JAVA验证码[含字母数字]

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.util.Random;
import javax.imageio.ImageIO;

import javax.servlet.*;
import java.io.*;
import javax.servlet.http.*;

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

public class RandomCode extends HttpServlet {

/**
* The doGet method of the servlet. <br>
*
* This method is called when a form. has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

this.doPost(request, response);
}

/**
* The doPost method of the servlet. <br>
*
* This method is called when a form. has its tag value method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

//  验证码图片的宽度。
int width = 70;
//验证码图片的高度。
int height = 36;
BufferedImage buffImg = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
Graphics2D g = buffImg.createGraphics();

//创建一个随机数生成器类。
Random random = new Random();

// 设定图像背景色(因为是做背景，所以偏淡)
g.setColor(getRandColor(180, 250));
g.fillRect(0, 0, width, height);
//创建字体，字体的大小应该根据图片的高度来定。
Font font = new Font("Times New Roman", Font.PLAIN, 28);
//设置字体。
g.setFont(font);

//画边框。
g.setColor(Color.BLACK);
g.drawRect(0, 0, width - 1, height - 1);
//  随机产生160条干扰线，使图象中的认证码不易被其它程序探测到。
g.setColor(Color.GRAY);
for (int i = 0; i < 50; i++) {
int x = random.nextInt(width);
int y = random.nextInt(height);
int xl = random.nextInt(12);
int yl = random.nextInt(12);
g.drawLine(x, y, x + xl, y + yl);
}

//randomCode用于保存随机产生的验证码，以便用户登录后进行验证。
StringBuffer randomCode = new StringBuffer();

// 设置默认生成4个验证码
int length = 4;
//   设置备选验证码:包括"a-z"和数字"0-9"
String base = "abcdefghijklmnopqrstuvwxyz0123456789";

int size = base.length();

//随机产生4位数字的验证码。
for (int i = 0; i < length; i++) {
//得到随机产生的验证码数字。
int start = random.nextInt(size);
String strRand = base.substring(start, start + 1);

//用随机产生的颜色将验证码绘制到图像中。
//   g.setColor(new Color(red,green,blue));
// 生成随机颜色(因为是做前景，所以偏深)
g.setColor(getRandColor(1, 100));
g.drawString(strRand, 13 * i + 6, 28);

//将产生的四个随机数组合在一起。
randomCode.append(strRand);
}
//将四位数字的验证码保存到Session中。
HttpSession session = request.getSession();
session.setAttribute("rand", randomCode.toString());

//禁止图像缓存。
response.setHeader("Pragma", "no-cache");
response.setHeader("Cache-Control", "no-cache");
response.setDateHeader("Expires", 0);

response.setContentType("image/jpeg");

//将图像输出到Servlet输出流中。
ServletOutputStream sos = response.getOutputStream();
ImageIO.write(buffImg, "jpeg", sos);
sos.close();

}

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);
}

}