产生验证码图像

//产生验证码图像GenerateJPEGServlet.java

package my.bbs.servlets;

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

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class GenerateJPEGServlet extends HttpServlet {

private static int WIDTH = 120;
private static int HEIGHT = 43;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO 自动生成方法存根
HttpSession session = request.getSession();
response.setContentType("image/jpeg");
ServletOutputStream sos = response.getOutputStream();

//设置浏览器不缓存此图片
response.setHeader("Pragma", "No-cache");
response.setHeader("Cache-Control", "No-cache");
response.setDateHeader("Expires", 0);

//创建内存图像并获得其图形上下文
BufferedImage image = new BufferedImage(WIDTH,HEIGHT,BufferedImage.TYPE_INT_RGB);
Graphics g = image.getGraphics();

//产生随机的验证码
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);
//下面的语句也可以写成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));



}

private char[] generateCheckCode()
{
//定义验证码存的字符表
String chars ="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
char [] rands = new char[6];
for(int i=0;i<6;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],4,25);
g.drawString(""+rands[1], 20, 35);
g.drawString(""+rands[2],43,30);
g.drawString(""+rands[3],60,35);
g.drawString(""+rands[4],80,29);
g.drawString(""+rands[5],102,33);
}

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, 2, 1);
}
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO 自动生成方法存根
doGet(request,response);
}

}