jni 提取 assets 目录下的文件

传入参数 ：
ctx = context
dir = 文件路径
szDexPath = ......jiami.dat
fileName = jiami.dat

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <android/asset_manager.h>
#include <android/asset_manager_jni.h>

int extract_file(JNIEnv* env, jobject ctx, const char* dir,const char* szDexPath,const char* fileName)
{

    if (access(dir, F_OK) !=0) {        // 判断 这两个路径、文件是否存在
        mkdir(dir, 505);
        chmod(dir, 505);
    }

    if (access(szDexPath,F_OK)==0) {
      LOGD("[+]File %s have existed",szDexPath);
        return 0;
    }
    //jiami.dat不存在，开始提取
    else {
        AAssetManager* mgr;
        jclass ApplicationClass = env->GetObjectClass(ctx);
        jmethodID getAssets = env->GetMethodID(ApplicationClass, "getAssets", "()Landroid/content/res/AssetManager;");
        jobject Assets_obj = env->CallObjectMethod(ctx, getAssets);
        mgr = AAssetManager_fromJava(env, Assets_obj);      // 获取 AssetManager 对象
        if (mgr == NULL) {
            LOGE("[-]getAAssetManager failed");
            return 0;
        }
        AAsset* asset = AAssetManager_open(mgr, fileName, AASSET_MODE_STREAMING);   // 获取 asset 对象，对应的文件名    UNKNOWN 0, RANDOM 1, STREAMING 2, BUFFER 3
        FILE* file = fopen(szDexPath, "wb");        // wb 只写打开或新建一个二进制文件；只允许写数据
        int bufferSize = AAsset_getLength(asset);       // 长度
        LOGD("[+]Asset FileName:%s,extract path:%s,size:%d\n",fileName,szDexPath, bufferSize);      // Asset FileName:jiami.dat, extract path:/data/data/com.wangwz.ndk_test/files/.jiagu/jiami.dat, size:2639568
        void* buffer =malloc(4096);
        while (true) {
            int numBytesRead = AAsset_read(asset, buffer, 4096);
            if (numBytesRead <= 0)
                break;
            fwrite(buffer, numBytesRead, 1, file);      // 写入到 file 内
        }
        free(buffer);
        fclose(file);
        AAsset_close(asset);
        chmod(szDexPath, 493);
    }
}