生成一个验证码

package response_test;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import cn.dsna.util.images.ValidateCode;

public class Response_demo4 extends HttpServlet {

	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		//test(response);
		//告诉客户端不要使用缓存
		response.setHeader("pragma", "no-cache");
		response.setHeader("cache-control", "no-cache");
		response.setIntHeader("expores", 0);
		//使用ValidateCode.jar
		ValidateCode vc=new ValidateCode(110, 25, 4, 9);
		String code=vc.getCode();
		System.out.println(code);//测试
		vc.write(response.getOutputStream());
	}

	private void test(HttpServletResponse response) throws IOException {
		//告诉客户端不要使用缓存
		response.setHeader("pragma", "no-cache");
		response.setHeader("cache-control", "no-cache");
		response.setIntHeader("expores", 0);
		
		int width=110;
		int height=25;
		
		//在内存中创建一个图像对象
		BufferedImage img =new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
		
		//创建一个画笔
		Graphics g=img.getGraphics();
		
		//给图片添加背景色
		g.setColor(Color.PINK);
		g.fillRect(1, 1, width-2, height-2);
		
		//设置文本样式
		g.setColor(Color.BLUE);
		g.setFont(new Font("宋体", Font.BOLD|Font.ITALIC, 15));
		
		//给图片添加文本
		Random rand=new Random();
		int position=20;
		for(int i=0;i<4;i++){
			g.drawString(rand.nextInt(10)+"", position, 20);
			position+=20;
		}
		
		
		for (int i = 0; i < 6; i++) {
			g.drawLine(rand.nextInt(width), rand.nextInt(height), rand.nextInt(width), rand.nextInt(height));
		}
		ImageIO.write(img, "jpg", response.getOutputStream());
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

	}

}

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>登陆界面</title>
</head>
<script>
	function changeCode(){
		var img=document.getElementsByTagName("img")[0];
		img.src="/response_test/demo4?time="+new Date().getTime();
	}
</script>
<body>
	<form action="#" method="post">
		用户名： <input type="text" name="" id="" style="width: 139px; "><br>
		密码：   <input type="text" name="" id=""> <br>
		验证码：<input type="text" name=""><img src="/response_test/demo4" alt="" onclick="changeCode()"><br>
		<input type="submit" name="" id="">
	</form>
</body>
</html>

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