登陆时验证码的生成的代码

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
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;

/**
* Servlet implementation class CheckcodeServlet
*/
public class CheckcodeServlet extends HttpServlet {

private static final long serialVersionUID = 3776895994055269476L;
private int width = 60; // 图片宽度
private int height = 24; // 图片高度
private int count = 4; // 码数

// 验证码源
private char[] codes = { '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', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' };

public CheckcodeServlet() {
super();
// TODO Auto-generated constructor stub
}

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
* response)
*/
protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
this.doPost(request, response);
}

/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
* response)
*/
protected void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
BufferedImage bi = new BufferedImage(width, height,
BufferedImage.TYPE_INT_RGB);
Graphics2D g = bi.createGraphics();

g.setColor(Color.WHITE);
g.fillRect(0, 0, width, height);// 画背景

g.setColor(Color.BLACK);
g.drawRect(0, 0, width - 1, height - 1);// 画边框

// 设置画笔的颜色和字体
g.setFont(new Font("Fixedsys", Font.PLAIN, 14));

StringBuilder sb = new StringBuilder();// 用来保存产生的码值
Random random = new Random();
for (int i = 0; i < count; i++) {
char c = codes[random.nextInt(codes.length)];
sb.append(c);
// 产生随机颜色
g.setColor(new Color(random.nextInt(256), random.nextInt(256),
random.nextInt(256)));
g
.drawString(String.valueOf(c), i * (width / count) + 2,
height - 7);
}
for (int i = 0; i < count; i++) {
// 产生随机颜色
g.setColor(new Color(random.nextInt(256), random.nextInt(256),
random.nextInt(256)));
g.drawLine(0, (height / 2), (width / count) + 62, height - 7);
g.drawLine((width / 2), 0, (width / count) + 62, height - 7);
}

// 把产生的验证码值保存到当前会话中
request.getSession().setAttribute("checkCode", sb.toString());

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

OutputStream os = response.getOutputStream();
ImageIO.write(bi, "jpeg", os); // 把内存图片写到客户端输出流
os.close();
}

}