java实现验证码功能

package com.verification_code.servlet;

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

public class ImgServlet extends HttpServlet{

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        // TODO Auto-generated method stub
        doPost(req,resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        
        // TODO Auto-generated method stub
        //设置响应开头
        resp.setContentType("image/jpeg");
        //设置页面不缓存
        resp.setHeader("pragma", "no-cache");
        resp.setHeader("cache-control", "no-cache");
        resp.setDateHeader("expires", 0);
        OutputStream out = resp.getOutputStream();
        //设置图片的宽高
        int width=88,height=20;
        BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
        Graphics g = image.getGraphics();
        //生成随机类
        Random random = new Random();
        g.setColor(Color.WHITE);
        g.fillRect(0, 0, width, height);
        //设置字体
        g.setFont(new Font("Times New Roman",Font.BOLD+Font.ITALIC,18));
        // 画边框
        g.setColor(getRandColor(0, 20)); // ---2
        g.drawRect(0, 0, width - 1, height - 1);
        // 随机产生干扰线
        int count = 100;
        int lineWidth = 3; // 干扰线的宽度
        for (int i = 0; i < count; i++) {
            g.setColor(getRandColor(150, 200)); // ---3
            int x = random.nextInt(width - lineWidth - 1) + 1; // 保证画在边框之内
            int y = random.nextInt(height - lineWidth - 1) + 1;
            int xl = random.nextInt(lineWidth);
            int yl = random.nextInt(lineWidth);
            g.drawLine(x, y, x + xl, y + yl);
        }
        //生成随机验证码
        String sRand="";
        String str[]={"0","1","2","3","4","5","6","7","8","9",
                "A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"};
        for(int i=0;i<4;i++){
            int rand = random.nextInt(36);
            sRand+=str[rand];
            //设置随机颜色
            g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));
            //绘制
            g.drawString(str[rand], 20*i+8, 16);
        }
        req.getSession().setAttribute("Verification_code",sRand);
        g.dispose();
        ImageIO.write(image, "JPEG", out);
    }
    public Color getRandColor(int fc, int bc) { // 取得给定范围随机颜色
        Random random = new Random();
        if (fc > 255) {
            fc = 255;
        }
        if (bc > 255) {
            bc = 255;
        }
        int r = fc + random.nextInt(bc - fc);
        int g = fc + random.nextInt(bc - fc);
        int b = fc + random.nextInt(bc - fc);
        return new Color(r, g, b);
    }

}

<img id="id_code" name="code" src="image" title="看不清，换一张" onclick="refresh()" style="display: inline;">


<script type="text/javascript">
    function refresh(){
        document.getElementById("id_code").src="image?"+Math.random();
        //loginForm.code.src="image?"+Math.random();
    }
</script>