jsp跳转getRequestDispatcher()和sendRedirect()的区别

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:<input type="text" name="username" />

密码:<input type="password" name="password" />

</form>

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);