java实现简单验证码生成

// 
package app61;

import java.io.*;
import java.util.*;
import com.sun.image.codec.jpeg.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.awt.*;
import java.awt.image.*;

public class VerifyCode extends HttpServlet {

private Font mFont = new Font("Times New Roman", Font.PLAIN, 18); //设置字体

public void doGet(HttpServletRequest request, HttpServletResponse response) throws
ServletException, IOException {
//取得一个1000-9999的随机数
 HttpSession session = request.getSession(true);
 response.setContentType("image/gif");
 response.setHeader("Pragma", "No-cache");
 response.setHeader("Cache-Control", "no-cache");
 response.setDateHeader("Expires", 0);
 int width = 60, height = 20;

 ServletOutputStream out = response.getOutputStream();
 BufferedImage image = new BufferedImage(width, height,
 BufferedImage.TYPE_INT_RGB); //设置图片大小的
 Graphics gra = image.getGraphics();
 Random random = new Random();
 gra.setColor(getRandColor(200, 250)); //设置背景色rand垫底
 gra.fillRect(0, 0, width, height);
 gra.setColor(Color.black); //设置字体色
 gra.setFont(mFont);
 // 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到
 gra.setColor(getRandColor(160, 200));
 for (int i = 0; i < 155; i++) {
 int x = random.nextInt(width);
 int y = random.nextInt(height);
 int xl = random.nextInt(12);
 int yl = random.nextInt(12);
 gra.drawLine(x, y, x + xl, y + yl);
 }

 // 取随机产生的认证码(4位数字)
 String sRand = "";
 for (int i = 0; i < 4; i++) {
 String rand = String.valueOf(random.nextInt(10));
 sRand += rand;
 // 将认证码显示到图象中
 gra.setColor(new Color(20 + random.nextInt(110),
 20 + random.nextInt(110),
 20 + random.nextInt(110))); //调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
 gra.drawString(rand, 13 * i + 6, 16);
 }
 session.setAttribute("rand",sRand);
 // session.setAttribute("getImg", sRand);
 JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
 encoder.encode(image);
 out.close();
}

static Color getRandColor(int fc, int bc) { //给定范围获得随机颜色
 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);
}

 //Clean up resources
 public void destroy() {
 }
}