jni读取assets资源文件

assets目录底下的文件会被打包到一个apk文件里，这些资源在安装时他们并没被解压,使用时是直接从apk中读取的。这里介绍下怎么在jni内使用ndk自带api的接口函数读取assets资源文件，和libzip库函数的使用，可以用来读创建修改压缩文档，这里也是以读取apk安装包内的资源文件为例。

1 用ndk自带的接口函数读apk包

从2.3开始提供这些接口函数，具体看头文件assert.h android/asset_manager.h android/asset_manager_jni.h，可以参考ndk自带例子中samples/native-audio/ jni/native-audio-jni.c。

/******************************************************************************** Function Name  : java_com_fontlose_ReadAssets_readFromAssets* Description    : 定义：public native void  readFromAssets(AssetManager ass,String filename);* Input          : AssetManager对象 filename资源名* Output         : None* Return         : None*******************************************************************************/ void  Java_com_fontlose_ReadAssets_readFromAssets(JNIEnv* env,jclass tis,jobject assetManager,jstring filename){   LOGI("ReadAssets");    AAssetManager* mgr = AAssetManager_fromJava(env, assetManager);   if(mgr==NULL)   {      LOGI(" %s","AAssetManager==NULL");      return ;   }     /*获取文件名并打开*/   jboolean iscopy;   const char *mfile = (*env)->GetStringUTFChars(env, filename, &iscopy);   AAsset* asset = AAssetManager_open(mgr, mfile,AASSET_MODE_UNKNOWN);   (*env)->ReleaseStringUTFChars(env, filename, mfile);   if(asset==NULL)   {      LOGI(" %s","asset==NULL");      return ;   }   /*获取文件大小*/   off_t bufferSize = AAsset_getLength(asset);   LOGI("file size         : %d\n",bufferSize);   char *buffer=(char *)malloc(bufferSize+1);   buffer[bufferSize]=0;   int numBytesRead = AAsset_read(asset, buffer, bufferSize);   LOGI(": %s",buffer);   free(buffer);    /*关闭文件*/   AAsset_close(asset);}

在应用程序内使用定义和使用如下

public native void  readFromAssets(AssetManager ass,String filename);readFromAssets(getAssets(),"log.txt");

logcat测试结果

12-15 15:27:33.290: INFO/ReadAssets(3570): ReadAssets12-15 15:27:33.290: INFO/ReadAssets(3570): file size         : 13812-15 15:27:33.290: INFO/ReadAssets(3570): : 。。。。。。。。。。。。。。。。12-15 15:27:33.290: INFO/ReadAssets(3570): 这个例子从jni读取assets内文件12-15 15:27:33.290: INFO/ReadAssets(3570): 。。。。。。。。。。。。。。。。

2 使用libzip库读apk包

libzip 使用 C 库来 读创建修改压缩文档，关于libzip在andorid的移植可以参考老外做的android-ndk-assets.zip这个工程，已在NDK下可以编译了，修改下编译生成libzip.so，利用libzip.so和zip.h建立工程，使用libzip还可以读取apk包内其他压缩文件如AndroidManifest.xml布局xml等。

void  Java_com_fontlose_ReadAssets_readFromAssetsLibzip(JNIEnv* env,jclass tis,jstring assetpath,jstring filename){   LOGI("ReadAssets");  int i=0;   jboolean iscopy;   const char *mpath = (*env)->GetStringUTFChars(env, assetpath, &iscopy);   struct zip* apkArchive=zip_open(mpath, 0, NULL);;   (*env)->ReleaseStringUTFChars(env, filename, mpath);   struct zip_stat fstat;   zip_stat_init(&fstat);   int numFiles = zip_get_num_files(apkArchive);   LOGI("File numFiles %i \n",numFiles);   for (i=0; i<numFiles; i++) {     const char* name = zip_get_name(apkArchive, i, 0);        if (name == NULL) {      LOGE("Error reading zip file name at index %i : %s", zip_strerror(apkArchive));      return;    }      zip_stat(apkArchive,name,0,&fstat);    LOGI("File %i:%s Size1: %d Size2: %d", i,fstat.name,fstat.size ,fstat.comp_size)  ;   }   const char *fname = (*env)->GetStringUTFChars(env, filename, &iscopy);   struct zip_file* file = zip_fopen(apkArchive, fname, 0);    if (!file) {     LOGE("Error opening %s from APK", fname);     return;    }   zip_stat(apkArchive,fname,0,&fstat);   (*env)->ReleaseStringUTFChars(env, filename, fname);   char *buffer=(char *)malloc(fstat.size+1);   buffer[fstat.size]=0;   int numBytesRead =  zip_fread(file, buffer,fstat.size);;   LOGI(": %s\n",buffer);   free(buffer);   zip_fclose(file);   zip_close(apkArchive);}

在应用程序内使用定义和使用如下

public native void  readFromAssetsLibzip(String apkpath,String filename); readFromAssetsLibzip(getPackageResourcePath(),"assets/log.txt");

logcat测试结果

12-15 15:28:03.430: INFO/ReadAssets(3570): ReadAssets12-15 15:28:03.440: INFO/ReadAssets(3570): File numFiles 1412-15 15:28:03.440: INFO/ReadAssets(3570): File 0:assets/log 2.txt Size1: 138 Size2: 5512-15 15:28:03.440: INFO/ReadAssets(3570): File 1:assets/log.txt Size1: 138 Size2: 5512-15 15:28:03.440: INFO/ReadAssets(3570): File 2:res/layout/main.xml Size1: 956 Size2: 33712-15 15:28:03.440: INFO/ReadAssets(3570): File 3:AndroidManifest.xml Size1: 1348 Size2: 53112-15 15:28:03.440: INFO/ReadAssets(3570): File 4:resources.arsc Size1: 1480 Size2: 148012-15 15:28:03.440: INFO/ReadAssets(3570): File 5:res/drawable-hdpi/icon.png Size1: 3966 Size2: 396612-15 15:28:03.440: INFO/ReadAssets(3570): File 6:res/drawable-ldpi/icon.png Size1: 1537 Size2: 153712-15 15:28:03.440: INFO/ReadAssets(3570): File 7:res/drawable-mdpi/icon.png Size1: 2200 Size2: 220012-15 15:28:03.440: INFO/ReadAssets(3570): File 8:classes.dex Size1: 3468 Size2: 168012-15 15:28:03.440: INFO/ReadAssets(3570): File 9:lib/armeabi/libzip.so Size1: 217246 Size2: 4614012-15 15:28:03.440: INFO/ReadAssets(3570): File 10:lib/armeabi/libreadres.so Size1: 3820 Size2: 177912-15 15:28:03.440: INFO/ReadAssets(3570): File 11:META-INF/MANIFEST.MF Size1: 852 Size2: 44312-15 15:28:03.440: INFO/ReadAssets(3570): File 12:META-INF/CERT.SF Size1: 905 Size2: 48712-15 15:28:03.440: INFO/ReadAssets(3570): File 13:META-INF/CERT.RSA Size1: 776 Size2: 60612-15 15:28:03.440: INFO/ReadAssets(3570): : 。。。。。。。。。。。。。。。。12-15 15:28:03.440: INFO/ReadAssets(3570): 这个例子从jni读取assets内文件12-15 15:28:03.440: INFO/ReadAssets(3570): 。。。。。。。。。。。。。。。。

上面例子使用android.mk如下

LOCAL_PATH := $(call my-dir)include $(CLEAR_VARS)LOCAL_MODULE    := readresLOCAL_SRC_FILES := readres.cLOCAL_C_INCLUDES+= /opt/android-ndk-r5/platforms/android-9/arch-arm/usr/includeLOCAL_LDLIBS    += -L/opt/android-ndk-r5/platforms/android-9/arch-arm/usr/lib/ -llogLOCAL_LDLIBS    += -landroidLOCAL_LDLIBS    += -lzLOCAL_LDLIBS    += -L$(LOCAL_PATH) -lzipinclude $(BUILD_SHARED_LIBRARY)

log.txt内容如下

。。。。。。。。。。。。。。。。这个例子从jni读取assets内文件。。。。。。。。。。。。。。。。