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jsp跳轉(zhuǎn)getRequestDispatcher()和sendRedirect()的區(qū)別

 更新時(shí)間:2014年04月23日 09:47:39   作者:  
這篇文章主要介紹了jsp跳轉(zhuǎn)getRequestDispatcher()和sendRedirect()的區(qū)別,需要的朋友可以參考下

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()是通過向客戶瀏覽器發(fā)送命令來完成.
所以RequestDispatcher.forward()對(duì)于瀏覽器來說是“透明的”;
而HttpServletResponse.sendRedirect()則不是。

3.ServletContext.getRequestDispatcher(String url)中的url只能使用絕對(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)象無次概念。

RequestDispatcher對(duì)象從客戶端獲取請(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) 求來產(chǎn)生response。request傳遞的請(qǐng)求,response是客戶端返回的信息。forward要在response到達(dá)客戶端之前調(diào)用,也 就是 before response body output has been flushed。如果不是的話,它會(huì)報(bào)出異常。

2.void include(ServletRequest request,ServletResponse response)

用來記錄保留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,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的話在下面的session.jsp中不能通過request.getAttribute來獲取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的話就不能獲取到name和pwd  
 out.println("name " + name + "pwd "+ pwd);   
  %>

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