servlet页面生成验证码

验证码：

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.awt.*;
import java.awt.image.*;
import javax.imageio.ImageIO;
public class CheckServlet extends HttpServlet
{
private static int WIDTH = 60; //验证码图片宽度
private static int HEIGHT = 20; //验证码图片高度
public void doGet(HttpServletRequest request,HttpServletResponse response)
throws ServletException,IOException
{
HttpSession session = request.getSession();
response.setContentType("image/jpeg");
ServletOutputStream sos = response.getOutputStream();
//设置浏览器不要缓存此图片
response.setHeader("Pragma","No-cache");
response.setHeader("Cache-Control","no-cache");
response.setDateHeader("Expires", 0);
//创建内存图象并获得其图形上下文
BufferedImage image =
new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
Graphics g = image.getGraphics();
//产生随机的认证码
char [] rands = generateCheckCode();
//产生图像
drawBackground(g);
drawRands(g,rands);
//结束图像的绘制过程，完成图像
g.dispose();
//将图像输出到客户端
ByteArrayOutputStream bos = new ByteArrayOutputStream();
ImageIO.write(image, "JPEG", bos);
byte [] buf = bos.toByteArray();
response.setContentLength(buf.length);
//下面的语句也可写成：bos.writeTo(sos);
sos.write(buf);
bos.close();
sos.close();
//将当前验证码存入到Session中
session.setAttribute("check_code",new String(rands));
//直接使用下面的代码将有问题，Session对象必须在提交响应前获得
//request.getSession().setAttribute("check_code",new String(rands));
}
//生成一个4字符的验证码
private char [] generateCheckCode()
{
//定义验证码的字符表
String chars = "0123456789abcdefghijklmnopqrstuvwxyz";
char [] rands = new char[4];
for(int i=0; i<4; i++)
{
int rand = (int)(Math.random() * 36);
rands[i] = chars.charAt(rand);
}
return rands;
}
private void drawRands(Graphics g , char [] rands)
{
g.setColor(Color.BLACK);
g.setFont(new Font(null,Font.ITALIC|Font.BOLD,18));
//在不同的高度上输出验证码的每个字符
g.drawString("" + rands[0],1,17);
g.drawString("" + rands[1],16,15);
g.drawString("" + rands[2],31,18);
g.drawString("" + rands[3],46,16);
System.out.println(rands);
}
private void drawBackground(Graphics g)
{
//画背景
g.setColor(new Color(0xDCDCDC));
g.fillRect(0, 0, WIDTH, HEIGHT);
//随机产生120个干扰点
for(int i=0; i<120; i++)
{
int x = (int)(Math.random() * WIDTH);
int y = (int)(Math.random() * HEIGHT);
int red = (int)(Math.random() * 255);
int green = (int)(Math.random() * 255);
int blue = (int)(Math.random() * 255);
g.setColor(new Color(red,green,blue));
g.drawOval(x,y,1,0);
}
}
}