zoukankan      html  css  js  c++  java

  • Servlet 学习（五）

    重定向redirect

    1、使用方法

    • response.sendRedirect("/应用名/ 访问资源名");
    • response.sendRedirect(request.getContextPath() + "/pages/dispatch/index.html");

    2、重定向原理

    重定向中，组件A 的request 和response 不会被组件B 所共享或继续使用使用重定向，浏览器地址栏显式的地址会发生改变！

    3、重定向测试案例

    测试案例：

    <!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Dispatch</title>
</head>
<body>

    <h5>注册</h5>
    <form action="/Servlet/dispatch/regist" method="post" >
        <input type="text" name="username" placeholder="用户名">
        <input type="password" name="password" placeholder="输入密码">
        <input type="password" name="confirm" placeholder="确认密码">
        <input type="submit" value="提交">
    </form>
    
    <hr>
    
    <a href="/Servlet/page/login" >登录</a>
    
</body>

</html>
    <!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>成功</title>
</head>
<body>

    <h1>成功</h1>

</body>
</html>
    package ecut.dispatch.redirect;

import java.io.IOException;
import java.io.PrintWriter;

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

@WebServlet("/dispatch/regist")
public class RegistServlet extends HttpServlet {

    private static final long serialVersionUID = -4191840660711521199L;

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        System.out.println("regist");
        request.setCharacterEncoding("UTF-8");
        response.setCharacterEncoding("UTF-8");
        response.setContentType("text/html;charset=UTF-8");

        // PrintWriter w = response.getWriter();

        String username = request.getParameter("username");
        String password = request.getParameter("password");
        String confirm = request.getParameter("confirm");

        // 判断用户名是否为空 ( 页面上可能根本就没有提交username 、页面提交了空串)
        if (username == null || username.trim().isEmpty()) {
            // 不能注册
            // w.println("<h3>用户名不能为空,3秒后返回首页</h3>");//刷新存在表单再次提交问题，因为地址没有改变还是当前URL，刷新就会再次请求
            // response.setHeader("refresh", "3,URL=" +request.getContextPath() + "/pages/dispatch/index.html"); // 定时跳转
            response.sendRedirect(request.getContextPath() + "/pages/dispatch/index.html");//重定向到了另一个页面解决了表单提交的问题
            return;
        } else {
            // 用户名可能使用，但是需要检查密码是否为空且两次密码输入是否一致
            if (password != null && password.length() != 0 && password.equals(confirm)) {
                // 可以注册
                // w.println( "<h3>注册成功</h3>" );
                response.sendRedirect(request.getContextPath() + "/pages/dispatch/success.html");
                return;
            } else {
                // 没有密码 或 密码输入不一致 不能注册
                // w.println( "<h3>密码输入不正确</h3>" );
                 response.sendRedirect(request.getContextPath() + "/pages/dispatch/index.html");
                return;//响应结束了
            }
        }

    }

}

    运行结果如下：

    输入正确跳转到成功页面，其他情况回到首页

     

    请求调度器RequestDispatche

    1、它是javax.servlet 中的一个接口

    • 使用时的实现类，由Servlet容器提供
    • 该接口中所包含的方法(仅此两个)，forward() 和include()

    2、获取RequestDispatcher 的途径

    • ServletRequest#getRequestDispatcher(String path)
    • ServletContext#getRequestDispatcher(String path)
    • ServletContext#getNamedDispatcher(String name)

    转发forward

    1、使用方法

    • request.getRequestDispatcher("/相对路径<不包含应用名>").forward( request , response );
    • RequestDispatcher dispatcher = request.getRequestDispatcher( "/page/success" );
      dispatcher.forward( request , response );

    2、转发原理

    转发中，组件A 的request 和response 会被组件B 继续使用(被传递过来)，使用转发，浏览器地址栏显式的地址不会发生改变！

     

    3、转发测试案例

    测试案例：

    <!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>登录成功</title>
</head>
<body>
    <h1>登录成功</h1>
</body>
</html>
    package ecut.dispatch.forward;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
//登陆页面
@WebServlet( "/page/login" )
public class LoginPageServlet extends HttpServlet {

    private static final long serialVersionUID = 2075180219363356668L;

    @Override
    protected void service( HttpServletRequest request , HttpServletResponse response ) 
            throws ServletException, IOException {
        request.setCharacterEncoding( "UTF-8" );
        response.setCharacterEncoding( "UTF-8" );
        response.setContentType( "text/html;charset=UTF-8" );
        
        PrintWriter w = response.getWriter();
        
        w.println( "<!DOCTYPE html>" );
        w.println( "<html>" );
        w.println( "<head>" );
        w.println( "<meta charset='UTF-8'>" );
        w.println( "<title>登录</title>" );
        w.println( "</head>" );
        w.println( "<body>" );
        w.println( "    <h5>登录</h5>" );
        
        w.println( "    <form action='" + request.getContextPath() + "/action/login' method='post' >" );
        w.println( "        <input type='text' name='username' placeholder='用户名'>" );
        w.println( "        <input type='password' name='password' placeholder='输入密码'>" );
        w.println( "        <input type='submit' value='登录'>" );
        w.println( "    </form>" );
        
        w.println( "</body>" );
        w.println( "</html>" );
        
    }
    
    

}
    package ecut.dispatch.forward;

import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
//登陆操作
@WebServlet( "/action/login" )
public class LoginActionServlet extends HttpServlet {

    private static final long serialVersionUID = 6978052887387276476L;

    @Override
    protected void service( HttpServletRequest request , HttpServletResponse response ) 
            throws ServletException, IOException {
        request.setCharacterEncoding( "UTF-8" );
        response.setCharacterEncoding( "UTF-8" );
        response.setContentType( "text/html;charset=UTF-8" );
        
        String username = request.getParameter( "username" );
        String password = request.getParameter( "password" );
        
        System.out.println( "username : " + username + " , password : " + password );
        
        if( "zhangsanfeng".equals( username ) && "hello2017".equals( password ) ){
            //RequestDispatcher dispatcher = request.getRequestDispatcher( "/WEB-INF/dispatch/login_success.html" );
            //dispatcher.forward( request , response );//转发到另一个页面，刷新页面存在表单重新提交的问题，因为地址没有改变还是当前URL，刷新就会再次请求再次提交表单
            response.setHeader("suibian", "suibianzhi");
            request.setAttribute("counter", 250);//可以将request当做Map<String , Object>来使用，map.put("counter",250)
            RequestDispatcher dispatcher = request.getRequestDispatcher( "/page/success" );
            dispatcher.forward( request , response );//转发到另一个页面Servlet，刷新页面存在表单重新提交的问题，因为地址没有改变还是当前URL，刷新就会再次请求再次提交表单
            
            //为了解决表单重复提交的问题，可以采取以下方法:
            // 1、重定向到另外的一个 Servlet ，比如 LoginSuccessServlet
            // 2、由 另外的一个 Servlet ，比如 LoginSuccessServlet 完成 转发操作
            //response.sendRedirect(  request.getContextPath() + "/forward/login/success" );//由LoginSuccessServlet去转发
            return ;
        } else {
            response.sendRedirect(  request.getContextPath() + "/page/login" );
            return ;
        }
        
    }
    
    

}
    package ecut.dispatch.forward;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
//登陆页面
@WebServlet( "/page/success" )
public class SuccessPageServlet extends HttpServlet {

    private static final long serialVersionUID = 2075180219363356668L;

    @Override
    protected void service( HttpServletRequest request , HttpServletResponse response ) 
            throws ServletException, IOException {
        request.setCharacterEncoding( "UTF-8" );
        response.setCharacterEncoding( "UTF-8" );
        response.setContentType( "text/html;charset=UTF-8" );
        Object value=request.getAttribute("counter");//可以将request当做Map<String , Object>来使用，map.get("counter")
        System.out.println(value);//用的是同一个请求
        System.out.println(response.getHeader("suibian"));//用的是同一个响应
        PrintWriter w = response.getWriter();
        
        w.println( "<!DOCTYPE html>" );
        w.println( "<html>" );
        w.println( "<head>" );
        w.println( "<meta charset='UTF-8'>" );
        w.println( "<title>登录</title>" );
        w.println( "</head>" );
        w.println( "<body>" );
        w.println( "    <h1>登录成功</h1>" );
        w.println( "</body>" );
        w.println( "</html>" );
        
    }
    
    

}
    package ecut.dispatch.forward;

import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet( "/forward/login/success" )
public class LoginSuccessServlet extends HttpServlet {

    private static final long serialVersionUID = -7565331422887485255L;

    @Override
    protected void service( HttpServletRequest request , HttpServletResponse response ) 
            throws ServletException, IOException {
        request.setCharacterEncoding( "UTF-8" );
        response.setCharacterEncoding( "UTF-8" );
        response.setContentType( "text/html;charset=UTF-8" );
        //这个页面不能被直接访问
        RequestDispatcher dispatcher = request.getRequestDispatcher( "/WEB-INF/dispatch/login_success.html" );
        dispatcher.forward( request , response );
        
    }
    
    

}

    运行结果如下：

    username : AmyZheng , password : 123
250
suibianzhi
username : AmyZheng , password : 
username :  , password :

    转发和重定向的区别

    • Redirect ( 重定向 ) :

    　　　　地址栏:

    　　　　　　从第一个被请求的地址 变成 第二个请求对应的地址
    　　　　客户端发起两次请求:
    　　　　　　第一次请求由 "用户" 主动发起
    　　　　　　第二次请求是由于 浏览器接受到了 来自服务器的 "指示"所以重新发起请求

    　　　　实现：

    　　　　　　重定向通过 response.sendRedirect( location ) 来实现

    • Forward ( 转发 )　　

    　　　　地址栏:

    　　　　　　所请求的路径不会发生变化
    　　　　客户端仅发起一次请求：

    　　　　　　服务器内部完成对请求的组件的调度在 /page/login 对应的页面的登录表单:<form ation = request.getContextPath() +  "/action/l
    　　　　　　ogin"  >，因此点击登陆按钮后会请求 /action/login，而在 /action/login 对应的 Servlet 中:RequestDispatcher dispatcher = req
    　　　　　　uest.getRequestDispatcher( "/WEB-INF/dispatch/login_success.html" );dispatcher.forward( request , response );

    　　　　实现：

    　　　　　　转发通过非静态方法 RequestDispatcher.forward( ServletRequest , ServletResposne ) 方法来实现在转发操作中 ，第一个组件的
    　　　　　　request 和 response 被传递给 第二个组件继续使用:

    包含include

     1、使用方法

    • request.getRequestDispatcher("/相对路径<不包含应用名>"). include(request , response);
    • dispatcher = request.getRequestDispatcher( "/pages/dispatch/header.jsp" );                                                                                                                   dispatcher.include( request , response );

    2、包含原理

    3、包含测试案例

    测试案例一：

    <!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>header</title>
<style type="text/css">
    .header { 
        border: 1px solid #dedede ; 
        box-shadow: 0px 0px 5px 4px #eee ; 
        width : 600px ; 
        margin: 20px auto ;
        height: auto;
        overflow: hidden;
    }
    
    .header span {
        float: left ;
        text-align : center ;
        width: 25% ;
        line-height : 80px ; 
        height : 80px ; 
        box-shadow: 0px 0px 1px 0px blue inset ;
    }
</style>
</head>
<body>

    <div class="header">
        <span>first</span>
        <span>second</span>
        <span>third</span>
        <span>forth</span>
    </div>

</body>
</html>
    package ecut.dispatch.include;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet( "/include/first" )
public class FirstServlet extends HttpServlet {

    private static final long serialVersionUID = 3984166560156790204L;
    
    @Override
    protected void service( HttpServletRequest request , HttpServletResponse response ) 
            throws ServletException, IOException {
        request.setCharacterEncoding( "UTF-8" );
        response.setCharacterEncoding( "UTF-8" );
        response.setContentType( "text/html;charset=UTF-8" );
        //斜杆表示从WebContent算起的路径
        RequestDispatcher dispatcher = request.getRequestDispatcher( "/pages/dispatch/header.html" );
        //jsp就是servlet所以不会报错,因此可以包含多个
        //RequestDispatcher dispatcher = request.getRequestDispatcher( "/pages/dispatch/header.jsp" );

        dispatcher.include( request , response );
        //包含静态资源（HTML页面）的时候，页面输出完，流就结束意味着响应结束，再去输出流就会报错
        //getOutputStream() has already been called for this response,想获得输出流时候但是响应结束了
        PrintWriter w = response.getWriter() ; 
        
        w.println( "<h1>First Servlet</h1>" );
        
    }

}

    运行结果如下：

     

    测试案例二：

    <%@ page language="java"  pageEncoding="UTF-8" %>
<%@ page contentType="text/html; charset=UTF-8" %>

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>header</title>
<style type="text/css">
    .header { 
        border: 1px solid #dedede ; 
        box-shadow: 0px 0px 5px 4px #eee ; 
        width : 600px ; 
        margin: 20px auto ;
        height: auto;
        overflow: hidden;
    }
    
    .header span {
        float: left ;
        text-align : center ;
        width: 25% ;
        line-height : 80px ; 
        height : 80px ; 
        box-shadow: 0px 0px 1px 0px blue inset ;
    }
</style>
</head>
<body>

    <div class="header">
        <span>first</span>
        <span>second</span>
        <span>third</span>
        <span>forth</span>
    </div>

</body>
</html>
    package ecut.dispatch.include;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet( "/include/second" )
public class SecondServlet extends HttpServlet {

    private static final long serialVersionUID = 3984166560156790204L;
    
    @Override
    protected void service( HttpServletRequest request , HttpServletResponse response ) 
            throws ServletException, IOException {
        request.setCharacterEncoding( "UTF-8" );
        response.setCharacterEncoding( "UTF-8" );
        response.setContentType( "text/html;charset=UTF-8" );
        
        RequestDispatcher dispatcher = request.getRequestDispatcher( "/pages/dispatch/header.jsp" );
        dispatcher.include( request , response );
        
        PrintWriter w = response.getWriter() ; 
        
        w.println( "<h1 style='text-align:center;'>Second Servlet</h1>" );
        
        dispatcher = request.getRequestDispatcher( "/pages/dispatch/header.jsp" );
        dispatcher.include( request , response );
        
    }

}

    运行结果如下：

    转发和包含的区别

    •  Forward ( 转发 )

    　　　　转发通过非静态方法 RequestDispatcher.forward( ServletRequest , ServletResposne ) 方法来实现
    　　　　响应有去无回
    　　　　　　web client ---->  A(request,response)
                           　　　　　　  A:forward(request,response)
                           　　　　    　 B(request,response)       --------->web client 

    • Include ( 包含)

    　　　　包含通过非静态方法 RequestDispatcher.include( ServletRequest , ServletResposne ) 方法来实现
    　　　　响应有去有回
    　　　　　　web client ---->  A(request,response)  --------->web client
                           　　　　　　   A:include(request,response)
    　　　　　　　　　　　　　　　　     ^
                            　　　　　　　　　 |
                           　　　　　　　　　  |
                            　　　　　　　　　 |
                      　　　　　　　　　       |
                            　　　　　　　　　 |
                            　　　　　　B(request,response)      

    转载请于明显处标明出处

    http://www.cnblogs.com/AmyZheng/p/8902155.html
  • 相关阅读:
    vue + ElementUI 的横向表格代码
    localStorage.getItem
    字符串分割与数组的分割 split()VSsplice()&slice()
    ES6 Class 的基本语法
    e6 6 Symbol
    ES6 Iterator 和 for...of 循环
    ES6 数组的扩展
    element-ui上传一张图片后隐藏上传按钮
    图片上传预览原理及实现
    Winform的一些控件说明
  • 原文地址：https://www.cnblogs.com/AmyZheng/p/8902155.html
Copyright © 2011-2022 走看看