HttpServletResponse

 

1、command键+鼠标左键查看HttpServletResponse的源码，然后再查看它继承的类ServletResponse的源码

 负责向浏览器发送数据的方法：

ServletOutputStream getOutputStream() throws IOException;

PrintWriter getWriter() throws IOException;

负责向浏览器发送响应头的方法：

  void setCharacterEncoding(String var1);

  void setContentLength(int var1);

  void setContentLengthLong(long var1);

  void setContentType(String var1);
  void setDateHeader(String var1, long var2);

  void addDateHeader(String var1, long var2);

  void setHeader(String var1, String var2);

  void addHeader(String var1, String var2);

  void setIntHeader(String var1, int var2);

  void addIntHeader(String var1, int var2);

 

可以在HttpServletResponse中查看到一些常量，响应的状态码，常见的有200、300、405、500、502等

2、常见应用

（1）向浏览器输出消息

 （2）下载文件

获取下载的路径

下载的文件名是啥

设置想办法让浏览器能够支持下载我们需要的东西

获取下载文件的输入流

创建缓冲区

获取OutputStream对象

将FileOutoutstream流写入到buffer缓冲区

使用OutputStream将缓冲区中的数据输出到客户端

 

 

新建一个response工程，按照之前的套路部署好文件、tomcat等

然后放置一张图片在resourese目录下，

 

 Fileservlet中的代码：

package com.liyu.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 {
            //        获取下载的路径
        String realPath = "/Users/dailingyi/IdeaProjects/javaweb-02-servlet1/response/target/classes/1.png";
        System.out.println("下载的文件路径："+realPath);
//                下载的文件名是啥
        String filename = realPath.substring(realPath.lastIndexOf("\\") + 1);
//        设置想办法让浏览器能够支持Content-Disposition下载我们需要的东西,如果是中文文件名还需要用URLEncoder.encode编码，否则有可能乱码
        resp.setHeader("Content-Disposition","attachment;filemame="+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 out = resp.getOutputStream();
//        将FileOutoutstream流写入到buffer缓冲区, 使用OutputStream将缓冲区中的数据输出到客户端
        while ((len = in.read(buffer))>0){
            out.write(buffer,0,len);
        }
        in.close();
        out.close();

    }

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

然后在web.xml中配置，运行即可在网页下载1.png图片

 （3）验证码功能

前端实现

后端实现，需要用到java的图片类，生成一个图片

ImageServlet java类

package com.liyu.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.BufferedInputStream;
import java.io.IOException;
import java.util.Random;

public class ImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //如何让浏览器5秒自动刷新一次
        resp.setHeader("refresh","3");
        
        //在内存中创建一个图片
        BufferedImage image = new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB);
        
        //得到图片
        Graphics2D g =(Graphics2D) image.getGraphics(); //笔
        //设置图片的背景颜色
        g.setColor(Color.white);
        g.fillRect(0,0,80,20);
        //给图片写数据
        g.setColor(Color.BLUE);
        g.setFont(new Font(null,Font.BOLD,20));
        g.drawString(makeNum(),0,20);

        //告诉浏览器，这个请求用图片的方式打开
        resp.setContentType("Image/jpg");
        //网站存在缓存，不让浏览器缓存
        resp.setDateHeader("expires",-1);
        resp.setHeader("Cache-Control","no-cache");
        resp.setHeader("Pragma","no-cache");

        //把图片写给浏览器
        boolean write = ImageIO.write(image,"jpg",resp.getOutputStream());

    }

    //生成随机数
    private String makeNum(){
        Random random = new Random();
        String num = random.nextInt(9999999) + "";
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i<7-num.length();i++){
            sb.append("0");
        }
        num = sb.toString()+num;
        return num;
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        
    }
}

然后在web.xml注册，运行测试

 

 出现验证码，且3秒更新一次

（4）实现重定向

 

一个web资源收到客户端请求后，它会通知客户端去访问另外一个web资源，这个过程叫重定向

常见场景：用户登录

void sendRedirect(String var1) throws IOException;

新建一个RedirectServlet，

package com.liyu.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("/response_war/img"); //重定向
    }

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

然后在web.xml注册

运行测试，访问http://localhost:8080/response_war/red会自动跳转到http://localhost:8080/response_war/img