在GWT中，给定blobstore键的字符串版本，如何显示来自appengine服务器的图像

Question

在GWT中，我如何显示来自appengine服务器端blobstore的图像，给定密钥的字符串版本？

我想我已经在AppEngine上以blob的形式存储了一个图像。有人能告诉我这是不是正确的吗？

try 
                            {
                                FileService fileService = FileServiceFactory.getFileService();
                                AppEngineFile file = fileService.createNewBlobFile(content_type, fileName);
                                boolean lock = true;
                                FileWriteChannel writeChannel = fileService.openWriteChannel(file, lock);
                                byte[] b1 = new byte[BUFFER_SIZE];
                                int readBytes1;
                                while ((readBytes1 = is.read(b1)) != -1) 
                                {
                                    writeChannel.write(ByteBuffer.wrap(b1, 0, readBytes1));
                                }

                                writeChannel.closeFinally();
                                item_image_blob_key = fileService.getBlobKey(file).getKeyString();
                            } 
                            catch (Exception e) 
                            {
                                System.out.println(e.getLocalizedMessage());
                                e.printStackTrace(response.getWriter());
                            }

我把钥匙送回给客户，我正在尝试呈现图像。我尝试使用：

ImagesService imagesService = ImagesServiceFactory
                .getImagesService();

        // Get the image serving URL
        String imageUrl = imagesService.getServingUrl(blobKey);

但它被否决了,所以我试着：

 ImagesService imagesService = ImagesServiceFactory.getImagesService();
              ServingUrlOptions suo = ServingUrlOptions.Builder.withBlobKey(blobKey);
              String image_url = imagesService.getServingUrl(suo);

              item.setProperty("image_url", image_url);

现在我得到一个URL,如下所示：

http://0.0.0.0:8888/_ah/img/5nXYgHwfiMmblDFldDXSew

并在客户端上创建映像,这样：

String image_url = result.get_image_url();
                    System.out.println("image url is: " + image_url);

                    Image image = new Image();
                    image.setUrl(image_url);

                    RootPanel.get("dynamicDate").add(image);

UI上只显示默认图像图标

因此，我创建了一个servlet，它访问blobstore，如下所示：

import java.io.IOException;

导入javax.servlet.http.HttpServlet；导入javax.servlet.http.HttpServletRequest；导入javax.servlet.http.HttpServletResponse；

导入com.google.appengine.api.blobstore.blobkey；导入com.google.appengine.api.blobstore.blobstoreservice；导入com.google.appengine.api.blobstore.blobstoreserviceFactory；

公共类ImageServlet扩展HttpServlet{private static final long serialVersionUID=1L；

@override public void doGet（HttpServletRequest req,HttpServletResponse res）抛出IOException{String blob_key=req.getParameter（“blob-key”）；

    if (blob_key != null) 
    {
      BlobKey blobKey = new BlobKey(blob_key);
      BlobstoreService blobstoreService = BlobstoreServiceFactory.getBlobstoreService();

      blobstoreService.serve(blobKey, res);
    } 
    else 
    {
      res.sendError(400, "One or more parameters are not set");
    }

}}

和客户端http请求：

RequestBuilder requestBuilder = new RequestBuilder(RequestBuilder.GET, "/itemmanager/image");

                    try 
                    {
                        Request request = requestBuilder.sendRequest(null, new RequestCallback() {

                        public void onError(Request request, Throwable exception) 
                        {
                           System.out.println(exception.getMessage());
                        }

                        public void onResponseReceived(Request request, Response response) 
                        {
                            System.out.println("so far so good");
                            System.out.println(response.getHeadersAsString());

                          if (200 == response.getStatusCode()) 
                          {

                          } 
                          else 
                          {
                            // Handle the error.  Can get the status text from response.getStatusText()
                          }
                        }       
                          });
                        } catch (RequestException e) {
                          // Couldn't connect to server        
                        }

我似乎在获取文本，我如何获取输入流或我可以获取图像的东西？

Answer 1

最后，经过两天的搜索，谷歌和堆栈溢出和尝试，我得到了它！

在服务器上，我获得了如下上传url：

 ImagesService imagesService = ImagesServiceFactory.getImagesService();
              ServingUrlOptions suo = ServingUrlOptions.Builder.withBlobKey(blobKey);
              String image_url = imagesService.getServingUrl(suo);

              item.setProperty("image_url", image_url);

appengine API产生了一个在本地模式下不起作用的url（我认为这与sop跨平台问题有关）

http://0.0.0.0:8888/_ah/img/mR9SOTSEizec4gZYsRnuEw

但它提供了一条线索：即字符串的/_ah/img/部分

所以我决定尝试一下，并将这个URL提供给图像“/_AH/IMG/MR9SOTSECICEC4GZYSRNUEW”，这里是客户端代码。

String imageKey = result.get_image_key();
                    System.out.println("category is: " + result.get_category() + "   image blob key is: " + imageKey);

                    String image_url = result.get_image_url();
                    System.out.println("image url is: " + image_url);

                    //This doesn't work at least locally
                    /*Image image = new Image();
                    image.setUrl(image_url);

                    RootPanel.get("dynamicDate").add(image);*/

                    Image image2 = new Image();
                    image2.setUrl("/_ah/img/" + imageKey);

                    RootPanel.get("dynamicDate").add(image2);