jsp跳转getRequestDispatcher()和sendRedirect()的区别

前端技术 2023/09/04 JSP

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
<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：

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

<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);   
  %>

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