cocos2d-x引擎对jni的操作进行了封装，提供了一个非常好用的类:JniHelper，定义了一些常用的接口，该文件位于cocos/platform/android/jni目录下。

下面是源码：

/****************************************************************************
Copyright (c) 2010-2012 cocos2d-x.org
Copyright (c) 2013-2014 Chukong Technologies Inc.

http://www.cocos2d-x.org

Permission is hereby granted,free of charge,to any person obtaining a copy
of this software and associated documentation files (the "Software"),to deal
in the Software without restriction,including without limitation the rights
to use,copy,modify,merge,publish,distribute,sublicense,and/or sell
copies of the Software,and to permit persons to whom the Software is
furnished to do so,subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS",WITHOUT WARRANTY OF ANY KIND,EXPRESS OR
IMPLIED,INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,DAMAGES OR OTHER
LIABILITY,WHETHER IN AN ACTION OF CONTRACT,TORT OR OTHERWISE,ARISING FROM,OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
****************************************************************************/
#ifndef __ANDROID_JNI_HELPER_H__
#define __ANDROID_JNI_HELPER_H__

#include <jni.h>
#include <string>
#include "platform/CCPlatformMacros.h"

NS_CC_BEGIN

typedef struct JniMethodInfo_//这个结构体包含了JNI运行环境、调用的方法所在的类、以及调用的方法名
{
    JNIEnv *    env;
    jclass      classID;
    jmethodID   methodID;
} JniMethodInfo;

class CC_DLL JniHelper
{
public:
    static void setJavaVM(JavaVM *javaVM);
    static JavaVM* getJavaVM();
    static JNIEnv* getEnv();

    static bool setClassLoaderFrom(jobject activityInstance);
    static bool getStaticMethodInfo(JniMethodInfo &methodinfo,const char *className,const char *methodName,const char *paramCode);
    static bool getMethodInfo(JniMethodInfo &methodinfo,const char *paramCode);

    static std::string jstring2string(jstring str);

    static jmethodID loadclassMethod_methodID;
    static jobject classloader;

private:
    static JNIEnv* cacheEnv(JavaVM* jvm);

    static bool getMethodInfo_DefaultClassLoader(JniMethodInfo &methodinfo,const char *paramCode);

    static JavaVM* _psJavaVM;
};

NS_CC_END

#endif // __ANDROID_JNI_HELPER_H__

/****************************************************************************
Copyright (c) 2010-2012 cocos2d-x.org
Copyright (c) 2013-2014 Chukong Technologies Inc.

http://www.cocos2d-x.org

Permission is hereby granted,OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
****************************************************************************/
#include "JniHelper.h"
#include <android/log.h>
#include <string.h>
#include <pthread.h>

#define  LOG_TAG    "JniHelper"
#define  LOGD(...)  __android_log_print(ANDROID_LOG_DEBUG,LOG_TAG,__VA_ARGS__)
#define  LOGE(...)  __android_log_print(ANDROID_LOG_ERROR,__VA_ARGS__)

static pthread_key_t g_key;

jclass _getClassID(const char *className) {
    if (nullptr == className) {
        return nullptr;
    }

    JNIEnv* env = cocos2d::JniHelper::getEnv();

    jstring _jstrClassName = env->NewStringUTF(className);

    jclass _clazz = (jclass) env->CallObjectMethod(cocos2d::JniHelper::classloader,cocos2d::JniHelper::loadclassMethod_methodID,_jstrClassName);

    if (nullptr == _clazz) {
        LOGE("Classloader Failed to find class of %s",className);
        env->ExceptionClear();
    }

    env->DeleteLocalRef(_jstrClassName);
        
    return _clazz;
}

void _detachCurrentThread(void* a) {
    cocos2d::JniHelper::getJavaVM()->DetachCurrentThread();
}

namespace cocos2d {

    JavaVM* JniHelper::_psJavaVM = nullptr;
    jmethodID JniHelper::loadclassMethod_methodID = nullptr;
    jobject JniHelper::classloader = nullptr;

    JavaVM* JniHelper::getJavaVM() {
        pthread_t thisthread = pthread_self();
        LOGD("JniHelper::getJavaVM(),pthread_self() = %ld",thisthread);
        return _psJavaVM;
    }

    void JniHelper::setJavaVM(JavaVM *javaVM) {
        pthread_t thisthread = pthread_self();
        LOGD("JniHelper::setJavaVM(%p),javaVM,thisthread);
        _psJavaVM = javaVM;

        pthread_key_create(&g_key,_detachCurrentThread);
    }

    JNIEnv* JniHelper::cacheEnv(JavaVM* jvm) {
        JNIEnv* _env = nullptr;
        // get jni environment
        jint ret = jvm->GetEnv((void**)&_env,JNI_VERSION_1_4);
        
        switch (ret) {
        case JNI_OK :
            // Success!
            pthread_setspecific(g_key,_env);
            return _env;
                
        case JNI_EDETACHED :
            // Thread not attached
            if (jvm->AttachCurrentThread(&_env,nullptr) < 0)
                {
                    LOGE("Failed to get the environment using AttachCurrentThread()");

                    return nullptr;
                } else {
                // Success : Attached and obtained JNIEnv!
                pthread_setspecific(g_key,_env);
                return _env;
            }
                
        case JNI_EVERSION :
            // Cannot recover from this error
            LOGE("JNI interface version 1.4 not supported");
        default :
            LOGE("Failed to get the environment using GetEnv()");
            return nullptr;
        }
    }

    JNIEnv* JniHelper::getEnv() {
        JNIEnv *_env = (JNIEnv *)pthread_getspecific(g_key);
        if (_env == nullptr)
            _env = JniHelper::cacheEnv(_psJavaVM);
        return _env;
    }

    bool JniHelper::setClassLoaderFrom(jobject activityinstance) {
        JniMethodInfo _getclassloaderMethod;
        if (!JniHelper::getMethodInfo_DefaultClassLoader(_getclassloaderMethod,"android/content/Context","getClassLoader","()Ljava/lang/ClassLoader;")) {
            return false;
        }

        jobject _c = cocos2d::JniHelper::getEnv()->CallObjectMethod(activityinstance,_getclassloaderMethod.methodID);

        if (nullptr == _c) {
            return false;
        }

        JniMethodInfo _m;
        if (!JniHelper::getMethodInfo_DefaultClassLoader(_m,"java/lang/ClassLoader","loadClass","(Ljava/lang/String;)Ljava/lang/Class;")) {
            return false;
        }

        JniHelper::classloader = cocos2d::JniHelper::getEnv()->NewGlobalRef(_c);
        JniHelper::loadclassMethod_methodID = _m.methodID;

        return true;
    }

    bool JniHelper::getStaticMethodInfo(JniMethodInfo &methodinfo,const char *paramCode) {
        if ((nullptr == className) ||
            (nullptr == methodName) ||
            (nullptr == paramCode)) {
            return false;
        }

        JNIEnv *env = JniHelper::getEnv();
        if (!env) {
            LOGE("Failed to get JNIEnv");
            return false;
        }
            
        jclass classID = _getClassID(className);
        if (! classID) {
            LOGE("Failed to find class %s",className);
            env->ExceptionClear();
            return false;
        }

        jmethodID methodID = env->GetStaticMethodID(classID,methodName,paramCode);
        if (! methodID) {
            LOGE("Failed to find static method id of %s",methodName);
            env->ExceptionClear();
            return false;
        }
            
        methodinfo.classID = classID;
        methodinfo.env = env;
        methodinfo.methodID = methodID;
        return true;
    }

    bool JniHelper::getMethodInfo_DefaultClassLoader(JniMethodInfo &methodinfo,const char *paramCode) {
        if ((nullptr == className) ||
            (nullptr == methodName) ||
            (nullptr == paramCode)) {
            return false;
        }

        JNIEnv *env = JniHelper::getEnv();
        if (!env) {
            return false;
        }

        jclass classID = env->FindClass(className);
        if (! classID) {
            LOGE("Failed to find class %s",className);
            env->ExceptionClear();
            return false;
        }

        jmethodID methodID = env->GetMethodID(classID,paramCode);
        if (! methodID) {
            LOGE("Failed to find method id of %s",methodName);
            env->ExceptionClear();
            return false;
        }

        methodinfo.classID = classID;
        methodinfo.env = env;
        methodinfo.methodID = methodID;

        return true;
    }

    bool JniHelper::getMethodInfo(JniMethodInfo &methodinfo,const char *paramCode) {
        if ((nullptr == className) ||
            (nullptr == methodName) ||
            (nullptr == paramCode)) {
            return false;
        }

        JNIEnv *env = JniHelper::getEnv();
        if (!env) {
            return false;
        }

        jclass classID = _getClassID(className);
        if (! classID) {
            LOGE("Failed to find class %s",methodName);
            env->ExceptionClear();
            return false;
        }

        methodinfo.classID = classID;
        methodinfo.env = env;
        methodinfo.methodID = methodID;

        return true;
    }

    std::string JniHelper::jstring2string(jstring jstr) {
        if (jstr == nullptr) {
            return "";
        }
        
        JNIEnv *env = JniHelper::getEnv();
        if (!env) {
            return nullptr;
        }

        const char* chars = env->GetStringUTFChars(jstr,nullptr);
        std::string ret(chars);
        env->ReleaseStringUTFChars(jstr,chars);

        return ret;
    }

} //namespace cocos2d

1、getStaticMethodInfo：

用于调用Java类的非静态函数

3、CallStaticVoidMethod

void JniFun::longinWX(const char* APP_ID,const char* AppSecret)
	{
#if CC_TARGET_PLATFORM == CC_PLATFORM_ANDROID
		JniMethodInfo minfo;
		bool isHave = JniHelper::getStaticMethodInfo(minfo,JAVA_CLASSNAME,"LoginWX","(Ljava/lang/String;Ljava/lang/String;)V");
		if (isHave)
		{
			jstring jAPP_ID = minfo.env->NewStringUTF(APP_ID);										 
			jstring jAppSecret = minfo.env->NewStringUTF(AppSecret);
			minfo.env->CallStaticVoidMethod(minfo.classID,minfo.methodID,jAPP_ID,jAppSecret);

			minfo.env->DeleteLocalRef(jAPP_ID);
			minfo.env->DeleteLocalRef(jAppSecret);
			minfo.env->DeleteLocalRef(minfo.classID); 
			cocos2d::log("JniFun call LoginWX over!");
		}
		else
		{
			//NoticeMsg::Instance().Showlogon(false);
			cocos2d::log("JniFun call LoginWX error!");
		}
#endif
#if CC_TARGET_PLATFORM == CC_PLATFORM_IOS
        cocos2d::log("IosHelper::sendAuthRequest!");
		IosHelper::sendAuthRequest();
#endif
	}