Response

常见的HTTP协议响应头有哪些？

Location: 服务器通过这个头，来告诉浏览器跳到哪里
Server：服务器通过这个头，告诉浏览器服务器的型号
Content-Encoding：服务器通过这个头，告诉浏览器，数据的压缩格式
Content-Length: 服务器通过这个头，告诉浏览器回送数据的长度
Content-Language: 服务器通过这个头，告诉浏览器语言环境
Content-Type：服务器通过这个头，告诉浏览器回送数据的类型
Refresh：服务器通过这个头，告诉浏览器定时刷新
Content-Disposition: 服务器通过这个头，告诉浏览器以下载方式打数据
Transfer-Encoding：服务器通过这个头，告诉浏览器数据是以分块方式回送的
Expires: -1  控制浏览器不要缓存
Cache-Control: no-cache  
Pragma: no-cache   

Htt状态码

 

文件下载请求头

  resp.setHeader("Content-Disposition",
                "attachment;filename="+URLEncoder.encode(fileName,"utf-8"));

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.*;
import java.net.URLEncoder;

public class ResponseDownload extends HttpServlet {

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

        String realPath = this.getServletContext().getRealPath("/WEB-INF/classes/网报.png");
        String fileName = realPath.substring(realPath.lastIndexOf("/") + 1);
        resp.setHeader("Content-Disposition",
                "attachment;filename="+URLEncoder.encode(fileName,"utf-8"));

        FileInputStream in = new FileInputStream(realPath);
        ServletOutputStream out = resp.getOutputStream();
        byte[] buffer = new byte[1024];
        int len = 0;
        while ( (len = in.read(buffer)) != -1){
            out.write(buffer,0,len);
        }
        out.close();
        in.close();
    }

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

 生成验证码

public class ResponseImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //如何让浏览器三秒自动刷新一次
        resp.setHeader("refresh", "3");
        //在内存中创建一个图片
        BufferedImage bufferedImage = new BufferedImage(80, 20, BufferedImage.TYPE_INT_RGB);
        //得到图片
        Graphics2D bi = (Graphics2D) bufferedImage.getGraphics();
        //设置背景颜色为白色
        bi.setColor(Color.WHITE);
        bi.fillRect(0, 0, 80, 20);
        //给图片写数据
        bi.setColor(Color.BLUE);
        bi.setFont(new Font(null, Font.BOLD, 20));
        bi.drawString(makeNum(), 0, 20);
        //告诉浏览器用图片的方式打开
        resp.setContentType("image/jpeg");
        //网站存在缓存，不让浏览器缓存
        resp.setDateHeader("Expires",0);
        resp.addHeader("Cache-Control","no-cache");
        resp.setHeader("Pragma","no-cache");
        ImageIO.write(bufferedImage, "jpeg", resp.getOutputStream());

    }

    private String makeNum() {
        Random random = new Random();
        String num = random.nextInt(9999999) + "";
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < 7 - num.length(); i++) {
            sb.append("0");
        }
        return sb.toString() + num;
    }

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

 重定向

public class ResponseRedirectServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String contextPath = this.getServletContext().getContextPath();
        resp.sendRedirect(contextPath+"/responseImageServlet"); //重定向
        //相当于
        //resp.setHeader("Location", contextPath+"/responseImageServlet");
        //resp.setStatus(302);
    }
}