Servlet 输出图片验证码

package com.qad.jpg;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

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

import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;

public class IdentityServlet extends HttpServlet{
//不包含'0','o','i','1'等不容易辨认的字符
public static final char[] chars={'2','3','4','5','6','7','8','9'
,'A','B','C','D','E','F','G','H','J','K','L','M','N'
,'P','Q','R','S','T','U','V','W','X','Y','Z'};
//生成随机数
public static Random random = new Random();
//获取随机数
public static String getRandomString(){
//字符串缓存
StringBuffer buffer = new StringBuffer();
//循环六次,每次随机取一个字符
for(int i = 0;i < 6; i++){
buffer.append(chars[random.nextInt(chars.length)]);
}
return buffer.toString();
}
//获取随机的颜色
public static Color getRandomColor(){
return new Color(random.nextInt(255),random.nextInt(255)
,random.nextInt(255));
}
//返回某颜色的反色
public static Color getReverseColor(Color c){
return new Color(255-c.getRed(),255-c.getGreen(),255-c.getBlue());
}
//GET方法
public void doGet(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException{
//设置输出类型为jpeg格式
response.setContentType("image/jpeg");
//获取随机字符串
String randomString = getRandomString();
//将获取的随机字符串放到session中
request.getSession(true).setAttribute("randomString", randomString);
int width = 100;//设置图片宽度
int height = 30;//设置图片高度
//获取随机颜色,用于背景色
Color color = getRandomColor();
//获取反色,用于前景色
Color reverse = getReverseColor(color);
//创建一个彩色图片
BufferedImage bi = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
Graphics2D g = bi.createGraphics();//获取绘图对象
g.setFont(new Font(Font.SANS_SERIF,Font.BOLD,16));//设置字体
g.setColor(color);//设置颜色
g.fillRect(0, 0, width, height);//绘制背景
g.setColor(reverse);//设置颜色
g.drawString(randomString, 18, 20);//绘制随机字符
//画噪点,最多100个
for (int i = 0,n=random.nextInt(100);i<n;i++){
g.drawRect(random.nextInt(width),random.nextInt(height), 1, 1);//随机噪音点
}
ServletOutputStream out = response.getOutputStream();
//转成jpeg格式
JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
encoder.encode(bi);
out.flush();
}

}