file：// android_assets /和http://someurl.com/之間的區別？

Question

我有一個android應用，可從網絡上的JSON文件加載圖像。 JSON文件中包含一個URL，其中包含圖像上的位置。 通常，該應用會讀取JSON文件以從網絡廣告下載圖像。 但是現在我想從我的資產文件夾中下載文件，並讀取我的資產目錄中的JSON文件（我正在使用file：// android_assets）。

我的第一個問題是，為什么不能從資產文件夾中讀取json文件？

我的JSON文件，解決我的第一個問題並不是真正需要，但我只發布了它：

舊的JSON：

[
{
    "id": "1",
    "title": "Blue Calmness",
    "thumburl": "http://someurl.com/1.jpg",
    "previewurl": "http://someurl.com/1.jpg",
    "url": "http://someurl.com/1.jpg",
    "text": "Give your background a special message! An inspirational image, the texture and its calm blue color are stimulating and representing the silent word of the see. For a positive look at the world."
}
]

新的JSON：

[
{
    "id": "1",
    "title": "Blue Calmness",
    "thumburl": "file:///android_assets/1.jpg",
    "previewurl": "file:///android_assets/1.jpg",
    "url": "file:///android_assets/1.jpg",
    "text": "Give your background a special message! An inspirational image, the texture and its calm blue color are stimulating and representing the silent word of the see. For a positive look at the world."
}
]

但是我收到錯誤消息：

   04-29 21:52:42.169: E/AndroidRuntime(23408): FATAL EXCEPTION: main
   04-29 21:52:42.169: E/AndroidRuntime(23408): java.lang.RuntimeException: java.lang.IllegalArgumentException: Host name may not be null
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at app.wallpaper.main.ScroidWallpaperGallery$FillGalleryTask.handleUncaughtException(ScroidWallpaperGallery.java:415)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at app.wallpaper.util.threading.LongTimeRunningOperation$InnerAsyncTask.onPostExecute(LongTimeRunningOperation.java:87)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at android.os.AsyncTask.finish(AsyncTask.java:631)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at android.os.AsyncTask.access              $600(AsyncTask.java:177)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at android.os.Handler.dispatchMessage(Handler.java:99)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at android.os.Looper.loop(Looper.java:137)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at android.app.ActivityThread.main(ActivityThread.java:5041)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at java.lang.reflect.Method.invokeNative(Native Method)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at java.lang.reflect.Method.invoke(Method.java:511)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at dalvik.system.NativeStart.main(Native Method)
   04-29 21:52:42.169: E/AndroidRuntime(23408): Caused by: java.lang.IllegalArgumentException: Host name may not be null
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at org.apache.http.HttpHost.<init>(HttpHost.java:83)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at org.apache.http.impl.client.AbstractHttpClient.determineTarget(AbstractHttpClient.java:497)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:626)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:616)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at app.wallpaper.main.dao.wallpapers.WallpaperDAO.download(WallpaperDAO.java:105)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at app.wallpaper.main.dao.wallpapers.WallpaperDAO.getAvailableWallpapers(WallpaperDAO.java:61)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at app.wallpaper.main.core.wallpapers.WallpaperManager.loadAvailableWallpapers(WallpaperManager.java:92)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at app.wallpaper.main.ScroidWallpaperGallery$FillGalleryTask.onRun(ScroidWallpaperGallery.java:425)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at app.wallpaper.main.ScroidWallpaperGallery$FillGalleryTask.onRun(ScroidWallpaperGallery.java:1)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at app.wallpaper.util.threading.LongTimeRunningOperation$InnerAsyncTask.doInBackground(LongTimeRunningOperation.java:73)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at app.wallpaper.util.threading.LongTimeRunningOperation$InnerAsyncTask.doInBackground(LongTimeRunningOperation.java:1)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at android.os.AsyncTask$2.call(AsyncTask.java:287)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at java.util.concurrent.FutureTask.run(FutureTask.java:234)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
   04-29 21:52:42.169: E/AndroidRuntime(23408):     at java.lang.Thread.run(Thread.java:856)

我從服務器下載json的代碼：

    @Inject
WallpaperDAO(IWallpaperParser wallpaperParser) {
    super();

    this.wallpaperParser = wallpaperParser;
}


/* (non-Javadoc)
 * @see app.wallpaper.main.dao.wallpapers.IWallpaperDAO#getAvailableWallpapers(android.content.Context)
 */
public Wallpaper[] getAvailableWallpapers(Context context) throws WallpaperListReceivingException {     
    try {
        String data = this.download(URI.create(context.getString(R.string.galleryUrl)), 
                                    new TextFileHttpResponseHandler(),
                                    MAX_DOWNLOAD_RETRIES);

        List<Wallpaper> wallpapers = this.wallpaperParser.parse(data);

        return wallpapers.toArray(new Wallpaper[wallpapers.size()]);
    }
    catch (IllegalStateException ex) {
        throw new WallpaperListReceivingException(context.getString(R.string.receivingException), ex);
    }
    catch (IOException ex) {
        throw new WallpaperListReceivingException(context.getString(R.string.receivingException), ex);
    }
    catch (ParseException ex) {
        throw new WallpaperListReceivingException(context.getString(R.string.parseExceptionText), ex);
    }
}

其中galleryUrl是file：//android_assets/myfile.json

現在我想知道，為什么Android無法從我的Assets文件夾加載我的JSON文件，而卻可以從我的Web服務器加載它。 並且有辦法解決這個問題。

任何幫助表示贊賞！

Answer 1

file：///代表一個不同於HTTP URI的URI，它指向資產目錄中包含的數據。 您的下載方法顯然是為HTTP URL設計的。

為了從資產目錄中加載數據，您可以使用AssetManager ，尤其可以使用open方法。

例如：

AssetManager assetMgr = this.getAssets()
InputStream is = assetMgr.open("1.jpg");