javaWEB总结(14):请求的转发和重定向
通俗理解请求转发与重定向的流程
通俗的来讲:我们可以把请求转发和重定向当成是一种借钱的情景模式。
(1)请求的转发:A向B借钱，B自己没有钱，但是向C借到了钱，并且把钱借给了A。A只向B请求了一次。
(2)请求的重定向:A向B借钱，B没有钱，A又向C借钱，C将钱借给了A。A向B请求了一次，又向C请求了一次，一共两次请求。
请求转发与重定向的具体过程
请求转发
(1)调用HttpServletRequest的getRequestDispather()方法获取请求转发器对象，调用getRequestDispather()需要传入要转发的地址。
(2)调用HttpServletRequest的forward(request,response)方法，进行请求的转发。
请求重定向
直接HttpServletResponse的sendRedirect方法并传入参数。
请求转发与重定向的java代码实现
请求转发
//要转发的地址
String path = "/forward.jsp";
//转发
request.getRequestDispatcher(path).forward(request, response);
请求重定向
//要重定向的地址
String path = "/redirect.jsp";
//重定向
response.sendRedirect(path);
下面是一个demo
web.xml
<?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_3_0.xsd" id="WebApp_ID" version="3.0">
<display-name>javaWeb_14</display-name>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>index.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!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=UTF-8">
<title>index</title>
</head>
<body>
<br><br>
<a href="forwardServlet?name=666">to forward.jsp</a>
<br><br>
<a href="redirectServlet?name=666">to redirect.jsp</a>
</body>
</html>ForwardServlet.java
package com.dao.chu;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class ForwardServlet
*/
@WebServlet("/forwardServlet")
public class ForwardServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public ForwardServlet() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("ForwardServlet");
String name = request.getParameter("name");
System.out.println("name is :"+name);
//要转发的地址
String path = "/forward.jsp";
//转发
request.getRequestDispatcher(path).forward(request, response);
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
}
}
RedirectServlet.java
package com.dao.chu;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class RedirectServlet
*/
@WebServlet("/redirectServlet")
public class RedirectServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public RedirectServlet() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("RedirectServlet");
String name = request.getParameter("name");
System.out.println("name is :"+name);
//要重定向的地址
String path = "/redirect.jsp";
//重定向
response.sendRedirect(path);
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
}
}
forward.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!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=UTF-8">
<title>forward.jsp</title>
</head>
<body>
<h2>forward.jsp</h2>
<%
String name = request.getParameter("name");
if(null!=name&&!"".equals(name)){
out.print("name is："+name);
}
%>
</body>
</html>
redirect.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!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=UTF-8">
<title>redirect.jsp</title>
</head>
<body>
<h2>redirect.jsp</h2>
<%
String name = request.getParameter("name");
if(null!=name&&!"".equals(name)){
out.print("name is："+name);
}
%>
</body>
</html>运行结果
主界面
点击to forward.jsp
点击to redirect.jsp
控制台
结论
(1)转发到forward.jsp页面的为同一个请求，而重定向到redirect.jsp页面的不是同一个请求；
(2)两次的地址栏不同。
请求转发与重定向区别
(1)转发发送一次请求，而重定向发送两次请求。(本质区别)(2)请求转发:地址栏是初次发送请求的地址；
重定向:地址栏为最后响应的地址。
(3)请求转发:在最终的servlet中，request对象和中转的那个request为同一个对象；
重定向:在最终的servlet中，request对象和中转的那个request不是同一个对象；
(4)请求转发:只能转发给当前WEB应用的资源；
重定向:可以重定向到任何资源；
