转发过程：客户浏览器发送http请求----》web服务器接受此请求--》调用内部的一个方法在容器内部完成请求处理和转发动作----》将目标资源发送给客户；在这里，转发的路径必须是同一个web容器下的url，其不能转向到其他的web路径上去，中间传递的是自己的容器内的request。在客户浏览器路径栏显示的仍然是其第一次访问的路径，也就是说客户是感觉不到服务器做了转发的。转发行为是浏览器只做了一次访问请求。
重定向过程：客户浏览器发送http请求----》web服务器接受后发送302状态码响应及对应新的location给客户浏览器--》客户浏览器发现是302响应，则自动再发送一个新的http请求，请求url是新的location地址----》服务器根据此请求寻找资源并发送给客户。在这里location可以重定向到任意URL，既然是浏览器重新发出了请求，则就没有什么request传递的概念了。在客户浏览器路径栏显示的是其重定向的路径，客户可以观察到地址的变化的。重定向行为是浏览器做了至少两次的访问请求的。
this.getServletContext().getRequestDispatcher("/index.jsp").forward(req, resp);
resp.getWriter().println("hey,I am Rowandjj");
this.getServletContext().getRequestDispatcher("/index.jsp").include(req, resp);显示:
package cn.edu.chd.web;
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("/servlet/Test")
public class Test extends HttpServlet {
private static final long serialVersionUID = 1L;
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException
{
resp.setContentType("text/html;charset=utf-8");
resp.getWriter().println("tomcat 7测试");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException
{
this.doGet(req, resp);
}
}浏览器中输入http://localhost:8080/Tomcat7Test/servlet/Test即可访问(视不同项目名称而定)。
<!DOCTYPE html>
<html>
<head>
<meta charset="US-ASCII">
<title>Login Page</title>
</head>
<body>
<form action="LoginServlet" method="post">
Username: <input type="text" name="user">
<br>
Password: <input type="password" name="pwd">
<br>
<input type="submit" value="Login">
</form>
</body>
</html>如果登陆成功，跳转到下面这个页面：<%@ page language="java" contentType="text/html; charset=US-ASCII"
pageEncoding="US-ASCII"%>
<!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=US-ASCII">
<title>Login Success Page</title>
</head>
<body>
<h3>Hi Rowandjj, Login successful.</h3>
<a href="login.html">Login Page</a>
</body>
</html>下面是web.xml文件中配置的内容：<?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>LoginExample</display-name>
<welcome-file-list>
<welcome-file>login.html</welcome-file>
</welcome-file-list>
<context-param>
<param-name>dbURL</param-name>
<param-value>jdbc:mysql://localhost/mysql_db</param-value>
</context-param>
<context-param>
<param-name>dbUser</param-name>
<param-value>mysql_user</param-value>
</context-param>
<context-param>
<param-name>dbUserPwd</param-name>
<param-value>mysql_pwd</param-value>
</context-param>
</web-app>处理用户登陆请求的servlet如下（servlet采用注解进行配置）：package com.journaldev.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class LoginServlet
*/
@WebServlet(
description = "Login Servlet",
urlPatterns = { "/LoginServlet" },
initParams = {
@WebInitParam(name = "user", value = "Rowandjj"),
@WebInitParam(name = "password", value = "aa")
})
public class LoginServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
public void init() throws ServletException {
//we can create DB connection resource here and set it to Servlet context
if(getServletContext().getInitParameter("dbURL").equals("jdbc:mysql://localhost/mysql_db") &&
getServletContext().getInitParameter("dbUser").equals("mysql_user") &&
getServletContext().getInitParameter("dbUserPwd").equals("mysql_pwd"))
getServletContext().setAttribute("DB_Success", "True");
else throw new ServletException("DB Connection error");
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//get request parameters for userID and password
String user = request.getParameter("user");
String pwd = request.getParameter("pwd");
//get servlet config init params
String userID = getServletConfig().getInitParameter("user");
String password = getServletConfig().getInitParameter("password");
//logging example
log("User="+user+"::password="+pwd);
if(userID.equals(user) && password.equals(pwd)){
response.sendRedirect("LoginSuccess.jsp");
}else{
RequestDispatcher rd = getServletContext().getRequestDispatcher("/login.html");
PrintWriter out= response.getWriter();
out.println("<font color=red>Either user name or password is wrong.</font>");
rd.include(request, response);//这里使用了include，自己体会为什么
}
}
}
好了，这篇文章到此就结束了，下一篇我们将介绍session管理，过滤器以及监听器。原文：http://blog.csdn.net/chdjj/article/details/18862997