笔记-JavaWeb学习之旅11

时间 2019-12-14

标签笔记 javaweb 学习之旅栏目 Java 繁體版

原文原文链接

请求转发：一种在服务器内部的资源跳转方式

使用步骤html

1.经过request对象获取请求转发器对象：RequestDispatcher getRequestDispatcher(String path)参数是转发资源的路径java

2.使用Requestispatcher对象进行转发web

特色：浏览器地址栏路径不会发生变化，只能转发当前服务器内部资源，转发是一次请求浏览器

共享数据

域对象：一个有做用范围的对象，能够在范围内共享数据缓存

request域：表明一次请求的范围，通常用于请求转发的多个资源中共享数据服务器

方法：dom

void setAttribute(String name,Object obj):存储数据
Object getAttiude(Stirng name):经过键获取值
void removeAttribute(String name):经过键移除键值对

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对象的方法setAttribute将数据存储到request域中
        request.setAttribute("msg","Hello");
        System.out.println("RequestDemo1被访问了。。。。");
        //转发到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 {
        //访问共享数据,经过键获取值
        System.out.println(request.getAttribute("msg"));
        System.out.println("RequestDemo2被访问了。。。");
    }
}

RequestDemo1被访问了。。。。
Hello
RequestDemo2被访问了。。。

获取ServletContext:ide

ServletContext getServletContext()post

HTTP响应消息

服务器端发送给客户端的数据this

五种数据格式

1.响应行

1：组成：协议/版本响应状态吗状态码描述

2.响应状态码：服务器告诉客户端浏览器本次请求和响应的一个状态，状态码都是3位数字有5种状态码

1xx :服务器接收客户端消息，但没有接收完成，等待一段时间后，发送1xx多状态码

2xx ：成功。表明数字：200

3xx ：重定向。表明：302(重定向)，304(访问缓存)

4xx ：客户端错误。表明(404)请求路径没有对应的资源，405(请求方式没有对应的doxxx方法)

5xx : 服务端错误。表明：500（服务器内部出现异常，好比代码有错）

2.响应头

格式：头名称：值

常见的响应头

Content-Type:服务器告诉客户端本次响应体数据格式以继编码格式

Content-dispostition:服务器告诉客户端以什么格式打开响应体数据

3.响应空行

4响应体：传输的数据

重定向：资源跳转方式

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
        //设置状态码为302
        //response.setStatus(302);
        //设置响应头,头的名称，头的值
        //response.setHeader("location","/Demo2");
        //重定向能够访问其余站点资源
        //response.sendRedirect("https://www.baidu.com");//访问了百度
        //重定向
        response.sendRedirect("/Demo2");
        //设置共享数据
        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 {
        //重定向能够访问其余站点的资源
        System.out.println("demo2.....");
        //重定向不能访问共享数据
        Object o1 = request.getAttribute("msg");
        System.out.println(o1);
    }
}

输出结果

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

重定向的特色：redirect

地址栏发生变化
重定向能够访问其它站点服务器的资源
重定向是两次请求，，不拿使用request对象来共享数据

路径写法

相对路径：经过相对路径不能够肯定惟一资源

绝对路径: 经过绝对路径能够肯定惟一资源，给客户端浏览器使用须要加虚拟目录，给服务器使用，不须要加虚拟目录

服务器输出字符数据到浏览器

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 {
        //使用响应头，告诉浏览器我使用的编码
        //浏览器收到响应，就会按照指定字符集解码
        response.setContentType("text/html;charset=utf-8");
        //response.setHeader("content-type","text/html;charset=utf-8");
        //向客户端输出数据,先要获取字符输出流
        PrintWriter writer = response.getWriter();
        writer.write("<h1>你好,world</h1>");
    }
}

服务器输出字节数据到浏览器

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，客户端".getBytes("utf-8"));
    }
}

验证码

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;
        //建立对象，该对象能够在内存中生成图片
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        //美化图片
        //填充背景色
        Graphics g = image.getGraphics();
        g.setColor(Color.PINK);
        g.fillRect(0,0,width,height);
        //画边框
        g.setColor(Color.BLUE);
        g.drawRect(0,0,width-1,height-1);
        String str="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";

            //  写验证码
        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);
        }


        //将图片输出到页面上
        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：
        //     点击超连接或者图片，须要换一张，
        //     给图片和超连接绑定单击事件
        window.onload=function () {
            //获取图片对象
            var img=document.getElementById("change");
            //绑定单击事件
            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？换一张</a>
</body>
</html>

ServletContext对象：

1.概念：表明整个web应用，能够和程序的容器来通讯

获取方式：

1.request.getServletContext();

2.this.getServletContext();

功能:获取MIME类型（在互联网通讯过程种定义的一种文件数据类型，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 {
        //获取MIME类型
        ServletContext context=this.getServletContext();
        //定义文件名称
        String filename = "a.jpg";
        //获取MIME类型
        String mimeType = context.getMimeType(filename);
        System.out.println(mimeType);
    }
}

//image/jpeg

功能：域对象，共享数据

域对象的方法

setArrtibute(String name,Object value)

getAttribute(String name)

removeAttribute(String name)

功能：获取文件服务器路径

文件在项目目录下，能够直接文件名获取路径
在WEB-INF目录下，须要加上WEB-INF才能够获取
src目录下的全部文件未来都存放在/WEB-INF/classes目录下

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 {
        //获取web目录下的资源访问
        ServletContext context = this.getServletContext();
        String realPath = context.getRealPath("/b.txt");//b.txt在项目目录下，能够直接文件名获取路径
        System.out.println(realPath);
        //获取WEB-INF目录下的资源访问
        String realPath1 = context.getRealPath("/WEB-INF/c.txt");//c.txt在WEB-INF目录下，须要加上WEB-INF才能够获取到路径
        System.out.println(realPath1);
        //获取src目录下的资源能路径
        String realPath2 = context.getRealPath("/WEB-INF/classes/a.txt");//src目录下的全部文件未来都存放在/WEB-INF/classes目录下
        System.out.println(realPath2);
    }
}