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发布时间:2016-01-01 作者:网络 阅读:185次

1.request.getRequestDispatcher()是请求转发,前后页面共享一个request ;
response.sendRedirect()是重新定向,前后页面不是一个request。

2.RequestDispatcher.forward()是在服务器端运行;
HttpServletResponse.sendRedirect()是通过向客户浏览器发送命令来完成.
所以RequestDispatcher.forward()对于浏览器来说是“透明的”;
而HttpServletResponse.sendRedirect()则不是。

3.ServletContext.getRequestDispatcher(String url)中的url只能使用绝对路径; 而ServletRequest.getRequestDispatcher(String url)中的url可以使用相对路径。因为ServletRequest具有相对路径的概念;而ServletContext对象无次概念。

RequestDispatcher对象从客户端获取请求request,并把它们传递给服务器上的servlet,html或jsp。它有两个方法:

1.void forward(ServletRequest request,ServletResponse response)

用来传递request的,可以一个Servlet接收request请求,另一个Servlet用这个request请 求来产生response。request传递的请求,response是客户端返回的信息。forward要在response到达客户端之前调用,也 就是 before response body output has been flushed。如果不是的话,它会报出异常。

2.void include(ServletRequest request,ServletResponse response)

用来记录保留request和response,以后不能再修改response里表示状态的信息。

如果需要把请求转移到另外一个Web App中的某个地址,可以按下面的做法:
1. 获得另外一个Web App的ServletConext对象(currentServletContext.getContext(uripath)).

2. 调用ServletContext.getRequestDispatcher(String url)方法。

eg:ServletContext.getRequestDispatcher(“smserror.jsp”).forward(request,response);

代码实例:
index.jsp:
复制代码 代码如下:
<%@ 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





    


  用户名:

  密码:

  
  

session.java:
复制代码 代码如下:
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");
        */
                //这个路径必须是这样写,而不能像上面的request.getRequestDispatcher那样使用相对路径
                //  而且要是使用response.sendRedirect的话在下面的session.jsp中不能通过request.getAttribute来获取request对象
                //因为前后使用的不是同一个request,但是session可以,因为session会一直存在直到用户关闭浏览器
    }

    /**
     * Initialization of the servlet.

     *
     * @throws ServletException if an error occurs
     */
    public void init() throws ServletException {
        // Put your code here
    }

}

getsession.jsp:

复制代码 代码如下:
<%@ 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






    

  <%   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的话就不能获取到name和pwd  
 out.println("name " + name + "pwd "+ pwd);   
  %>

关键字词:JSP编程  

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