[英]set-attribute and Get-attribute servlet to jsp
在这里我提出了一个问题，比如通过set属性在servlet和jsp之间传递值，get属性我已经在servlet中创建了servlet页面和设置值，现在我怎样才能通过get属性迭代jsp中的所有值。新手可能会有一个指南纠正我的代码，向大家学习是有用的
它的工作正常，但我点击更新和删除链接它显示这样的错误
Controllertest.java：
package Controller;
import java.io.IOException;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import dao.UserDao;
import dbBean.UseBean;
public class ControllerTest extends HttpServlet
{
private static final long serialVersionUID = 1L;
private static String INSERT_OR_EDIT = "/user.jsp";
private static String LIST_USER = "/listUser.jsp";
private UserDao dao;
public ControllerTest()
{
super();
dao = new UserDao();
}
protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException
{
String forward = "";
String action = request.getParameter("action");
if (action.equalsIgnoreCase("delete"))
{
int userId = Integer.parseInt(request.getParameter("userId"));
dao.deleteUser(userId);
forward = LIST_USER;
request.setAttribute("users", dao.getAllUsers());
}
else if (action.equalsIgnoreCase("edit"))
{
forward = INSERT_OR_EDIT;
int userId = Integer.parseInt(request.getParameter("userId"));
UseBean bean = dao.getUserById(userId);
request.setAttribute("user", bean);
}
else if (action.equalsIgnoreCase("listUser"))
{
forward = LIST_USER;
request.setAttribute("users", dao.getAllUsers());
}
else
{
forward = INSERT_OR_EDIT;
}
RequestDispatcher view = request.getRequestDispatcher(forward);
view.forward(request, response);
}
protected void doPost(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException
{
UseBean bean = new UseBean();
bean.setName(request.getParameter("Name"));
bean.setPassword(request.getParameter("password"));
bean.setPhoneo(request.getParameter("Phoneo"));
bean.setEmailID(request.getParameter("Emailid"));
String userid = request.getParameter("ID");
if (userid == null || userid.isEmpty())
{
dao.addUser(bean);
}
else
{
bean.setID(Integer.parseInt(userid));
dao.updateUser(bean);
}
RequestDispatcher view = request.getRequestDispatcher(LIST_USER);
request.setAttribute("users", dao.getAllUsers());
view.forward(request, response);
}
}
user.jsp
<form method="POST" action='ControllerTest' name="frmAddUser">
<jsp:useBean id="users" class="java.util.ArrayList" scope="request" />
<% for(int i = 0; i < users.size(); i+=1)
{
UseBean user = (UseBean)users.get(i);
%>
id:<input type="text" name="ID" value="<%=user.getID() %>"><br/>
Name:<input type="text" name="Name" value="<%= user.getName() %>"><br/>
Password:<input type="text" name="password" value="<%= user.getPassword() %>"><br/>
phoneno:<input type="text" name="Phoneo" value="<%= user.getPhoneo() %>"><br/>
Emailid:<input type="text" name="Emailid" value="<%= user.getEmailID() %>"> <br/>
<%} %>
<input type="submit" value="Submit" />
</form>
listuser.jsp
<%@ page language="java" contentType="text/html; charset=EUC-KR"
pageEncoding="EUC-KR"%>
<%@page import="java.util.*,Controller.*,dbBean.*,Dbconnect.*"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=EUC-KR">
<title>Show All Users</title>
</head>
<body>
<table border=1>
<thead>
<tr>
<th>Id</th>
<th>Name</th>
<th>password</th>
<th>phoneno</th>
<th>emailid</th>
<th colspan=2>Action</th>
</tr>
</thead>
<tbody>
<jsp:useBean id="users" class="java.util.ArrayList" scope="request" />
<% for(int i = 0; i < users.size(); i+=1)
{
UseBean user = (UseBean)users.get(i);
%>
<tr>
<td><%= user.getID() %></td>
<td><%= user.getName() %></td>
<td><%= user.getPassword() %></td>
<td><%= user.getEmailID() %></td>
<td><%= user.getPhoneo() %></td>
<td><a href="ControllerTest?action=edit&userId=<%= user.getID() %>" >Update</a></td>
<td><a href="ControllerTest?action=delete&userId=<%= user.getID() %>">Delete</a></td>
</tr>
<% } %>
</tbody>
</table>
<p>
<a href="ControllerTest?action=insert">Add User</a>
</p>
</body>
</html>
根据评论更新。
User.jsp
<form method="POST" action='ControllerTest' name="frmAddUser">
<jsp:useBean id="user" class="dbBean.UseBean" scope="request" />
id:<input type="text" name="ID" value="<%=user.getID() %>"><br/>
Name:<input type="text" name="Name" value="<%= user.getName() %>"><br/>
Password:<input type="text" name="password" value="<%= user.getPassword() %>"><br/>
phoneno:<input type="text" name="Phoneo" value="<%= user.getPhoneo() %>"><br/>
Emailid:<input type="text" name="Emailid" value="<%= user.getEmailID() %>"> <br/>
<input type="submit" value="Submit" />
</form>
首先，您应该尝试避免使用scriptlet。 由于这只是为了学习目的，您可以遵循此代码。
你的arraylist打印null的原因是在servlet的doPost方法中你将属性名称设置为“users”，而在jsp中你试图访问“user”。 （注意单数复数差异）。 你应该纠正这一点。 如果它仍然为null检查您的dao。 在servlet类中设置attruibute时尝试打印值。
另请注意bean名称..它的UseBean。 我认为它应该是UserBean;）
<%@ page language="java" contentType="text/html; charset=EUC-KR"
pageEncoding="EUC-KR"%>
<%@page import="java.util.*,Controller.*,dbBean.*,Dbconnect.*"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=EUC-KR">
<title>Show All Users</title>
</head>
<body>
<table border=1>
<thead>
<tr>
<th>Id</th>
<th>Name</th>
<th>password</th>
<th>phoneno</th>
<th>emailid</th>
<th colspan=2>Action</th>
</tr>
</thead>
<tbody>
<jsp:useBean id="users" type="java.util.ArrayList" scope="request" />
<% for(int i = 0; i < users.size(); i+=1) {
UseBean user = (UseBean)users.get(i);
%>
<tr>
<td><%= user.getID() %></td>
<td><%= user.getName() %></td>
<td><%= user.getPassword() %></td>
<td><%= user.getEmailID() %></td>
<td><%= user.getPhoneo() %></td>
<td><a href="ControllerTest?action=edit&userId=<%= user.getID() %>" >Update</a></td>
<td><a href="ControllerTest?action=delete&userId=<%= user.getID() %>">Delete</a></td>
</tr>
<% } %>
</tbody>
</table>
<p>
<a href="ControllerTest?action=insert">Add User</a>
</p>
</body>
</html>
Jstl解决方案
使用jstl。 这是最好的选择。 您可以在线获取大量文档。 对于你的情况，它应该是如下所示。 请注意标记lib的包含
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
完成后，您可以使用foreach迭代列表，如下所示。
<%@ page language="java" contentType="text/html; charset=EUC-KR"
pageEncoding="EUC-KR"%>
<%@page import="java.util.*,Controller.*,dbBean.*,Dbconnect.*"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=EUC-KR">
<title>Show All Users</title>
</head>
<body>
<table border=1>
<thead>
<tr>
<th>Id</th>
<th>Name</th>
<th>password</th>
<th>phoneno</th>
<th>emailid</th>
<th colspan=2>Action</th>
</tr>
</thead>
<tbody>
<c:forEach items="${user}" var="element">
<tr>
<td>${element.id}</td>
<td>${element.name}</td>
<td>${element.password}</td>
<td>${element.phoneno}</td>
<td>${element.emailid}</td>
<td><a href="ControllerTest?action=edit&userId=">Update</a></td>
<td><a href="ControllerTest?action=delete&userId=">Delete</a></td>
</tr>
</c:forEach>
</tbody>
</table>
<p>
<a href="ControllerTest?action=insert">Add User</a>
</p>
</body>
</html>
我在这里假设arraylist包含User对象。 您可以将arraylist作为常规Java代码进行迭代，并将其嵌入HTML标记中。
<tbody>
<%
List<User> al1 = (List) request.getAttribute("user");
System.out.println(al1); // prints null
for(User user : al1) {
%>
<tr>
<td><%= user.getName() %></td>
<td><%= user.getAge() %></td>
<td><%= user.getRole() %></td>
<td><%= user.getDescription() %></td>
<td><a href="ControllerTest?action=edit&userId=">Update</a></td>
<td><a href="ControllerTest?action=delete&userId=">Delete</a></td>
</tr>
<% } %>
</tbody>
你也可以看到这个答案 。
无法获取由Servlet设置并转发到JSP的属性（在请求范围内）
[英]Cannot get attribute (in request scope) set by Servlet and forwarded to JSP
无法获取Java Servlet的请求中设置的JSP中的属性？
[英]Not getting the attribute in jsp which is set in request in java servlet?
声明:本站的技术帖子网页，遵循CC BY-SA 4.0协议，如果您需要转载，请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.