web实现登录错误后跳转界面

1.要先写好一个login.html，代码如下：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<h2>用户登录</h2>
<form action="login" method="get">
    <p>账号：<input type="text" name="name"></p>
    <p>密码：<input type="text" name="passWord"> </p>
    <input type="submit" value="提交">
</form>
</body>
</html>

2.创建一个login的servlet

package net.zixue.servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet(name = "LoginServlet",urlPatterns = "/login")
public class LoginServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        String userName="jiangyi";
        String userPass="123";
        String name = request.getParameter("name");
        String passWord = request.getParameter("passWord");
        if(!name.equals(userName))
        {
            //用户名错误
            request.setAttribute("errorMessage","用户名错误");
            request.getRequestDispatcher("/loginError.jsp").forward(request,response);

        }
        else if (!passWord.equals(userPass))
        {//密码错误

            request.setAttribute("errorMessage","密码错误");
            request.getRequestDispatcher("/loginError.jsp").forward(request,response);
        }
    }
}

而loginError.jsp:

<%--
  Created by IntelliJ IDEA.
  User: lenovo
  Date: 2018/8/3
  Time: 16:26
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>


   <h2>用户登录错误界面</h2>
<div>
 <%=request.getAttribute("errorMessage")%>
</div>
</body>
</html>

1.对于跳转的代码这是一个格式

request.getRequestDispatcher(要跳转的界面的js代码的地址).forward(request,response)

2.这里要将错误的原因返回给jsp，故要用共享数据。

共享数据，之前的在多个servlrt中，可以用servletContext来，但是，它在并发的情况下回错误。这里要用request.setAttribute()

,request.getAttribute()这两个方法来在两个地方传递/共享数据，它可以满足并发的需要。

web实现登录错误后跳转界面

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