->DeleteLocalRef(fileType);
 	}
-	env->DeleteLocalRef(cls);
 	return javaPlugins;
 }
 
diff --git a/jni/NativeFormats/util/AndroidUtil.cpp b/jni/NativeFormats/util/AndroidUtil.cpp
index b8ee0f5ab..0a46e41eb 100644
--- a/jni/NativeFormats/util/AndroidUtil.cpp
+++ b/jni/NativeFormats/util/AndroidUtil.cpp
@@ -30,14 +30,14 @@ const char * const AndroidUtil::Class_java_util_Collection = "java/util/Collecti
 const char * const AndroidUtil::Class_java_util_Locale = "java/util/Locale";
 const char * const AndroidUtil::Class_java_io_InputStream = "java/io/InputStream";
 const char * const AndroidUtil::Class_ZLibrary = "org/geometerplus/zlibrary/core/library/ZLibrary";
-const char * const AndroidUtil::Class_NativeFormatPlugin = "org/geometerplus/fbreader/formats/NativeFormatPlugin";
+shared_ptr<JavaClass> AndroidUtil::Class_NativeFormatPlugin;
 const char * const AndroidUtil::Class_PluginCollection = "org/geometerplus/fbreader/formats/PluginCollection";
 const char * const AndroidUtil::Class_Encoding = "org/geometerplus/zlibrary/core/encodings/Encoding";
 const char * const AndroidUtil::Class_EncodingConverter = "org/geometerplus/zlibrary/core/encodings/EncodingConverter";
 const char * const AndroidUtil::Class_JavaEncodingCollection = "org/geometerplus/zlibrary/core/encodings/JavaEncodingCollection";
 const char * const AndroidUtil::Class_Paths = "org/geometerplus/fbreader/Paths";
 const char * const AndroidUtil::Class_ZLFile = "org/geometerplus/zlibrary/core/filesystem/ZLFile";
-const char * const AndroidUtil::Class_ZLFileImage = "org/geometerplus/zlibrary/core/image/ZLFileImage";
+shared_ptr<JavaClass> AndroidUtil::Class_ZLFileImage;
 const char * const AndroidUtil::Class_Book = "org/geometerplus/fbreader/library/Book";
 const char * const AndroidUtil::Class_Tag = "org/geometerplus/fbreader/library/Tag";
 const char * const AndroidUtil::Class_NativeBookModel = "org/geometerplus/fbreader/bookmodel/NativeBookModel";
@@ -58,7 +58,7 @@ shared_ptr<LongMethod> AndroidUtil::Method_java_io_InputStream_skip;
 shared_ptr<StaticObjectMethod> AndroidUtil::StaticMethod_ZLibrary_Instance;
 shared_ptr<StringMethod> AndroidUtil::Method_ZLibrary_getVersionName;
 
-jmethodID AndroidUtil::MID_NativeFormatPlugin_init;
+shared_ptr<Constructor> AndroidUtil::Constructor_NativeFormatPlugin;
 shared_ptr<StringMethod> AndroidUtil::Method_NativeFormatPlugin_supportedFileType;
 
 shared_ptr<StaticObjectMethod> AndroidUtil::StaticMethod_PluginCollection_Instance;
@@ -82,7 +82,7 @@ shared_ptr<StringMethod> AndroidUtil::Method_ZLFile_getPath;
 shared_ptr<BooleanMethod> AndroidUtil::Method_ZLFile_isDirectory;
 shared_ptr<LongMethod> AndroidUtil::Method_ZLFile_size;
 
-jmethodID AndroidUtil::MID_ZLFileImage_init;
+shared_ptr<Constructor> AndroidUtil::Constructor_ZLFileImage;
 
 shared_ptr<StaticObjectMethod> AndroidUtil::StaticMethod_Paths_cacheDirectory;
 
@@ -149,10 +149,9 @@ bool AndroidUtil::init(JavaVM* jvm) {
 	Method_ZLibrary_getVersionName = new StringMethod(env, cls, "getVersionName", "()");
 	env->DeleteLocalRef(cls);
 
-	CHECK_NULL( cls = env->FindClass(Class_NativeFormatPlugin) );
-	CHECK_NULL( MID_NativeFormatPlugin_init = env->GetMethodID(cls, "<init>", "(Ljava/lang/String;)V") );
-	Method_NativeFormatPlugin_supportedFileType = new StringMethod(env, cls, "supportedFileType", "()");
-	env->DeleteLocalRef(cls);
+	Class_NativeFormatPlugin = new JavaClass(env, "org/geometerplus/fbreader/formats/NativeFormatPlugin");
+	Constructor_NativeFormatPlugin = new Constructor(*Class_NativeFormatPlugin, "(Ljava/lang/String;)V");
+	Method_NativeFormatPlugin_supportedFileType = new StringMethod(*Class_NativeFormatPlugin, "supportedFileType", "()");
 
 	CHECK_NULL( cls = env->FindClass(Class_PluginCollection) );
 	StaticMethod_PluginCollection_Instance = new StaticObjectMethod(env, cls, "Instance", "org/geometerplus/fbreader/formats/PluginCollection", "()");
@@ -185,9 +184,8 @@ bool AndroidUtil::init(JavaVM* jvm) {
 	Method_ZLFile_size = new LongMethod(env, cls, "size", "()");
 	env->DeleteLocalRef(cls);
 
-	CHECK_NULL( cls = env->FindClass(Class_ZLFileImage) );
-	CHECK_NULL( MID_ZLFileImage_init = env->GetMethodID(cls, "<init>", "(Ljava/lang/String;Lorg/geometerplus/zlibrary/core/filesystem/ZLFile;Ljava/lang/String;II)V") );
-	env->DeleteLocalRef(cls);
+ 	Class_ZLFileImage = new JavaClass(env, "org/geometerplus/zlibrary/core/image/ZLFileImage");
+	Constructor_ZLFileImage = new Constructor(*Class_ZLFileImage, "(Ljava/lang/String;Lorg/geometerplus/zlibrary/core/filesystem/ZLFile;Ljava/lang/String;II)V");
 
 	CHECK_NULL( cls = env->FindClass(Class_Paths) );
 	StaticMethod_Paths_cacheDirectory = new StaticObjectMethod(env, cls, "cacheDirectory", "java/lang/String", "()");
@@ -244,14 +242,11 @@ jobject AndroidUtil::createJavaImage(JNIEnv *env, const ZLFileImage &image) {
 	jobject javaFile = createJavaFile(env, image.file().path());
 	jstring javaEncoding = createJavaString(env, image.encoding());
 
-	jclass cls = env->FindClass(Class_ZLFileImage);
-	jobject javaImage = env->NewObject(
-		cls, MID_ZLFileImage_init,
+	jobject javaImage = Constructor_ZLFileImage->call(
 		javaMimeType, javaFile, javaEncoding,
 		image.offset(), image.size()
 	);
 
-	env->DeleteLocalRef(cls);
 	env->DeleteLocalRef(javaEncoding);
 	env->DeleteLocalRef(javaFile);
 	env->DeleteLocalRef(javaMimeType);
diff --git a/jni/NativeFormats/util/AndroidUtil.h b/jni/NativeFormats/util/AndroidUtil.h
index 1d3bb20c9..7cbe7c467 100644
--- a/jni/NativeFormats/util/AndroidUtil.h
+++ b/jni/NativeFormats/util/AndroidUtil.h
@@ -28,6 +28,7 @@
 #include <shared_ptr.h>
 
 class JavaClass;
+class Constructor;
 class VoidMethod;
 class IntMethod;
 class LongMethod;
@@ -51,8 +52,8 @@ public:
 	static const char * const Class_java_io_InputStream;
 	static const char * const Class_ZLibrary;
 	static const char * const Class_ZLFile;
-	static const char * const Class_ZLFileImage;
-	static const char * const Class_NativeFormatPlugin;
+	static shared_ptr<JavaClass> Class_ZLFileImage;
+	static shared_ptr<JavaClass> Class_NativeFormatPlugin;
 	static const char * const Class_PluginCollection;
 	static const char * const Class_Encoding;
 	static const char * const Class_EncodingConverter;
@@ -86,9 +87,9 @@ public:
 	static shared_ptr<BooleanMethod> Method_ZLFile_isDirectory;
 	static shared_ptr<LongMethod> Method_ZLFile_size;
 
-	static jmethodID MID_ZLFileImage_init;
+	static shared_ptr<Constructor> Constructor_ZLFileImage;
 
-	static jmethodID MID_NativeFormatPlugin_init;
+	static shared_ptr<Constructor> Constructor_NativeFormatPlugin;
 	static shared_ptr<StringMethod> Method_NativeFormatPlugin_supportedFileType;
 
 	static shared_ptr<StaticObjectMethod> StaticMethod_PluginCollection_Instance;
diff --git a/jni/NativeFormats/util/JniEnvelope.cpp b/jni/NativeFormats/util/JniEnvelope.cpp
index 1d4e03320..2b2a029fa 100644
--- a/jni/NativeFormats/util/JniEnvelope.cpp
+++ b/jni/NativeFormats/util/JniEnvelope.cpp
@@ -33,6 +33,18 @@ JavaClass::~JavaClass() {
 	myEnv->DeleteGlobalRef(myClass);
 }
 
+Constructor::Constructor(const JavaClass &cls, const std::string &signature) : myClass(cls) {
+	myId = cls.myEnv->GetMethodID(cls.j(), "<init>", signature.c_str());
+}
+
+jobject Constructor::call(...) {
+	va_list lst;
+	va_start(lst, this);
+	jobject obj = myClass.myEnv->NewObjectV(myClass.j(), myId, lst);
+	va_end(lst);
+	return obj;
+}
+
 Method::Method(JNIEnv *env, jclass cls, const std::string &name, const std::string &signature) : myName(name) {
 	//ZLLogger::Instance().registerClass(JNI_LOGGER_CLASS);
 	myEnv = env;
diff --git a/jni/NativeFormats/util/JniEnvelope.h b/jni/NativeFormats/util/JniEnvelope.h
index 16fbe0c5e..342f6f107 100644
--- a/jni/NativeFormats/util/JniEnvelope.h
+++ b/jni/NativeFormats/util/JniEnvelope.h
@@ -29,7 +29,7 @@ class JavaClass {
 public:
 	JavaClass(JNIEnv *env, const std::string &name);
 	~JavaClass();
-	jclass j();
+	jclass j() const;
 
 private:
 	JavaClass(const JavaClass&);
@@ -42,6 +42,22 @@ private:
 
 friend class Method;
 friend class StaticMethod;
+friend class Constructor;
+};
+
+class Constructor {
+
+public:
+	Constructor(const JavaClass &cls, const std::string &signature);
+	jobject call(...);
+
+private:
+	Constructor(const Constructor&);
+	const Constructor &operator = (const Constructor&);
+
+protected:
+	const JavaClass &myClass;
+	jmethodID myId;
 };
 
 class Method {
@@ -127,6 +143,6 @@ public:
 	jobject call(jclass cls, ...);
 };
 
-inline jclass JavaClass::j() { return myClass; }
+inline jclass JavaClass::j() const { return myClass; }
 
 #endif /* __JNIENVELOPE_H__ */