javaee中request與response分不清以及請求轉發

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class demo5 extends HttpServlet {

    /**
     *路勁問題：
     *  首先給每個需要寫路徑的地方帶上一個/，然後區分
     * 1）服務器行爲 ：則斜槓就代表是在項目下的地方，需要訪問什麼路勁便可以直接填寫
     * 2）瀏覽器行爲 ：則斜槓就代表是在webapps下，但是不確定是在什麼項目，所以路徑需要先填寫一個項目名
     */
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        //請求轉發，屬於服務器行爲
        request.getRequestDispatcher("/index.jsp").forward(request, response);

        //響應重定向，屬於瀏覽器行爲
        response.sendRedirect("/Myitcast_day05/index.jsp");

        //讀取web應用的文件，屬於服務器行爲
        this.getServletContext().getRealPath("/index.jsp");
        this.getServletContext().getResourceAsStream("/index.jsp");

        //超鏈接，屬於在瀏覽器發送請求，是瀏覽器行爲
        //<a href="/Myitcast_day05/index.jsp">點擊</a>

        //表單提交，也是在瀏覽器發送請求，是瀏覽器行爲
        //<form action="/Myitcast_day05/index.jsp"></form>


    }


    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        doGet(request, response);
    }

}

二、根據在視圖層顯示字符數據

import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class demo6 extends HttpServlet {

    /**
     *顯示數據字符給視圖
    */
        public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

            //告訴瀏覽器以utf-8的形式輸出內容，但是瀏覽器的碼錶卻沒有改
            //所以一般是設置setContentType這個方法，這個方法便可以省略了
            response.setCharacterEncoding("UTF-8");

            //輸出的內容以html形式，text/html也是瀏覽器默認設置的形式
            response.setContentType("text/html;charset=utf-8");

            //輸出響應頭信息content-type爲text/html;charset=utf-8,這個方法是總的方法
            //當輸出了setContentTy這個方法便不用輸出這個
            response.setHeader("content-type","text/html;charset=utf-8");

            //把輸出的內容換成xml的形式輸出
            response.setContentType("text/xml;charset=utf-8");


            //在瀏覽器輸出內容的時候查詢的碼錶是ISO-8859-1，不支持中文，所以需要轉碼錶
            //PrintWriter out = response.getWriter();
            //out.write("暴龍");


            OutputStream out = response.getOutputStream();
            out.write("暴龍".getBytes());   //這個字節碼的形式輸出參照的碼錶是GBK，所以需要轉換爲utf-8來輸出
            out.write("暴龍".getBytes("UTF-8"));
        }


        public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        doGet(request,response);
        }

}

三、在視圖層下載數據給用戶

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class demo7 extends HttpServlet {

    /**
     * 在瀏覽器下載給用戶
     */
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        //讀取服務器發佈的內容，創建成一個文件
        String path = this.getServletContext().getRealPath("/attach/hibernate.zip");
        File file = new File(path);

        //設置響應頭content-disposition來設置下載的形式
        response.setHeader("content-disposition", "attachment; filename="+file.getName());

        //讀文件並按照流的方式輸出
        FileInputStream in = new FileInputStream(file);

        OutputStream out = response.getOutputStream();

        byte[] b = new byte[512];
        int length = 0;
        while((length=in.read())!=1){
            out.write(b, 0, length);
        }

        out.close();
        in.close();
    }


    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        doGet(request, response);
    }

}

四、關於request和response的刷新轉發重定向的問題

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 demo8 extends HttpServlet {

    /**
     * The doGet method of the servlet. <br>
     *
     * 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 {

        //設置響應頭爲refresh，當值爲整數時候，表示當多少秒時該網頁會自動刷新
        response.setHeader("refresh", "3");

        //當值爲整數;url=xxxx，表示當多少秒後會刷新到url指定的頁面
        response.setHeader("refresh", "3;url=/Myitcast_day05/index.jsp");


        //設置響應頭location，表示會轉發到後面指定的url頁面，常常配合狀態碼302
        response.setHeader("location", "/Myitcast_day05/index.jsp");
        response.setStatus(302);


        //整個web應用只有一個servletContext對象，
        //放入ServletContet的數據常駐內存的,一般是不用這個屬性的
        this.getServletContext().setAttribute("p", "9");

        //另一個域對象：HttpServletRequest對象
        //注意：只需要使用1次的數據，可以用request對象共享出去
        request.setAttribute("p", "9");

        //request的請求轉發是可以得到共享數據的，但是response的重定向是不可以的
        request.getRequestDispatcher("/demo4").forward(request, response);
        response.sendRedirect("/Myitcast_day05/demo4");

        //request能夠得到在request域中存放的共享數據
        request.getAttribute("p");

    }


    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        doGet(request, response);
    }

}

最後的總結：

responset的重定向和request的轉發的區別:

請求重定向：

1）瀏覽器一共發出了2次請求

2）瀏覽器行爲

3）地址欄會改變，變成了去到的地址

4）請求重定向不能通過request共享數據

請求轉發：

1）瀏覽器只發出1次請求

2）服務器行爲 

3）地址欄不會改變的！

4）請求轉發可以通過request共享數據