JNI object meta loader

example.cpp

/*
Copyright 2017 Sergey Bubenshchikov (Sergey.V.Bubenshchikov@gmail.com)

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

void test(JNIEnv * env, jobject j_matrix_object){
    const char* class_name = "my/package/name/MatrixClass",
                constructor_signature = "([[B)V",
                method_name = "getData",
                method_signature = "()[[B";
    // load class meta
    JObjectMeta* matrixContainer = JObjectMeta::loadInfo(
                    env, 
                    class_name, constructor_signature, 
                    method_name, method_signature
                    /*
                    method_name1, method_signature1,
                    method_name2, method_signature2,
                    etc...
                    */
                );
    // call method
    jobject dsId = env->CallIntMethod(j_matrix_object, dsPrototype->methods->at(method_name));
}

JObjectMeta.cpp

/*
Copyright 2017 Sergey Bubenshchikov (Sergey.V.Bubenshchikov@gmail.com)

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

#include "JObjectPrototype.h"
#include <stdarg.h>

JObjectMeta::JObjectMeta(jclass j_class, jmethodID j_methodId, map<const char*, jmethodID>* initMethods) 
	: cls(j_class), constructor(j_methodId), methods(initMethods)
{
}

JObjectMeta::~JObjectMeta()
{
	if (methods)
		delete methods;
}

JObjectMeta * JObjectMeta::loadInfo(JNIEnv * env, const char * clsName, const char * constructorSignature,
	int methodsCount, ...)
{
	// load class by name
	jclass cls = env->FindClass(clsName);
	if (env->ExceptionOccurred())
		return NULL;

	// take constructor by signature
	jmethodID constructorId;
	if(constructorSignature){
		constructorId = env->GetMethodID(cls, "<init>", constructorSignature);
		if (env->ExceptionOccurred())
			return NULL;
	} else
		constructorId = NULL;

	map<const char*, jmethodID>* initMethods = NULL;
	if (methodsCount) {
		initMethods = new map<const char*, jmethodID>();
		// method name and signature inside of array
		methodsCount *= 2;
		va_list ap;
		va_start(ap, methodsCount);
		for (int i = 0; i < methodsCount; i+=2)
		{
			const char *methodName = va_arg(ap, const char*),
						*methodSignature = va_arg(ap, const char*);

			jmethodID methodId = env->GetMethodID(cls, methodName, methodSignature);
			// is method found
			if (env->ExceptionOccurred()) {
				initMethods->clear();
				// take an exception class with custom message
				env->ExceptionClear();
				jclass exClass = env->FindClass("java/lang/NoSuchMethodError");
				if (env->ExceptionOccurred())
					// ACHTUNG! we haven't base classes
					return NULL;
				// create custom message
				char* message = new char[22 + strlen(methodName) + 20 + strlen(methodSignature) + 10 + strlen(clsName) + 1];
				strcpy_s(message, 22, "Unable to find method ");
				strcat_s(message, strlen(methodName), methodName);
				strcat_s(message, 20, " with JNI signature ");
				strcat_s(message, strlen(methodSignature), methodSignature);
				strcat_s(message, 10, " at class ");
				strcat_s(message, strlen(clsName), clsName);
				strcat_s(message, 1, "\0");
				env->ThrowNew(exClass, message);

				delete[] message;
				delete initMethods;
				return NULL;
			}

			(*initMethods)[methodName] = methodId;
		}
	}

	return new JObjectMeta(cls, constructorId, initMethods);
}

JObjectMeta.h

/*
Copyright 2017 Sergey Bubenshchikov (Sergey.V.Bubenshchikov@gmail.com)

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

#pragma once
#include <jni.h>
#include <map>

using namespace std;

class JObjectMeta
{
	JObjectMeta(jclass, jmethodID, map<const char*, jmethodID>*);

public:

	~JObjectMeta();

	const jclass cls;
	const jmethodID constructor;

	const map<const char*, jmethodID>* const methods;

	static JObjectMeta* loadInfo(JNIEnv * env, const char* clsName, const char* constructorSignature, int methodsCount = 0, ...);
};