1.request.getRequestDispatcher()是請(qǐng)求轉(zhuǎn)發(fā)，前后頁(yè)面共享一個(gè)request ;
response.sendRedirect()是重新定向，前后頁(yè)面不是一個(gè)request。
2.RequestDispatcher.forward()是在服務(wù)器端運(yùn)行;
HttpServletResponse.sendRedirect()是通過(guò)向客戶(hù)瀏覽器發(fā)送命令來(lái)完成.
所以RequestDispatcher.forward()對(duì)于瀏覽器來(lái)說(shuō)是“透明的”；
而HttpServletResponse.sendRedirect()則不是。
3.ServletContext.getRequestDispatcher(String url)中的url只能使用絕對(duì)路徑； 而ServletRequest.getRequestDispatcher(String url)中的url可以使用相對(duì)路徑。因?yàn)镾ervletRequest具有相對(duì)路徑的概念；而ServletContext對(duì)象無(wú)次概念。
RequestDispatcher對(duì)象從客戶(hù)端獲取請(qǐng)求request，并把它們傳遞給服務(wù)器上的servlet,html或jsp。它有兩個(gè)方法:
1.void forward(ServletRequest request,ServletResponse response)
用來(lái)傳遞request的，可以一個(gè)Servlet接收request請(qǐng)求，另一個(gè)Servlet用這個(gè)request請(qǐng) 求來(lái)產(chǎn)生response。request傳遞的請(qǐng)求，response是客戶(hù)端返回的信息。forward要在response到達(dá)客戶(hù)端之前調(diào)用，也 就是 before response body output has been flushed。如果不是的話(huà)，它會(huì)報(bào)出異常。
2.void include(ServletRequest request,ServletResponse response)
用來(lái)記錄保留request和response，以后不能再修改response里表示狀態(tài)的信息。
如果需要把請(qǐng)求轉(zhuǎn)移到另外一個(gè)Web App中的某個(gè)地址，可以按下面的做法：
1. 獲得另外一個(gè)Web App的ServletConext對(duì)象(currentServletContext.getContext(uripath)).
2. 調(diào)用ServletContext.getRequestDispatcher(String url)方法。
eg:ServletContext.getRequestDispatcher(“smserror.jsp”).forward(request,response);
代碼實(shí)例：
index.jsp：
復(fù)制代碼 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">
用戶(hù)名:input type="text" name="username" />
密碼:input type="password" name="password" />
input type="submit" />
/form>
session.java：
復(fù)制代碼 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(gè)路徑必須是這樣寫(xiě)，而不能像上面的request.getRequestDispatcher那樣使用相對(duì)路徑
// 而且要是使用response.sendRedirect的話(huà)在下面的session.jsp中不能通過(guò)request.getAttribute來(lái)獲取request對(duì)象
//因?yàn)榍昂笫褂玫牟皇峭粋€(gè)request，但是session可以，因?yàn)閟ession會(huì)一直存在直到用戶(hù)關(guān)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：
復(fù)制代碼 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(huà)就不能獲取到name和pwd
out.println("name " + name + "pwd "+ pwd);
%>
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