Google App Engine上传和显示图片

实现功能：

1. 通过Web界面上传本地图片文件到GAE的Blobstore；

2. 通过GAE自动生成的URL访问图片；

3. 手动提供图片访问服务；

代码：

上传页面（hello.jsp）

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ page import="com.google.appengine.api.blobstore.BlobstoreServiceFactory" %>
<%@ page import="com.google.appengine.api.blobstore.BlobstoreService" %>

<%
    BlobstoreService blobstoreService = BlobstoreServiceFactory.getBlobstoreService();
%>

<html>
  <head>
    <link type="text/css" rel="stylesheet" href="/stylesheets/main.css" />
  </head>

  <body>

  <h1>ImageUpload</h1>
  <h2>New</h2>

  <form action="<%= blobstoreService.createUploadUrl("/upload") %>" method="post" enctype="multipart/form-data">
    <input type="file" name="myFile">
    <input type="submit" value="Submit">
  </form>

  </body>
</html>

Upload.java

package gaeimage;

import java.io.IOException;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.google.appengine.api.blobstore.BlobKey;
import com.google.appengine.api.blobstore.BlobstoreService;
import com.google.appengine.api.blobstore.BlobstoreServiceFactory;

public class Upload extends HttpServlet {
private BlobstoreService blobstoreService = BlobstoreServiceFactory.getBlobstoreService();

    public void doPost(HttpServletRequest req, HttpServletResponse res)
        throws ServletException, IOException {

        Map<String, BlobKey> blobs = blobstoreService.getUploadedBlobs(req);
        BlobKey blobKey = blobs.get("myFile");

        if (blobKey == null) {
            res.sendRedirect("/");
        } else {
            res.sendRedirect("/server?blob-key=" + blobKey.getKeyString());
        System.out.println(blobKey.getKeyString());
        }
    }
}

Server.java

package gaeimage;

import java.io.IOException;

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

import com.google.appengine.api.blobstore.BlobInfo;
import com.google.appengine.api.blobstore.BlobInfoFactory;
import com.google.appengine.api.blobstore.BlobKey;
import com.google.appengine.api.blobstore.BlobstoreService;
import com.google.appengine.api.blobstore.BlobstoreServiceFactory;
import com.google.appengine.api.images.Image;
import com.google.appengine.api.images.ImagesService;
import com.google.appengine.api.images.ImagesServiceFactory;
import com.google.appengine.api.images.Transform;

public class Server extends HttpServlet {
BlobKey blobKey;
private ImagesService imagesService = ImagesServiceFactory.getImagesService();
private BlobstoreService blobstoreService = BlobstoreServiceFactory.getBlobstoreService();

public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException {

String type=req.getParameter("type");

if (type == null)
{
blobKey = new BlobKey(req.getParameter("blob-key"));
String imageUrl = imagesService.getServingUrl(blobKey);    
System.out.println(imageUrl);
}
else if (type.equalsIgnoreCase("showImage"))
{
BlobInfo blobInfo = new BlobInfoFactory().loadBlobInfo(blobKey);
byte[] imageData = blobstoreService.fetchData(blobKey, 0, blobInfo.getSize());

res.setContentType("image/jpeg");
res.getOutputStream().write(imageData);
}
}


}

web.xml

<?xml version="1.0" encoding="UTF-8" standalone="no"?><web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="2.5" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee                http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">

  <!-- Servlets -->
  <servlet>
    <servlet-name>Upload</servlet-name>
    <servlet-class>gaeimage.Upload</servlet-class>
  </servlet>

  <servlet>
    <servlet-name>Server</servlet-name>
    <servlet-class>gaeimage.Server</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>Upload</servlet-name>
    <url-pattern>/upload</url-pattern>
  </servlet-mapping>

  <servlet-mapping>
    <servlet-name>Server</servlet-name>
    <url-pattern>/server</url-pattern>
  </servlet-mapping>

  <!-- Default page to serve -->
  <welcome-file-list>
    <welcome-file>hello.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <servlet-name>SystemServiceServlet</servlet-name>
    <servlet-class>com.google.api.server.spi.SystemServiceServlet</servlet-class>
    <init-param>
      <param-name>services</param-name>
      <param-value/>
    </init-param>
  </servlet>

  <servlet-mapping>
    <servlet-name>SystemServiceServlet</servlet-name>
    <url-pattern>/_ah/spi/*</url-pattern>
  </servlet-mapping>

</web-app>

与想象中的不同，访问存储在Blobstor中图像数据时，不能通过如下方法直接获取数据

ImagesService imagesService = ImagesServiceFactory.getImagesService();
Image image = ImagesServiceFactory.makeImageFromBlob(blobKey);
byte[] imageData = image.getImageData();

这样获取到的数据为空，非常奇怪的一个问题。

最终，我们可以通过web页面上传图像之后，通过：your_url/type=showImage 来访问上传的图像。

秒客网

Google App Engine上传和显示图片

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