1.request.getRequestDispatcher()是請求轉寄，前後頁面共用一個request ;
response.sendRedirect()是重新定向，前後頁面不是一個request。
2.RequestDispatcher.forward()是在伺服器端運行;
HttpServletResponse.sendRedirect()是通過向客戶瀏覽器發送命令來完成.
所以RequestDispatcher.forward()對於瀏覽器來說是“透明的”；
而HttpServletResponse.sendRedirect()則不是。
3.ServletContext.getRequestDispatcher(String url)中的url只能使用絕對路徑； 而ServletRequest.getRequestDispatcher(String url)中的url可以使用相對路徑。因為ServletRequest具有相對路徑的概念；而ServletContext對象無次概念。
RequestDispatcher對象從用戶端擷取請求request，並把它們傳遞給伺服器上的servlet,html或jsp。它有兩個方法:
1.void forward(ServletRequest request,ServletResponse response)
用來傳遞request的，可以一個Servlet接收request請求，另一個Servlet用這個request請 求來產生response。request傳遞的請求，response是用戶端返回的資訊。forward要在response到達用戶端之前調用，也 就是 before response body output has been flushed。如果不是的話，它會報出異常。
2.void include(ServletRequest request,ServletResponse response)
用來記錄保留request和response，以後不能再修改response裡表示狀態的資訊。
如果需要把請求轉移到另外一個Web App中的某個地址，可以按下面的做法：
1. 獲得另外一個Web App的ServletConext對象(currentServletContext.getContext(uripath)).
2. 調用ServletContext.getRequestDispatcher(String url)方法。
eg:ServletContext.getRequestDispatcher(“smserror.jsp”).forward(request,response);
代碼執行個體：
index.jsp：
複製代碼 代碼如下:
<%@ page language="java" import="java.util.*" pageEncoding="GBK"%>
<% String path = request.getContextPath(); String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; %>
My JSP 'index.jsp' starting page
<meta http-equiv="pragma" content="no-cache" />
<meta http-equiv="cache-control" content="no-cache" />
<meta http-equiv="expires" content="0" />
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3" />
<meta http-equiv="description" content="This is my page" />
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
<form action="servlet/session" method="post">
使用者名稱:<input type="text" name="username" />
密碼:<input type="password" name="password" />
<input type="submit" />
</form>
session.java：
複製代碼 代碼如下:
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class session extends HttpServlet {
/**
* Constructor of the object.
*/
public session() {
super();
}
/**
* Destruction of the servlet.
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
}
/**
* The doGet method of the servlet.
*
* This method is called when a form has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doPost(request, response);
}
/**
* The doPost method of the servlet.
*
* This method is called when a form has its tag value method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String username = "";
String password = "";
username = request.getParameter("username");
password = request.getParameter("password");
HttpSession session = request.getSession();
session.setAttribute("username", username);
session.setAttribute("password", password);
request.setAttribute("name", username);
request.setAttribute("pwd", password);
RequestDispatcher dis = request.getRequestDispatcher("/getsession.jsp");
dis.forward(request, response);
/*
response.sendRedirect("http://localhost:8080/sessiontest/getsession.jsp");
*/
//這個路徑必須是這樣寫，而不能像上面的request.getRequestDispatcher那樣使用相對路徑
// 而且要是使用response.sendRedirect的話在下面的session.jsp中不能通過request.getAttribute來擷取request對象
//因為前後使用的不是同一個request，但是session可以，因為session會一直存在直到使用者關閉瀏覽器
}
/**
* Initialization of the servlet.
*
* @throws ServletException if an error occurs
*/
public void init() throws ServletException {
// Put your code here
}
}
getsession.jsp：
複製代碼 代碼如下:
<%@ page language="java" import="java.util.*" pageEncoding="GBK"%>
<% String path = request.getContextPath(); String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; %>
My JSP 'getsession.jsp' starting page
<meta http-equiv="pragma" content="no-cache" />
<meta http-equiv="cache-control" content="no-cache" />
<meta http-equiv="expires" content="0" />
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3" />
<meta http-equiv="description" content="This is my page" />
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
<% out.print(""); String username = (String)session.getAttribute("username");
String password = (String)session.getAttribute("password");
String name = (String)request.getAttribute("name");
String pwd = (String)request.getAttribute("pwd");
out.println("username " + username + " password " +password);
//如果上面是使用response.sendRedirect的話就不能擷取到name和pwd
out.println("name " + name + "pwd "+ pwd);
%>
