Google App Engine上传和显示图片

来源：互联网发布：plc的编程语言有哪些编辑：程序博客网时间：2024/05/10 19:05

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。