请求派发与重定向相同点：
两者均能指向内部地址，在网页设计中经常遇到这种场景，如在登录过程中判断用户是否登陆过，如果没登录过，则可以指向登录界面
请求派发与重定向不同点：
1.请求指派只能指派到内部地址，而重定向既可以指派的内部地址又可以指派到外部地址。
2.请求指派指派过程中url不变，用户无法感知，重定向url会改变
请求派发与重定向实现语法：
1.请求派发
其中url即可以是绝对路径又可以是相对路径request.getRequestDispatcher(url).forward(request, response);2.重定向
之中url如果指向内部地址则只能是相对路径response.sendRedirect(url);
理论再多不如代码理解：
我将实现从page1.html,点击按钮submit,请求派发或重定向到page2.html的案例实现，如下图
先看下html的实现
page1代码：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
body{
background-color: lightgreen;
}
h1{
color: white;
}
</style>
</head>
<body>
<h1>this is page one</h1>
<form action="../first2.do" method="get">
<input type="submit" value="submit">
</form>
</body>
</html>
page2代码：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
body{
background-color: purple;
}
h1{
color: white;
}
</style>
</head>
<body>
<h1>this is page two</h1>
</body>
</html>FirstServlet代码（是已请求派送的方式实现）：
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;
@WebServlet("/first.do")
public class FirstServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//请求指派 HttpServletRequest getRequestDispatcher(url)方法
request.getRequestDispatcher("/html/page2.html").forward(request, response);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}
FirstServlet2代码（是重定向方式实现,这里要修改page1.html表单的action属性action="../first2.do"）：
package com.sxt.web.servlet;
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;
@WebServlet("/first2.do")
public class FirstServlet2 extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//重定向 HttpServletResponse sendRedirect(url)方法
//response.sendRedirect("http://www.baidu.com");//指向外部地址
response.sendRedirect("html/page2.html"); //指向内部地址，只能用相对路径
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}
个人总结，有不对的地方请指出，多谢指教！
结语:No metter hao far you may fly , don't forgrt where you come from.