sendRedirect和RequestDispatcher的区别？

sendRedirect和RequestDispatcher的区别：
马克- to-win：马克 java社区：防盗版实名手机尾号： 73203。
马克-to-win：response.sendRedirect()与request.getRequestDispatcher().forward ()区别：response.sendRedirect(url)是先回到客户端，再重新请求url，和过去的请求没关系。可以访问任何地方。浏览器的地址栏也变成了新的url。request.getRequestDispatcher().forward()就干脆没回到客户端，就一直在服务器里，从本个web应用的一个资源（servlet，jsp，或html）跳到另一个资源。（所以不能随便访问什么地方）。而且浏览器地址栏没有变。同时可以用request.setAttribute("requestkey","requstvalue1");来传递参数。
以上几点是大家经常谈到的几点不同。底下就是我专门(exclusively)写给大家的，一点不
同。也许初学者难于理解，望留点印象。

RequestDispatcher会block，因为同在服务器端。当程序需要从资源1跳到资源2时，资源1
会等资源2运行完，回来以后，再继续执行下面没执行的部分。所谓的block。

例：3.4.1

package com;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ServletHello1 extends HttpServlet {
    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        System.out.println("ServletHello1 before");
        request.getRequestDispatcher("/ServletHello2").forward(request,
                response);
        System.out.println("这里会block5秒，ServletHello1 after");
    }
}



package com;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ServletHello2 extends HttpServlet {
    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("ServletHello2");
    }
}


当运行ServletHello1时，console的输出是：

ServletHello1 before
ServletHello2
这里会block5秒，ServletHello1 after



换做response做实验：

例：3.4.2

package com;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ServletHello1 extends HttpServlet {
    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        System.out.println("ServletHello1 before");
        //request.getRequestDispatcher("/ServletHello2").forward(request,response);
          response.sendRedirect("http://localhost:8080/ServletHello/ServletHello2");
        System.out.println("这里不会block5秒，立即运行ServletHello1 after");
    }
}




package com;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ServletHello2 extends HttpServlet {
    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("ServletHello2");
    }
}


内置浏览器有bug，换成火狐以后实验：
地址栏输入： localhost:8080/ServletHello/MarkToWinServlet


eclipse的console内的输出结果是：

ServletHello1 before
这里不会block5秒，立即运行ServletHello1 after
ServletHello2