JavaWeb-2020/7/31-Response

Response

输出字节数据

• 步骤

  1. 获取字节输出流

  2. 输出数据

package cn.itcast.web.servlet;

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

public class demo4 extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //设置字符编码
        response.setContentType("text/html;charset=utf-8");

        //1.获取字节输出流
        ServletOutputStream sos = response.getOutputStream();
        //2.输出数据
        sos.write("你好".getBytes("utf-8"));
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

基本上和字符输出一致，只不过使用方法不同

验证码

1. 本质：图片

2. 目的： 防止恶意表单注册

演示

package cn.itcast.web.servlet;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
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;

public class CheckCodeServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.创建一个对象，在内存中图片(验证码的图片对象)
        int width=100;
        int height=50;

        BufferedImage image=new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
        //2.美化图片
        //2.1 填充背景色
        Graphics g = image.getGraphics();//画笔对象
        g.setColor(Color.pink);//设置画笔颜色
        g.fillRect(0,0,width,height);
        //2.2 画边框
        g.setColor(Color.BLUE);
        g.drawRect(0,0,width-1,height-1);

        String str="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
        //生成随机角标
        Random ran=new Random();

        for (int i=1;i<=4;i++){
            int index = ran.nextInt(str.length());
            //获取字符
            char ch = str.charAt(index);//随即字符
            //2.3 写验证码
            g.drawString(ch+"",width/5*i,height/2);
        }

        //2.4画干扰线
        g.setColor(Color.GREEN);

        //随机生成坐标点
        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,x2,y1,y2);
        }
        
        //3.将图片输出到页面展示
        ImageIO.write(image,"jpg",response.getOutputStream());

    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

这样我们每刷新一次就会变一次

ServletContext对象

1. 概念：代表整个web应用，可以和程序的容器(服务器)来通信

2. 获取：

   1. 通过request对象来获取 request.getServletContext();

   2. 通过HttpServlet获取 this.getServletContext();

3. 功能：

   1. 获取MIME类型

      • MIME类型：在互联网通信过程中定义的一种文件数据类型

      • 格式： 大类型/小类型 text/html image/jpeg

      • 获取：String getMimeType(String file)

   2. 域对象：共享数据

      1. setAttribute(String name,Object value)

      2. getAttribute(String name)

      3. removeAttribute(String name)

   3. 获取文件的真实(服务器)路径

获取

package cn.itcast.web.servletcontext;

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

public class Context1 extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        /**ServletContext对象获取
         * 1.通过request对象获取
         * request.getServletContext();
         * 2. 通过HttpServlet获取
         * this.getServletContext();
         */

        //1. 通过request对象获取
        ServletContext context1= request.getSession().getServletContext();
        //2. 通过HttpServlet获取
        ServletContext context2 = this.getServletContext();

        System.out.println(context1==context2);

    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

运行结果

true

证明两个获取方式是一样的

获取MIME类型

package cn.itcast.web.servletcontext;

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

public class Context1 extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        /**ServletContext对象获取
         * 1.通过request对象获取
         * request.getServletContext();
         * 2. 通过HttpServlet获取
         * this.getServletContext();
         */

//        //1. 通过request对象获取
//        ServletContext context1= request.getSession().getServletContext();
        //2. 通过HttpServlet获取
        ServletContext context = this.getServletContext();

        //3. 定义文件名称
        String filename="a.jpg";

        //4.获取MIME类型
        String mimeType = context.getMimeType(filename);
        System.out.println(mimeType);

    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

运行结果

image/jpeg

可以在web.xml中查看更多mime类型

域对象

context1

package cn.itcast.web.servletcontext;

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

public class Context1 extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        /**ServletContext对象获取
         * 1.通过request对象获取
         * request.getServletContext();
         * 2. 通过HttpServlet获取
         * this.getServletContext();
         */

//        //1. 通过request对象获取
//        ServletContext context1= request.getSession().getServletContext();
        //2. 通过HttpServlet获取
        ServletContext context = this.getServletContext();

        //设置数据
        context.setAttribute("msg","haha");

    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

context2

package cn.itcast.web.servletcontext;

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

public class Context2 extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        /**ServletContext对象获取
         * 1.通过request对象获取
         * request.getServletContext();
         * 2. 通过HttpServlet获取
         * this.getServletContext();
         */

//        //1. 通过request对象获取
//        ServletContext context1= request.getSession().getServletContext();
        //2. 通过HttpServlet获取
        ServletContext context = this.getServletContext();

        //获取数据
        Object msg = context.getAttribute("msg");
        System.out.println(msg);
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

我们并没有做任何的转发或者重定向的操作

只需要先访问context1设置键值对，再访问context2便会有了

也就是共享了所有用户的请求数据，这个对象很不安全，而且生命周期长，容易造成内存占用大和一系列安全问题

获取文件服务路径

• 方法：String getRealPath(String path);

分别在src,web,和WEB-INF下创建三个文件，分别为a.txt,b.txt,c.txt

以b.txt为例

package cn.itcast.web.servletcontext;

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

public class Context3 extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        /**ServletContext对象获取
         * 1.通过request对象获取
         * request.getServletContext();
         * 2. 通过HttpServlet获取
         * this.getServletContext();
         */

//        //通过request对象获取
//        ServletContext context1= request.getSession().getServletContext();
        //通过HttpServlet获取
        ServletContext context = this.getServletContext();

        //获取文件的服务器路径
        String realPath = context.getRealPath("/b.txt");
        System.out.println(realPath);
        File file=new File(realPath);
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

运行结果

F:\apache-tomcat-8.5.57-windows-x64\apache-tomcat-8.5.57\webapps\response\b.txt

c.txt只需要改为/WEB-INF/c.txt

a.txt比较麻烦，src下的所有东西都将放到WEB-INF下的classes,需要改为/WEB-INF/classes/a.txt

会话技术

1. 会话：一次会话中包含多次请求和响应

   • 一次会话：浏览器第一次给服务器资源发送请求，会话建立，直到有一方断开为止

2. 功能：在一次会话的范围内，共享数据

3. 方式：

   1. 客户端会话技术：Cookie

   2. 服务器端会话技术：Session

快速入门

• 使用步骤：

  1. 创建Cookie对象 new Cookie(String name,String value)

  2. 发送Cookie对象 response.addCookie(Cookie cookie)

  3. 获取Cookie对象，拿到数据 Cookie[] request.getCookies()

demo1创建并发送Cookie

package cn.itcast.cookie;

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

/**
 * Cookie快速入门
 */
public class demo1 extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.创建Cookie
        Cookie c=new Cookie("msg","hello");
        //2.发送Coookie
        response.addCookie(c);

    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

demo2获取Cookie

package cn.itcast.cookie;

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


public class demo2 extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //3.获取Cookie
        Cookie[] cs = request.getCookies();
        //遍历Cookie
        if(cs!=null){
            for (Cookie c : cs) {
                String name = c.getName();
                String value = c.getValue();
                System.out.println(name +" : "+ value);
            }
        }
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

先访问demo1，再放问demo2
运行结果

JSESSIONID : B0644875B54B93E70FF232624A6F4FA6
msg : hello
Phpstorm-d069594e : 0d583fa6-ad80-4735-a385-c10cee7ee32f

第一个和最后一个都是自带的，不用管，msg是获取到了