1、Java String 轉(zhuǎn) C++ String / C++ char*

//C++string 需要導(dǎo)入 #include <string>頭文件
// jstring jValue 是從java層傳入懊悯，或者通過javaBean對(duì)象的屬性值獲取
std::string strValue;
const char *cstr = env->GetStringUTFChars(jValue, NULL); //轉(zhuǎn)成C++ char*
strValue = std::string(cstr);
jniEnv->ReleaseStringUTFChars(jValue, cstr);

// 例如 javabean 中有dataPath 屬性幽勒，現(xiàn)獲取javaBean對(duì)象的dataPath值桨昙，轉(zhuǎn)成C++ string
#include <jni.h>
#include <string>
/*
** obj : java Bean 的對(duì)象
**/
std::string ShapeParamsJniData::GetDataPathValue(jobject obj) {

    int attach = 0;
    JNIEnv *jniEnv = GetAttachEnv(&attach);
    if (jniEnv == NULL) {
        return 0;
    }
    jstring jValue = static_cast<jstring>(jniEnv->GetObjectField(obj,ShapeJniData::dataPathFieldId));
    std::string strValue;
    if (jValue != nullptr) {
        const char *cstr = jniEnv->GetStringUTFChars(jValue, NULL); //轉(zhuǎn)成C++ char*
        strValue = std::string(cstr);
        jniEnv->ReleaseStringUTFChars(jValue, cstr);
    }
    if (attach) {
        DetachEnv();
    }

    return strValue;
}

2骡楼、 java 浮點(diǎn)型數(shù)組 轉(zhuǎn) C++ 浮點(diǎn)型數(shù)組

/**
* dataObj 是java Bean對(duì)象，m_matsFieldId 是屬性 float[] mats;
**/
jfloatArray matArr = static_cast<jfloatArray>(env->GetObjectField(dataObj, m_matsFieldId));
 
 jint matLen = env->GetArrayLength(matArr);
 //在C/C++中創(chuàng)建一個(gè)緩存區(qū)赴肚，然后將Java中的原始數(shù)組拷貝到緩沖區(qū)中去
//strData 是C++ 結(jié)構(gòu)體的聲明 素跺，strData.m_mat4 是結(jié)構(gòu)體 float[]類型成員
 env->GetFloatArrayRegion(matArr,0,matLen,strData.m_mat4); 

3、 Java對(duì)象數(shù)組 -> C++ 結(jié)構(gòu)體指針數(shù)組

// obj 是javaBean 對(duì)象誉券，touchPointsFieldId是該對(duì)象的 類型是 object[]
jobjectArray pointArr = static_cast<jobjectArray>(env->GetObjectField(obj,touchPointsFieldId));

// 通過GetArrayLength方法獲取數(shù)組大小
jsize size = env->GetArrayLength(pointArr); 

// pTouchPoint 指厌，C++ 的結(jié)構(gòu)體指針，
//注意：使用new申請(qǐng)的空間需要在方法外 delete[]
TouchPoint* pTouchPoint = new TouchPoint[size]; 

for (int i = 0; i < size; i++){
       // 通過 GetObjectArrayElement 獲取元素
        jobject touchPointObj = env->GetObjectArrayElement(pointArr,i);
       // GetAllValue 方法是封裝 轉(zhuǎn) 屬性 值的
        TouchPoint touchPoint = TouchPointJniData::GetAllValue(touchPointObj); 
        pTouchPoint[i] = touchPoint;
  }

4踊跟、 Java List -> C++ Map

extern "C"
JNIEXPORT void JNICALL
Java_com_engine_operate_edit_initListId(JNIEnv *env, jclass clazz) {
   
    jclass clz = env->FindClass("java/util/ArrayList");
    ListJniData::clz = static_cast<jclass>(env->NewGlobalRef(clz));

    ListJniData::listInitMethodId = env->GetMethodID(clz,"<init>", "()V");
    ListJniData::listAddMethodId = env->GetMethodID(clz,"add", "(Ljava/lang/Object;)Z");
    ListJniData::listGetMethodId = env->GetMethodID(clz,"get", "(I)Ljava/lang/Object;");
    ListJniData::listSizeMethodId = env->GetMethodID(clz,"size", "()I");
}

void SelectLimitJniData::GetTypeParamListValue(jobject obj, SelectLimit *selectLimit)  {

    int attach = 0;
    JNIEnv *env = GetAttachEnv(&attach);
    if (env == NULL){
        return;
    }
    map<PenType, float> minMaps;
    map<PenType, float> maxMaps;

    jobject listParams = env->GetObjectField(obj,SelectLimitJniData::penTypeParamListFieldId);
    if (listParams != nullptr){
        jint size = env->CallIntMethod(listParams,ListJniData::listSizeMethodId);
        for (int i = 0; i < size; i++){
           jobject param = env->CallObjectMethod(listParams,ListJniData::listGetMethodId,i);
            if (param == nullptr){
                continue;
            }
            jint type = env->GetIntField(param,SelectLimitJniData::penTypeFieldId);
            PenType penType = static_cast<PenType>(type);
            jfloat maxPenSize = env->GetFloatField(param,SelectLimitJniData::maxPenSizeFieldId);
            jfloat minPenSize = env->GetFloatField(param,SelectLimitJniData::minPenSizeFieldId);

            minMaps[penType] = minPenSize;
            maxMaps[penType] = maxPenSize;
        }
        selectLimit->minSizeMap = minMaps;
        selectLimit->maxSizeMap = maxMaps;
    }

    if (attach){
        DetachEnv();
    }
}