如何使用google app engine(java)上传和存储图像

您提供的链接 "How do I handle file uploads to my app?" 说明如何上载图像。

要承载图像,您需要使用 Datastore service 将图像与其他数据一起存储和提供服务。

下面是一个示例代码。它的意思是作为一个草图,用于说明如何让您自己的实体(如业务、用户等)拥有一个图像字段。为了简化代码,我忽略了所有错误处理和恢复。

用图像声明您的实体。您可以想象有其他字段,例如标签、位置等

@Entity
public class MyImage {
    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Long id;

    @Persistent
    private String name;

    @Persistent
    Blob image;

    public MyImage() { }
    public MyImage(String name, Blob image) {
        this.name = name; 
        this.image = image;
    }

    // JPA getters and setters and empty contructor
    // ...
    public Blob getImage()              { return image; }
    public void setImage(Blob image)    { this.image = image; }
}

然后,当您开始接受图像时(注意除了典型的文件上载失败外,还上载了同名图像的情况)。 ServletFileUpload 和 IOUtils

// Your upload handle would look like
public void doPost(HttpServletRequest req, HttpServletResponse res) {
    // Get the image representation
    ServletFileUpload upload = new ServletFileUpload();
    FileItemIterator iter = upload.getItemIterator(req);
    FileItemStream imageItem = iter.next();
    InputStream imgStream = imageItem.openStream();

    // construct our entity objects
    Blob imageBlob = new Blob(IOUtils.toByteArray(imgStream));
    MyImage myImage = new MyImage(imageItem.getName(), imageBlob);

    // persist image
    PersistenceManager pm = PMF.get().getPersistenceManager();
    pm.makePersistent(myImage);
    pm.close();

    // respond to query
    res.setContentType("text/plain");
    res.getOutputStream().write("OK!".getBytes());
}

最后,当您想为一个以其名称命名的图像提供服务时:

Blob imageFor(String name, HttpServletResponse res) {
    // find desired image
    PersistenceManager pm = PMF.get().getPersistenceManager();
    Query query = pm.newQuery("select from MyImage " +
        "where name = nameParam " +
        "parameters String nameParam");
    List<MyImage> results = (List<MyImage>)query.execute(name);
    Blob image = results.iterator().next().getImage();

    // serve the first image
    res.setContentType("image/jpeg");
    res.getOutputStream().write(image.getBytes());
}

blobstore API

BlobstoreAPI允许应用程序为数据对象提供服务,称为 斑点 斑点键 ,以后您可以使用它来提供blob。应用程序可以响应用户请求提供完整的blob值,也可以使用流文件(如接口)直接读取该值。。。

import com.google.appengine.api.files.FileService;
import com.google.appengine.api.files.AppEngineFile;
import com.google.appengine.api.files.FileWriteChannel;
import com.google.appengine.api.blobstore.BlobKey;
import com.google.appengine.api.images.ImagesServiceFactory;
import com.google.appengine.api.images.ServingUrlOptions;
...


// your data in byte[] format
byte[] data = image.getData();
/**
 *  MIME Type for
 *  JPG use "image/jpeg" for PNG use "image/png"
 *  PDF use "application/pdf"
 *  see more: https://en.wikipedia.org/wiki/Internet_media_type
 */
String mimeType = "image/jpeg";

// save data to Google App Engine Blobstore 
FileService fileService = FileServiceFactory.getFileService();
AppEngineFile file = fileService.createNewBlobFile(mimeType); 
FileWriteChannel writeChannel = fileService.openWriteChannel(file, true);
writeChannel.write(java.nio.ByteBuffer.wrap(data));
writeChannel.closeFinally();

// your blobKey to your data in Google App Engine BlobStore
BlobKey blobKey = fileService.getBlobKey(file);

// THANKS TO BLOBKEY YOU CAN GET FOR EXAMPLE SERVING URL FOR IMAGES

// Get the image serving URL (in https:// format)
String imageUrl =
  ImagesServiceFactory.getImagesService().getServingUrl(
    ServingUrlOptions.Builder.withBlobKey(blobKey
          ).secureUrl(true));