Response验证码

验证码功能

1. 前端实现：js
2. 后端实现：Java的image（图片类），生成一个图片，响应到前端。

StringBuffer缓存区设置

append方法返回StringBuffer类的实例化类对象。

public class StringBufferDemo01{public static void main(String args[]){StringBuffer buf = new StringBuffer() ;	// 声明StringBuffer对象 buf.append("Hello ") ;					// 向StringBuffer中添加内容buf.append("World").append("!!!") ;		// 可以连续调用append()方法buf.append("\n") ;						// 添加一个转义字符buf.append("数字 = ").append(1).append("\n") ;	// 添加数字buf.append("字符 = ").append('C').append("\n");	 // 添加字符buf.append("布尔 = ").append(true) ;	// 添加布尔值System.out.println(buf) ;			// 直接输出对象，调用toString()}
};

代码

package com.xin.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 {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//浏览器五秒自动刷新resp.setHeader("refresh","5");//在内存中创建一个图片BufferedImage image = new BufferedImage(80, 20,BufferedImage.TYPE_3BYTE_BGR);//得到一支2d的笔Graphics2D graphics =(Graphics2D) image.getGraphics();//设置背景颜色graphics.setColor(Color.yellow);//设置形状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，这个请求用图片的方式打开resp.setContentType("image/png");// resp.setContentType("image/jpeg");//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, "png",resp.getOutputStream());}//生成随机数private String makeNum(){Random random = new Random();String s = random.nextInt(99999) + "";StringBuffer sf = new StringBuffer();for (int i=0;i<5-s.length();i++){sf.append("0");}s = sf.toString() + s;return s;}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req,resp);}
}