android常见问题之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    : 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): ReadAssets

12-15 15:27:33.290: INFO/ReadAssets(3570): file size : 138

12-15 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。

/*************************************
* Function Name  : java_com_fontlose_ReadAssets_readFromAssetsLibzip
* Description    : void readFromAssetsLibzip(String apkpath,String filename);
* Input          : apkpath路径 filename 资源名
* Output         : None
* Return         : None
**************************************/
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): ReadAssets

12-15 15:28:03.440: INFO/ReadAssets(3570): File numFiles 14

12-15 15:28:03.440: INFO/ReadAssets(3570): File 0:assets/log 2.txt Size1: 138 Size2: 55

12-15 15:28:03.440: INFO/ReadAssets(3570): File 1:assets/log.txt Size1: 138 Size2: 55

12-15 15:28:03.440: INFO/ReadAssets(3570): File 2:res/layout/main.xml Size1: 956 Size2: 337

12-15 15:28:03.440: INFO/ReadAssets(3570): File 3:AndroidManifest.xml Size1: 1348 Size2: 531

12-15 15:28:03.440: INFO/ReadAssets(3570): File 4:resources.arsc Size1: 1480 Size2: 1480

12-15 15:28:03.440: INFO/ReadAssets(3570): File 5:res/drawable-hdpi/icon.png Size1: 3966 Size2: 3966

12-15 15:28:03.440: INFO/ReadAssets(3570): File 6:res/drawable-ldpi/icon.png Size1: 1537 Size2: 1537

12-15 15:28:03.440: INFO/ReadAssets(3570): File 7:res/drawable-mdpi/icon.png Size1: 2200 Size2: 2200

12-15 15:28:03.440: INFO/ReadAssets(3570): File 8:classes.dex Size1: 3468 Size2: 1680

12-15 15:28:03.440: INFO/ReadAssets(3570): File 9:lib/armeabi/libzip.so Size1: 217246 Size2: 46140

12-15 15:28:03.440: INFO/ReadAssets(3570): File 10:lib/armeabi/libreadres.so Size1: 3820 Size2: 1779

12-15 15:28:03.440: INFO/ReadAssets(3570): File 11:META-INF/MANIFEST.MF Size1: 852 Size2: 443

12-15 15:28:03.440: INFO/ReadAssets(3570): File 12:META-INF/CERT.SF Size1: 905 Size2: 487

12-15 15:28:03.440: INFO/ReadAssets(3570): File 13:META-INF/CERT.RSA Size1: 776 Size2: 606

12-15 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 := readres

LOCAL_SRC_FILES := readres.c

LOCAL_C_INCLUDES+= /opt/android-ndk-r5/platforms/android-9/arch-arm/usr/include

LOCAL_LDLIBS += -L/opt/android-ndk-r5/platforms/android-9/arch-arm/usr/lib/ -llog

LOCAL_LDLIBS += -landroid

LOCAL_LDLIBS += -lz

LOCAL_LDLIBS += -L$(LOCAL_PATH) -lzip

include $(BUILD_SHARED_LIBRARY)

转自：http://www.rosoo.net/a/201112/15459.html