JavaWeb重定向与请求转发的区别和执行流程

区别

序号	问题	重定向	请求转发
1	第二次请求谁请求的？	浏览器	服务器
2	浏览器发送了几次请求？	2次以上	1次
3	servlet可以共享request吗？	不可以	可以
4	地址栏是否发生改变？	是	不是
5	浏览器地址栏显示的哪一次访问地址？	最后一次	第一次
6	可以跳转到什么资源？	任意资源	项目内部
7	第二次的请求路径是？	绝对路径	内部路径

现实生活的例子

重定向

①：A对B说，帮忙拿下快递
②：B对A说，没有空，你找下C吧
③：A对C说，帮忙拿下快递
④：C然后拿了快递给A

请求转发

①：A对B说，帮忙拿下快递
②：第二步，B没有空，直接找让C帮A拿下快递
③：C拿到了快递并返回给A

重定向-流程图、代码、结果

1.流程图

2.1代码BoyServlet

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

public class BoyServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 获取请求携带的id
        String id = request.getParameter("id");
        System.out.println("A对B说：帮我拿下快递,id号是:" + id);
        System.out.println("B对A说：我没有空，你找下C");
        System.out.println("----分割线----");
        // 重定向方式1：
        response.setStatus(302);
        response.setHeader("location", "/redirect/girl");
        // 重定向方式2：(正常用此方法)
        // response.sendRedirect("/redirect/girl");
    }

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

}

2.2代码GirlServlet

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

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

public class GirlServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //设置浏览器解析的格式，否则浏览器会出现乱码
        response.setContentType("text/html;charset=utf-8");
        //获取请求携带的id
        String id = request.getParameter("id");
        System.out.println("A对C说，帮我拿下快递，id号是："+id);
        System.out.println("拿到快递了");
        //获取输出流
        PrintWriter writer = response.getWriter();
        //将信息返回给浏览器
        writer.println("拿到快递了");
    }

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

}

2.3web.xml文件

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>redirect</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <description></description>
    <display-name>BoyServlet</display-name>
    <servlet-name>BoyServlet</servlet-name>
    <servlet-class>com.redirect.BoyServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>BoyServlet</servlet-name>
    <url-pattern>/boy</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>GirlServlet</display-name>
    <servlet-name>GirlServlet</servlet-name>
    <servlet-class>com.redirect.GirlServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>GirlServlet</servlet-name>
    <url-pattern>/girl</url-pattern>
  </servlet-mapping>
</web-app>

3.结果

3.1浏览器输入

3.2浏览器返回结果

3.3控制台打印结果

请求转发-流程图、代码、结果

1.流程图

2.1代码BoyServlet

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;

public class BoyServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 获取请求携带的id
        String id = request.getParameter("id");
        System.out.println("A对B说：帮我拿下快递,id号是:" + id);
        System.out.println("B对A说：好的");
        System.out.println("----分割线----");
        //---后面B直接在服务器将请求转发给C---
        //获取转发对象，后面括号指定了转发的路径
        RequestDispatcher dispatcher = request.getRequestDispatcher("/girl");
        //执行转发功能，并将请求和响应一并转发过去
        dispatcher.forward(request, response);

    }

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

}

2.2代码GirlServlet

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

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

public class GirlServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 设置浏览器解析的格式，否则浏览器会出现乱码
        response.setContentType("text/html;charset=utf-8");
        // 获取请求携带的id
        String id = request.getParameter("id");
        System.out.println("B对C说：帮A拿下快递，id号是：" + id);
        System.out.println("拿到快递了");
        // 获取输出流
        PrintWriter writer = response.getWriter();
        // 将信息返回给浏览器
        writer.println("拿到快递了");
    }

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

}

2.3web.xml文件

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>dispatcher</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <description></description>
    <display-name>BoyServlet</display-name>
    <servlet-name>BoyServlet</servlet-name>
    <servlet-class>com.dispatcher.BoyServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>BoyServlet</servlet-name>
    <url-pattern>/boy</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>GirlServlet</display-name>
    <servlet-name>GirlServlet</servlet-name>
    <servlet-class>com.dispatcher.GirlServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>GirlServlet</servlet-name>
    <url-pattern>/girl</url-pattern>
  </servlet-mapping>
</web-app>

3.结果

3.1浏览器输入

3.2浏览器返回结果

3.3控制台结果