2.PMF.java用來跟App Engine datastore溝通
import javax.jdo.JDOHelper;
import javax.jdo.PersistenceManagerFactory;
public final class PMF {
private static final PersistenceManagerFactory pmfInstance =
JDOHelper.getPersistenceManagerFactory("transactions-optional");
private PMF() {}
public static PersistenceManagerFactory get() {
return pmfInstance;
}
}
3.利用JDO Class自訂資料欄位
import java.util.Date;
import javax.jdo.annotations.IdGeneratorStrategy;
import javax.jdo.annotations.IdentityType;
import javax.jdo.annotations.PersistenceCapable;
import javax.jdo.annotations.Persistent;
import javax.jdo.annotations.PrimaryKey;
import com.google.appengine.api.users.User;
@PersistenceCapable(identityType = IdentityType.APPLICATION)
public class Greeting {
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
private Long id;
@Persistent
private User author;
@Persistent
private String content;
@Persistent
private Date date;
public Greeting(User author, String content, Date date) {
this.author = author;
this.content = content;
this.date = date;
}
public Long getId() {
return id;
}
public User getAuthor() {
return author;
}
public String getContent() {
return content;
}
public Date getDate() {
return date;
}
public void setAuthor(User author) {
this.author = author;
}
public void setContent(String content) {
this.content = content;
}
public void setDate(Date date) {
this.date = date;
}
}
4.用servlet新增一筆紀錄
package guestbook;
import java.io.IOException;
import java.util.Date;
import java.util.logging.Logger;
import javax.jdo.PersistenceManager;
import javax.servlet.http.*;
import com.google.appengine.api.users.User;
import com.google.appengine.api.users.UserService;
import com.google.appengine.api.users.UserServiceFactory;
import guestbook.Greeting;
import guestbook.PMF;
public class SignGuestbookServlet extends HttpServlet {
private static final Logger log = Logger.getLogger(SignGuestbookServlet.class.getName());
public void doPost(HttpServletRequest req, HttpServletResponse resp)
throws IOException {
UserService userService = UserServiceFactory.getUserService();
User user = userService.getCurrentUser();//取得登入gmail的用戶名稱
String content = req.getParameter("content");//要存入的字串
Date date = new Date();//產生目前日期時間
Greeting greeting = new Greeting(user, content, date);//將資料存入JDO物件
PersistenceManager pm = PMF.get().getPersistenceManager();//建立一個新的實例PersistenceManager
try {
pm.makePersistent(greeting);//JDO物件的資料寫入App Engine datastore
} finally {
pm.close();
}
resp.sendRedirect("/guestbook.jsp");
}
}
5.用JSP讀取資料
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ page import="java.util.List" %>
<%@ page import="javax.jdo.PersistenceManager" %>
<%@ page import="com.google.appengine.api.users.User" %>
<%@ page import="com.google.appengine.api.users.UserService" %>
<%@ page import="com.google.appengine.api.users.UserServiceFactory" %>
<%@ page import="guestbook.Greeting" %>
<%@ page import="guestbook.PMF" %>
<html>
<head>
<link type="text/css" rel="stylesheet" href="/stylesheets/main.css" />
</head>
<body>
<%
UserService userService = UserServiceFactory.getUserService();
User user = userService.getCurrentUser();
if (user != null) {
%>
<p>Hello, <%= user.getNickname() %>! (You can
<a href="<%= userService.createLogoutURL(request.getRequestURI()) %>">sign out</a>.)</p>
<%
} else {
%>
<p>Hello!
<a href="<%= userService.createLoginURL(request.getRequestURI()) %>">Sign in</a>
to include your name with greetings you post.</p>
<%
}
%>
<%
PersistenceManager pm = PMF.get().getPersistenceManager();
String query = "select from " + Greeting.class.getName() + " order by date desc range 0,5";
List<Greeting> greetings = (List<Greeting>) pm.newQuery(query).execute();
if (greetings.isEmpty()) {
%>
<p>The guestbook has no messages.</p>
<%
} else {
for (Greeting g : greetings) {
if (g.getAuthor() == null) {
%>
<p>An anonymous person wrote:</p>
<%
} else {
%>
<p><b><%= g.getAuthor().getNickname() %></b> wrote:</p>
<%
}
%>
<blockquote><%= g.getContent() %></blockquote>
<%
}
}
pm.close();
%>
<form action="/sign" method="post">
<div><textarea name="content" rows="3" cols="60"></textarea></div>
<div><input type="submit" value="Post Greeting" /></div>
</form>
</body>
</html>
資料來源http://code.google.com/intl/en/appengine/docs/java/gettingstarted/usingdatastore.html
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