jsp跳转getRequestDispatcher()和sendRedirect()的区别

Shun

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：

<%@ 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">
  用户名:<input type="text" name="username" />
  密码:<input type="password" name="password" />
  <input type="submit" />
  </form>

session.java：

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("https://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：

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