两种跳转方式

1）请求转发Forward——URL不跳转

登陆错误时候显示错误界面

2）请求重定向Redirect——URL跳转

案例：登陆后跳转网站首页

loginError.jsp

<%--
  Created by IntelliJ IDEA.
  User: 18582
  Date: 2020/3/11
  Time: 16:17
  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>
</body>
<center>
    <h2>用户登陆错误界面</h2>
    <%=request.getAttribute("errorMessage")%>
</center>
</html>

LoginSerblet.java

package net.pp.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 = "chuchu";
        String userPass = "123456";

        String name = request.getParameter("name");
        String passWord = request.getParameter("passWord");

        //请求转发
        if(!name.equals(userName)){
            //账户不存在
            request.setAttribute("errorMessage", "账户不存在");
            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);
        }else{
            //重定向——跳转后注意，访问地址加上项目地址
            // 法一
//            response.setStatus(HttpServletResponse.SC_MOVED_TEMPORARILY);
//            response.setHeader("location", "https://www.baidu.com/");
            //法二
            response.sendRedirect("/hello/home.html");

        }
    }
}

结果如下：

3.自动刷新

index.jsp

<%--
  Created by IntelliJ IDEA.
  User: 18582
  Date: 2020/3/9
  Time: 17:50
  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>
  <%=request.getAttribute("message")%>
  </body>
</html>

RefreshServlet.java

package net.pp.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 = "RefreshServlet", urlPatterns = "/refresh")
public class RefreshServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //JSP中实现自动刷新
        String message = "<meta http-equiv='refresh' content='3;url=/hello/home.html'>3秒后自动跳转到首页，如果没有跳转，请点击<a href='/hello/home.html'>跳转链接</a>";
        request.setAttribute("message", message);
        request.getRequestDispatcher("/index.jsp").forward(request, response);

    }

    //自动刷新
    private void RefreshDemo(HttpServletResponse response) throws IOException {
        response.setContentType("text/html;charset=utf-8");
        response.setHeader("refresh", "3;url='/hello/home.html'");
        response.getWriter().print("3s后自动刷新");
    }
}

结果是：