移动后端起始套件 - 上传到AppEngine Blobstore

Question

如何使用Mobile Backend Starter或Google Cloud Endpoints将Android中的文件上传到Google App Engine Blobstore？

- JR Galia

Answer 1

分享我使用移动后端入门的经验。

要获取上传和下载URL，您需要将这两个方法添加到CloudBackend.java类中，以使URL从Activity中可访问：

public String getUploadBlobURL(String bucketName, String path, String accessMode) {

        String url = null;
        try {
            url = getMBSEndpoint().blobEndpoint()
                    .getUploadUrl(bucketName, path, accessMode).execute()
                    .getShortLivedUrl();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return url;
    }

public String getDownloadBlobURL(String bucketName, String path) {

        String url = null;
        try {
            url = getMBSEndpoint().blobEndpoint()
                    .getDownloadUrl(bucketName, path).execute()
                    .getShortLivedUrl();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return url;
    }

接下来，您可以使用标准客户端库的URL将字节流式传输到Google Cloud Storage。

以下是如何使用它们的示例。

要将文件上传到Google Cloud Storage，您可以使用类似于以下内容的代码：

活动

File fileUp = new File(Environment.getExternalStorageDirectory(), fileName);
        new AsyncBlobUploader(this, mProcessingFragment.getCloudBackend()).execute(fileUp);

异步任务

public class AsyncBlobUploader extends AsyncTask<File, Void, String> {
    private Context context;
    private ProgressDialog pd;
    private CloudBackend cb;

    public AsyncBlobUploader(Context context, CloudBackend cb) {
        this.context = context;
        this.cb = cb;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pd = ProgressDialog.show(context, null,
                "Loading... Please wait...");
        pd.setProgressStyle(ProgressDialog.STYLE_SPINNER);
        pd.setIndeterminate(true);
        pd.setCancelable(true);
        pd.show();
    }

    protected String doInBackground(File... files) {
        File file = files[0];
        String uploadUrl = cb.getUploadBlobURL(bucketName, file.getName(),"PUBLIC_READ_FOR_APP_USERS");
        String url = uploadUrl.split("&Signature")[0]; // url without Signature

        HttpClient httpclient = new DefaultHttpClient();
        HttpPost httppost = new HttpPost(url);

        FileBody filebody = new FileBody(file,ContentType.create(getMimeType(file
                .toString())), file.getName());

        MultipartEntityBuilder multipartEntity = MultipartEntityBuilder.create();        
        multipartEntity.setMode(HttpMultipartMode.BROWSER_COMPATIBLE);
        multipartEntity.addPart("file", filebody);
        httppost.setEntity(multipartEntity.build());
        System.out.println( "executing request " + httppost.getRequestLine( ) );
        try {
            HttpResponse response = httpclient.execute( httppost );
            Log.i("response", response.getStatusLine().toString());
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        httpclient.getConnectionManager( ).shutdown( );

        return (String) uploadUrl;
    }

    protected void onPostExecute(String result) {

        pd.dismiss();
        Log.d("BlobUrl", result);

    }

    public static String getMimeType(String url) {
        String type = null;
        String extension = MimeTypeMap.getFileExtensionFromUrl(url);
        if (extension != null) {
            MimeTypeMap mime = MimeTypeMap.getSingleton();
            type = mime.getMimeTypeFromExtension(extension);
        }
        return type;
    }
}

MultipartEntityBuilder 类不包含在 Android 标准库中，所以您需要下载 httpclient 并将其包含到您的项目中。

请注意这行代码：String url = uploadUrl.split("&Signature")[0];，我在此截掉了 URL 签名。（带有 URL 签名会导致出现 503 Internal Server Error 错误，但没有签名时一切正常，我不知道为什么会这样。）

以下代码片段可用于下载：

Activity

File fileDown = new File(Environment.getExternalStorageDirectory(),
                fileName); //file to create
        new AsyncBlobDownloader(imageView, mProcessingFragment.getCloudBackend())
            .execute(fileDown);

异步任务

public class AsyncBlobDownloader extends AsyncTask<File, Integer, File> {
    private ImageView imageView;
    private ProgressDialog pd;
    private CloudBackend cb;

    public AsyncBlobDownloader(ImageView imageView, CloudBackend cb) {
        this.imageView = imageView;
        this.cb = cb;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pd = ProgressDialog.show(imageView.getContext(), null,
                "Loading... Please wait...");
        pd.setProgressStyle(ProgressDialog.STYLE_SPINNER);
        pd.setCancelable(true);
        pd.show();
    }

    protected File doInBackground(File... files) {
        File file = files[0];
        String downloadUrl = cb.getDownloadBlobURL(bucketName,
                file.getName());
        InputStream input = null;
        OutputStream output = null;
        HttpURLConnection connection = null;
        try {
            URL url = new URL(downloadUrl);
            connection = (HttpURLConnection) url.openConnection();
            connection.connect();
            if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
                Log.i("Response",
                        "Server returned HTTP " + connection.getResponseCode()
                                + " " + connection.getResponseMessage());
            }
            int fileLength = connection.getContentLength();

            input = connection.getInputStream();
            output = new FileOutputStream(file);

            byte data[] = new byte[4096];

            int count;
            while ((count = input.read(data)) != -1) {
                if (isCancelled()) {
                    input.close();
                    return null;
                }
                output.write(data, 0, count);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (output != null)
                    output.close();
                if (input != null)
                    input.close();
            } catch (IOException ignored) {
            }

            if (connection != null)
                connection.disconnect();
        }    
        return file;
    }

    protected void onPostExecute(File result) {    
        pd.dismiss();
        imageView.setImageURI(Uri.fromFile(result));   
    }   
}

注意：使用 Google Cloud Storage 需要开启计费功能。此外，您还需要在 GCS 中创建存储桶。

- Juniper