android常見問題之jni讀取assets資源文件

assets目錄底下的文件會被打包到一個apk文件裏，這些資源在安裝時他們並沒被解壓,使用時是直接從apk中讀取的。這裏介紹下怎麼在jni內使用 ndk自帶api的接口函數讀取assets資源文件，和libzip庫函數的使用，可以用來讀創建修改壓縮文檔，這裏也是以讀取apk安裝包內的資源文 件爲例。

1 用ndk自帶的接口函數讀apk包

從2.3開始提供這些接口函數，具體看頭文件assert.h android/asset_manager.h android/asset_manager_jni.h，可以參考ndk自帶例子中samples/native-audio/ jni/native-audio-jni.c。

/**************************************
* Function Name  : java_com_fontlose_ReadAssets_readFromAssets
* Description    : void  readFromAssets(AssetManager ass,String filename);
* Input          : AssetManager對象 filename資源名
* 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 ;
   }

    /*獲取文件名並打開*/
   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 ;
   }
   /*獲取文件大小*/
   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);
    /*關閉文件*/
   AAsset_close(asset);
}

在應用程序內使用定義和使用如下

public native void  readFromAssets(AssetManager ass,String filename);

readFromAssets(getAssets(),"log.txt");

logcat測試結果

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): 這個例子從jni讀取assets內文件
12-15 15:27:33.290: INFO/ReadAssets(3570): 。。。。。。。。。。。。。。。。
2 使用libzip庫讀apk包
     libzip 使用 C 庫來 讀創建修改壓縮文檔，關於libzip在andorid的移植可以參考老外做的android-ndk-assets.zip這個工程，已在NDK下可以編譯了，修改下編譯生成libzip.so，利用libzip.so和zip.h建立工程，使用libzip還可以讀取apk包內其他壓縮文件如AndroidManifest.xml佈局xml等。

/*************************************
* Function Name  : java_com_fontlose_ReadAssets_readFromAssetsLibzip
* Description    : void readFromAssetsLibzip(String apkpath,String filename);
* Input          : apkpath路徑 filename 資源名
* 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);
}

在應用程序內使用定義和使用如下

public native void  readFromAssetsLibzip(String apkpath,String filename);

readFromAssetsLibzip(getPackageResourcePath(),"assets/log.txt");

logcat測試結果

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): 這個例子從jni讀取assets內文件
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)

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