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sendRedirect和RequestDispatcher的區(qū)別？

sendRedirect和RequestDispatcher的區(qū)別：
馬克- to-win：馬克 java社區(qū)：防盜版實名手機尾號： 73203。
馬克-to-win：response.sendRedirect()與request.getRequestDispatcher().forward ()區(qū)別：response.sendRedirect(url)是先回到客戶端，再重新請求url，和過去的請求沒關(guān)系。可以訪問任何地方。瀏覽器的地址欄也變成了新的url。request.getRequestDispatcher().forward()就干脆沒回到客戶端，就一直在服務(wù)器里，從本個web應(yīng)用的一個資源（servlet，jsp，或html）跳到另一個資源。（所以不能隨便訪問什么地方）。而且瀏覽器地址欄沒有變。同時可以用request.setAttribute("requestkey","requstvalue1");來傳遞參數(shù)。
以上幾點是大家經(jīng)常談到的幾點不同。底下就是我專門(exclusively)寫給大家的，一點不
同。也許初學(xué)者難于理解，望留點印象。

RequestDispatcher會block，因為同在服務(wù)器端。當程序需要從資源1跳到資源2時，資源1
會等資源2運行完，回來以后，再繼續(xù)執(zhí)行下面沒執(zhí)行的部分。所謂的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("這里會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");
    }
}


當運行ServletHello1時，console的輸出是：

ServletHello1 before
ServletHello2
這里會block5秒，ServletHello1 after



換做response做實驗：

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("這里不會block5秒，立即運行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");
    }
}


內(nèi)置瀏覽器有bug，換成火狐以后實驗：
地址欄輸入： localhost:8080/ServletHello/MarkToWinServlet


eclipse的console內(nèi)的輸出結(jié)果是：

ServletHello1 before
這里不會block5秒，立即運行ServletHello1 after
ServletHello2