Response应用

常用方法：
重定向：sendRedirect(url)
设置响应头：setHeader()…
增加Cookie:addCookie();
国际化：setCharacterEncoding()–修改编码方式
输出数据：getWriter()–获取输出字符流，setContentType()设置文本类型
…

下载文件

package com.liu.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.FileInputStream;
import java.io.IOException;

public class FileServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取下载文件路径
        String realPath = "F:\\JavaWeb\\Javaweb-01\\response\\src\\main\\resources\\wallhaven-5we787.jpg";
        System.out.println("下载文件的路径为："+realPath);
        //下载的文件名是啥
        String fileName = realPath.substring(realPath.lastIndexOf("\\")+1);
        System.out.println("文件名称为"+fileName);
        //让浏览器支持下载文件
        resp.setHeader("Content-Disposition","attachment;filename="+fileName);
        //获取下载文件的输入流
        FileInputStream in = new FileInputStream(realPath);
        //创建缓冲区
        int len=0;
        byte[] buffer = new byte[1024];
        //获取outputstream对象
        ServletOutputStream outputStream = resp.getOutputStream();
        //将Fileoutputstram流写入缓冲区,使用outputstream将流输入从缓冲区写到客户端
        while((len=in.read(buffer))>0){
            outputStream.write(buffer,0,len);
        }
        //
        in.close();
        outputStream.close();
    }

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

验证码实现

package com.liu.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 ImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //让浏览器5秒刷新一次
        resp.setHeader("refresh", "3");

        //在内存中创建图片
        BufferedImage image = new BufferedImage(80, 20, BufferedImage.TYPE_INT_RGB);
        //得到图片
        Graphics2D graphics = (Graphics2D) image.getGraphics();//一支笔
        //设置图片的背景颜色
        graphics.setColor(Color.white);
        graphics.fillRect(0, 0, 80, 20);
        //给图片写数据
        graphics.setColor(Color.BLUE);
        graphics.setFont(new Font(null,Font.BOLD,20));
        graphics.drawString(makeNum(),0,20);

        //告诉浏览器，这个请求用图片方式打开
        resp.setContentType("image/jpeg");
        resp.setDateHeader("expires",-1);
        resp.setHeader("Cache-Control","no-cache");
        resp.setHeader("Pragma","no-cache");
        //图片写给浏览器
        ImageIO.write(image,"jpg",resp.getOutputStream());

    }

    //随机数
    private String makeNum() {
        Random random = new Random();
        String num = random.nextInt(22222222) + "";
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < 8 - num.length(); i++) {
            sb.append("0");

        }
        num = num + sb.toString();
        return num;

    }

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

重定向
web资源B收到一个客户端请求后，通知客户端去访问另一个web资源C

package com.liu.servlet;

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 RedirectServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.sendRedirect("/resp/down");
    }

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