Android jni 在C++代码中给HashMap＜Integer, ArrayList＜String＞＞类型的参数赋值

本文链接：https://blog.youkuaiyun.com/tranquality_c/article/details/125917748

这篇博客详细记录了如何在C++中使用JNI技术向HashMap<Integer, ArrayList<myStruct>>插入数据的过程，包括对Java对象的创建、方法调用等步骤。同时，还介绍了如何通过StringBuffer实现Java中String类型的引用传递，以便在C++中进行修改和赋值操作。示例代码清晰展示了整个流程。

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最近项目中有部分需求需要给Android端实现部分功能，以jni方式实现，对此方式不是很熟悉，浅浅地记录一下当参数类型为HashMap<Integer, ArrayList>时，该如何在C++中向此容器插入数据的问题.
代码片段如下

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_myProject_XXNative_myFun(JNIEnv *env, jclass clazz, jobject desMap)
{
	//...
	std::map<int, std::vector<myStruct>> srcMap;
	std::map<int, std::vector<myStruct>>::iterator iter = srcMap.begin();
    for(; iter != srcMap.end(); iter++)
    {
        int nKey = iter->first;
        jclass integerClass = env->FindClass("java/lang/Integer");
        jmethodID integerConstructorID = env->GetMethodID(integerClass, "<init>", "(I)V");
        jobject key = env->NewObject(integerClass, integerConstructorID, nKey);
        std::vector<myStruct> srcVec = iter->second;
        int nSize = srcVec.size();
        jclass mapClass = env->FindClass("java/util/HashMap");
        jmethodID putMethodID =
                env->GetMethodID(
                        mapClass,
                        "put",
                        "(Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;" );

        jclass arrayListClass = env->FindClass("java/util/ArrayList");
        jmethodID arrayListInit = env->GetMethodID(arrayListClass, "<init>", "()V");
        jmethodID addToList = env->GetMethodID(
                arrayListClass,
                "add",
                "(Ljava/lang/Object;)Z" );
        jobject listObj = env->NewObject(arrayListClass, arrayListInit);
        for(int i = 0; i < nPaperSize; i++)
        {
            myStruct tObj = srcVec.at(i);
            jstring firstStr = str2jstring(env, tObj.firstStr.c_str());
            jstring secondStr = str2jstring(env, tObj.secondStr.c_str());
            env->CallBooleanMethod(listObj, addToList, firstStr);
            env->CallBooleanMethod(listObj, addToList, secondStr);
            env->DeleteLocalRef(firstStr);
            env->DeleteLocalRef(secondStr);
        }
        env->CallObjectMethod(papers_map, putMethodID, key, listObj);
        //资源释放
        env->DeleteLocalRef(integerClass);
        env->DeleteLocalRef(key);
        env->DeleteLocalRef(mapClass);
        env->DeleteLocalRef(arrayListClass);
        env->DeleteLocalRef(listObj);
    }
}

顺便一提，如果参数中想以引用传递方式传java中的String类型（传到C++方法中修改赋值），可以用StringBuffer实现
代码片段如下

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_myProject_XXNative_myFun(JNIEnv *env, jclass clazz, jobject str_id)
{
	std::string strId;
    jstring jstrId = env->NewStringUTF(strId.c_str());
    jclass stringBufferClass = env->FindClass("java/lang/StringBuffer");
    jmethodID appendMethodID =
            env->GetMethodID(
                    stringBufferClass,
                    "append",
                    "(Ljava/lang/Object;)Ljava/lang/StringBuffer;" );
    env->CallObjectMethod(str_id, appendMethodID, jstrId);
    //资源释放
    env->DeleteLocalRef(jstrId);
    env->DeleteLocalRef(stringBufferClass);
}