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java - 如何从 JSP 文件中删除实体(带有 Google App Engine 的 Java)

转载 作者：行者123 更新时间：2023-11-30 09:33:13 24 4
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我有一个 jsp 文件显示数据存储中的一些记录，我想在每个条目旁边有一个删除按钮，以便将其从数据库中删除。

所以，我知道 Servelet 将执行实际的删除操作，但我不确定在 jsp 中使用删除按钮放置什么，以便我的 Servlet 知道要在数据库中查找哪个实体(项目)。

有更好的方法吗？

这是我的jsp。在我有删除按钮的底部向下看:

    <%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ page import="java.util.List" %>
<%@ 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="com.google.appengine.api.datastore.DatastoreServiceFactory" %>
<%@ page import="com.google.appengine.api.datastore.DatastoreService" %>
<%@ page import="com.google.appengine.api.datastore.Query" %>
<%@ page import="com.google.appengine.api.datastore.Entity" %>
<%@ page import="com.google.appengine.api.datastore.FetchOptions" %>
<%@ page import="com.google.appengine.api.datastore.Key" %>
<%@ page import="com.google.appengine.api.datastore.KeyFactory" %>
<%@ taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions" %>

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

  <body>

<%
    String podlistName = request.getParameter("podlistName");
    if (podlistName == null) {
        podlistName = "default";
    }
    pageContext.setAttribute("podlistName", podlistName);
    UserService userService = UserServiceFactory.getUserService();
    User user = userService.getCurrentUser();
    if (user != null) {
      pageContext.setAttribute("user", user);

%>
<p>Hello, ${fn:escapeXml(user.nickname)}! (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 podcasts you post.</p>
<%
    }
%>

<%
    DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
    Key podlistKey = KeyFactory.createKey("Podlist", podlistName);
    // Run an ancestor query to ensure we see the most up-to-date
    // view of the Greetings belonging to the selected Podlist.
    Query query = new Query("Podcast", podlistKey).addSort("date", Query.SortDirection.DESCENDING);
    List<Entity> podcasts = datastore.prepare(query).asList(FetchOptions.Builder.withLimit(5));
    if (podcasts.isEmpty()) {
        %>
        <p>Podlist '${fn:escapeXml(podlistName)}' has no items.</p>
        <%
    } else {
        %>
        <p>Items in Podlist '${fn:escapeXml(podlistName)}'.</p>
        <%
        for (Entity podcast : podcasts) {
            pageContext.setAttribute("podcast_url",
                                     podcast.getProperty("podcast_url"));
            if (podcast.getProperty("user") == null) {
                %>
                <p>An anonymous person wrote:</p>
                <%
            } else {
                pageContext.setAttribute("podcast_user",
                                         podcast.getProperty("user"));
                %>
                <p><b>${fn:escapeXml(podcast_user.nickname)}</b> wrote:</p>
                <%
            }
            %>
            <blockquote>${fn:escapeXml(podcast_url)}</blockquote>
            <form action="/delete" method="post">
              <div><input type="submit" value="Delete Podcast" /></div>
              <input type="hidden" name="podlistName" value="${fn:escapeXml(podlistName)}"/>
              <!-- not sure what to put here to give a reference to this entity-->
              <input type="hidden" name="podcast_id" value="$??"/>
            </form>
            <%
        }
    }
%>

    <form action="/add" method="post">
      <div><textarea name="podcast_url" rows="3" cols="60"></textarea></div>
      <div><input type="submit" value="Post Podcast" /></div>
      <input type="hidden" name="podlistName" value="${fn:escapeXml(podlistName)}"/>
    </form>

  </body>
</html>

这是我的 Servlet:

package com.aol.sharepodder;

import java.io.IOException;
import java.util.Date;
import java.util.UUID;
import java.util.logging.Logger;

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

import com.google.appengine.api.datastore.DatastoreService;
import com.google.appengine.api.datastore.DatastoreServiceFactory;
import com.google.appengine.api.datastore.Entity;
import com.google.appengine.api.datastore.Key;
import com.google.appengine.api.datastore.KeyFactory;
import com.google.appengine.api.users.User;
import com.google.appengine.api.users.UserService;
import com.google.appengine.api.users.UserServiceFactory;

public class AddPodcastServlet extends HttpServlet {
    private static final Logger log = Logger.getLogger(AddPodcastServlet.class.getName());

    public void doPost(HttpServletRequest req, HttpServletResponse resp)
                throws IOException {
        UserService userService = UserServiceFactory.getUserService();
        User user = userService.getCurrentUser();

        String podlistName = req.getParameter("podlistName");
        Key podlistKey = KeyFactory.createKey("Podlist", podlistName);
        String podcast_url = req.getParameter("podcast_url");
        Date date = new Date();
        Entity podcast = new Entity("Podcast", podlistKey);
        podcast.setProperty("user", user);
        podcast.setProperty("date", date);
        podcast.setProperty("podcast_url", podcast_url);

        DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
        datastore.put(podcast);

        resp.sendRedirect("/podlist.jsp?podlistName=" + podlistName);
    }
}

谢谢!!

最佳答案

您似乎已经在使用“podcast_id”——那么为什么不在请求中将其传递给 /delete 处理程序呢？

podcast.getProperty("podcast_id")

我们似乎很难告诉您您需要传递什么，因为它是您的应用程序 - 但您可能想要传递一个唯一引用实体的参数(无论是“键”、“podcast_id”、 ETC)。 GAE 中的每个实体都有一个唯一的 key 。

关于java - 如何从 JSP 文件中删除实体(带有 Google App Engine 的 Java)，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/12322108/

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