筆記-JavaWeb學習之旅11

時間 2019-12-14

標籤筆記 javaweb 學習之旅欄目 Java 简体版

原文原文鏈接

請求轉發：一種在服務器內部的資源跳轉方式

使用步驟html

1.經過request對象獲取請求轉發器對象：RequestDispatcher getRequestDispatcher(String path)參數是轉發資源的路徑java

2.使用Requestispatcher對象進行轉發web

特色：瀏覽器地址欄路徑不會發生變化，只能轉發當前服務器內部資源，轉發是一次請求瀏覽器

共享數據

域對象：一個有做用範圍的對象，能夠在範圍內共享數據緩存

request域：表明一次請求的範圍，通常用於請求轉發的多個資源中共享數據服務器

方法：dom

void setAttribute(String name,Object obj):存儲數據
Object getAttiude(Stirng name):經過鍵獲取值
void removeAttribute(String name):經過鍵移除鍵值對

package com.Data.HttpServlet;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;


@WebServlet("/requestDemo1")
public class RequestDemo1 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //使用request對象的方法setAttribute將數據存儲到request域中
        request.setAttribute("msg","Hello");
        System.out.println("RequestDemo1被訪問了。。。。");
        //轉發到requestDemo2
        RequestDispatcher requestDispatcher = request.getRequestDispatcher("/requestDemo2");
        requestDispatcher.forward(request,response);
    }
}

package com.Data.HttpServlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;


@WebServlet("/requestDemo2")
public class RequestDemo2 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //訪問共享數據,經過鍵獲取值
        System.out.println(request.getAttribute("msg"));
        System.out.println("RequestDemo2被訪問了。。。");
    }
}

RequestDemo1被訪問了。。。。
Hello
RequestDemo2被訪問了。。。

獲取ServletContext:ide

ServletContext getServletContext()post

HTTP響應消息

服務器端發送給客戶端的數據this

五種數據格式

1.響應行

1：組成：協議/版本響應狀態嗎狀態碼描述

2.響應狀態碼：服務器告訴客戶端瀏覽器本次請求和響應的一個狀態，狀態碼都是3位數字有5種狀態碼

1xx :服務器接收客戶端消息，但沒有接收完成，等待一段時間後，發送1xx多狀態碼

2xx ：成功。表明數字：200

3xx ：重定向。表明：302(重定向)，304(訪問緩存)

4xx ：客戶端錯誤。表明(404)請求路徑沒有對應的資源，405(請求方式沒有對應的doxxx方法)

5xx : 服務端錯誤。表明：500（服務器內部出現異常，好比代碼有錯）

2.響應頭

格式：頭名稱：值

常見的響應頭

Content-Type:服務器告訴客戶端本次響應體數據格式以繼編碼格式

Content-dispostition:服務器告訴客戶端以什麼格式打開響應體數據

3.響應空行

4響應體：傳輸的數據

重定向：資源跳轉方式

package com.data;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/Demo1")
public class ResponseServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("demo1....");
        //完成重定向
        //設置狀態碼爲302
        //response.setStatus(302);
        //設置響應頭,頭的名稱，頭的值
        //response.setHeader("location","/Demo2");
        //重定向能夠訪問其餘站點資源
        //response.sendRedirect("https://www.baidu.com");//訪問了百度
        //重定向
        response.sendRedirect("/Demo2");
        //設置共享數據
        request.setAttribute("msg","hello");

    }
}

package com.data;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/Demo2")
public class ResponseServlet2 extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //重定向能夠訪問其餘站點的資源
        System.out.println("demo2.....");
        //重定向不能訪問共享數據
        Object o1 = request.getAttribute("msg");
        System.out.println(o1);
    }
}

輸出結果

demo1....
demo2.....
null

重定向的特色：redirect

地址欄發生變化
重定向能夠訪問其它站點服務器的資源
重定向是兩次請求，，不拿使用request對象來共享數據

路徑寫法

相對路徑：經過相對路徑不能夠肯定惟一資源

絕對路徑: 經過絕對路徑能夠肯定惟一資源，給客戶端瀏覽器使用須要加虛擬目錄，給服務器使用，不須要加虛擬目錄

服務器輸出字符數據到瀏覽器

package com.data;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet("/Demo3")
public class ResponseServlet3 extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //使用響應頭，告訴瀏覽器我使用的編碼
        //瀏覽器收到響應，就會按照指定字符集解碼
        response.setContentType("text/html;charset=utf-8");
        //response.setHeader("content-type","text/html;charset=utf-8");
        //向客戶端輸出數據,先要獲取字符輸出流
        PrintWriter writer = response.getWriter();
        writer.write("<h1>你好,world</h1>");
    }
}

服務器輸出字節數據到瀏覽器

package com.data;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet("/Demo3")
public class ResponseServlet3 extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       response.setContentType("text/html;charset=utf-8");
       ServletOutputStream outputStream = response.getOutputStream();
       outputStream.write("你好，客戶端".getBytes("utf-8"));
    }
}

驗證碼

package com.data;


import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

@WebServlet("/Demo4")
public class CheckCodeServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        int width = 100;
        int height = 50;
        //建立對象，該對象能夠在內存中生成圖片
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        //美化圖片
        //填充背景色
        Graphics g = image.getGraphics();
        g.setColor(Color.PINK);
        g.fillRect(0,0,width,height);
        //畫邊框
        g.setColor(Color.BLUE);
        g.drawRect(0,0,width-1,height-1);
        String str="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";

            //  寫驗證碼
        Random ran = new Random();
        for(int i = 1;i<=4;i++){
            int index = ran.nextInt(str.length());
            char ch = str.charAt(index);
            g.drawString(ch+"",width/5*i,height/2);
        }
        g.setColor(Color.GREEN);
        for (int i = 0 ; i< 10 ;i++){
            int x1 = ran.nextInt(width);
            int x2 = ran.nextInt(width);

            int y1 = ran.nextInt(height);
            int y2 = ran.nextInt(height);
            g.drawLine(x1,y1,x2,y2);
        }


        //將圖片輸出到頁面上
        ImageIO.write(image,"jpg",resp.getOutputStream());

    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

    }
}

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        // 分析：
        //     點擊超連接或者圖片，須要換一張，
        //     給圖片和超連接綁定單擊事件
        window.onload=function () {
            //獲取圖片對象
            var img=document.getElementById("change");
            //綁定單擊事件
            img.onclick=function () {
               var date =new Date().getTime();
                img.src="/day14/Demo4"+date;
            }
        }
    </script>
</head>
<body>
    <img id="checkCode" src="/day14/Demo4" />
    <a id="change" href="">看不清？換一張</a>
</body>
</html>

ServletContext對象：

1.概念：表明整個web應用，能夠和程序的容器來通訊

獲取方式：

1.request.getServletContext();

2.this.getServletContext();

功能:獲取MIME類型（在互聯網通訊過程種定義的一種文件數據類型，不如text/html,image/jpeg）

package com.data;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;


@WebServlet("/Demo5")
public class ServletDemo5 extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //獲取MIME類型
        ServletContext context=this.getServletContext();
        //定義文件名稱
        String filename = "a.jpg";
        //獲取MIME類型
        String mimeType = context.getMimeType(filename);
        System.out.println(mimeType);
    }
}

//image/jpeg

功能：域對象，共享數據

域對象的方法

setArrtibute(String name,Object value)

getAttribute(String name)

removeAttribute(String name)

功能：獲取文件服務器路徑

文件在項目目錄下，能夠直接文件名獲取路徑
在WEB-INF目錄下，須要加上WEB-INF才能夠獲取
src目錄下的全部文件未來都存放在/WEB-INF/classes目錄下

package com.data;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;


@WebServlet("/Demo5")
public class ServletDemo5 extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //獲取web目錄下的資源訪問
        ServletContext context = this.getServletContext();
        String realPath = context.getRealPath("/b.txt");//b.txt在項目目錄下，能夠直接文件名獲取路徑
        System.out.println(realPath);
        //獲取WEB-INF目錄下的資源訪問
        String realPath1 = context.getRealPath("/WEB-INF/c.txt");//c.txt在WEB-INF目錄下，須要加上WEB-INF才能夠獲取到路徑
        System.out.println(realPath1);
        //獲取src目錄下的資源能路徑
        String realPath2 = context.getRealPath("/WEB-INF/classes/a.txt");//src目錄下的全部文件未來都存放在/WEB-INF/classes目錄下
        System.out.println(realPath2);
    }
}

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