JAVA验证码功能实现（生成验证码的Servlet）

package com.lovo.web.servlet;

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

import javax.servlet.ServletException;
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;


/**
 * Copyright (C), 2006-2011, ChengDu Lovo info. Co., Ltd.
 * FileName: Test.java
 * 生成验证码的Servlet
 * 
 * @author  何天玺
 * @Date    2014年6月19日
 * @version 1.00 
 */
public class RadomCodeServlet extends HttpServlet{
	public void doGet(HttpServletRequest req,HttpServletResponse resp)throws ServletException,IOException{
		int width = 90;
		int height = 40;
		//创建画板
		BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_BGR);
		//获取画笔
		Graphics g = image.getGraphics();
		//绘制一个白色背景
		g.setColor(Color.white);
		g.fillRect(0, 0, width, height);
		//随机出现的字符
		String allStr = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
		char [] cs = allStr.toCharArray();
		//随机生成5-10条线
		for(int i = 0;i<generateCode(6)+5;i++){
			//随机产生画笔的颜色
			g.setColor(new Color(generateCode(256),generateCode(256),generateCode(256)));
			//画随机线条
			g.drawLine(generateCode(width), generateCode(height),generateCode(width), generateCode(height));			
		}
		for(int i = 0;i < 4;i++){
			String code = cs[generateCode(cs.length)]+"";
			//随机产生画笔的颜色
			g.setColor(new Color(generateCode(256),generateCode(256),generateCode(256)));
			//随机设置字体大小
			g.setFont(new Font("黑体", generateCode(3),generateCode(11)+15));
			
			g.drawString(code, i*10+generateCode(11),generateCode(11)+25);	
		}
		//将图片进行编码后输出到页面上
		JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(resp.getOutputStream());
		encoder.encode(image);
	}
	/**
	 * 产生随机数 
	 * @param num
	 * @return
	 */
	public int generateCode(int num){
		return (int)(Math.random() * num);
	}
}