JAVA Servlet实现验证码

package com.tenlee.servlet;

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;

/**
 * Servlet implementation class IdentityServlet
 */
public class IdentityServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
     
	public static final char[] CHARS = {'2', '3', '4', '5', '6', '7', '8', '9',
		'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'k', 'J', 'L', 'M', 'N'};
	public static Random random = new Random();
	
	public static String getRandomString() {
		StringBuffer buffer = new StringBuffer();
		for (int i = 0; i < 6; i++) {
			buffer.append(CHARS[random.nextInt(CHARS.length)]);
		}
		return buffer.toString();
	}
	
	public static Color getRandomColor() { //获取随机颜色
		return new Color(random.nextInt(255), random.nextInt(255),
				random.nextInt(255));
	}
	
	public static Color getReverseColor(Color c) { //返回某颜色反色
		return new Color(255- c.getRed(), 255 - c.getGreen(),
				255 - c.getBlue());
	}
	
    public IdentityServlet() {
        super();
    }

	protected void doGet(HttpServletRequest request, HttpServletResponse response) 
			throws ServletException, IOException {
		response.setContentType("image/jpeg"); //设置输出类型
		
		String randomString = getRandomString();//随机字符串
		request.getSession(true).setAttribute("randomString", randomString);
		
		int width = 100;
		int height = 30; //图片宽度和高度
		
		Color color = getRandomColor(); //获取随机颜色，用于背景色
		Color reverse = getReverseColor(color);// 反色，用于钱前景色
		
		BufferedImage bi = new BufferedImage(width, height,
				BufferedImage.TYPE_INT_RGB); //常见一个彩色图片
		Graphics2D g = bi.createGraphics(); //获取绘制对象
		g.setFont(new Font(Font.SANS_SERIF, Font.BOLD, 16)); //设置字体
		g.setColor(color);//设置字体颜色
		g.fillRect(0, 0, width, height);//绘制背景
		g.setColor(reverse);//设置颜色
		g.drawString(randomString, 18, 20);
		for(int i = 0, n = random.nextInt(100); i < n; i++) {//画最多100个噪点
			g.drawRect(random.nextInt(width), random.nextInt(height), 
					1, 1);//随机噪音点
		}
		ServletOutputStream out = response.getOutputStream(); //转换成jpeg格式
		JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);//编码器
		encoder.encode(bi); //对图片进行编码
		out.flush();//清除缓存，即输出到客户端
		
	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		
	}

}