ValidateCode.java

package net.loyin.util;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.util.Random;

import javax.imageio.ImageIO;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpSession;

/**
 * 随机生成四位验证码,并输出图像
 */
@SuppressWarnings("serial")
public class ValidateCode extends HttpServlet {
	private static final int WIDTH = 150;
	private static final int HEIGHT = 50;
	private static final String chars = "23456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghjkmnpqrstuvwxyz";
	@Override
	public void service(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setContentType("image/jpeg");

		// 防止浏览器缓冲
		response.setHeader("Pragma", "No-cache");
		response.setHeader("Cache-Control", "no-cache");
		response.setDateHeader("Expires", 0);
		HttpSession session = request.getSession();
		BufferedImage image = new BufferedImage(WIDTH, HEIGHT,BufferedImage.TYPE_INT_RGB);
		Graphics g = image.getGraphics();
		char[] rands = getCode(4);
		drawBackground(g);
		drawRands(g, rands);
		g.dispose();
		ServletOutputStream out = response.getOutputStream();
		ByteArrayOutputStream bos = new ByteArrayOutputStream();
		ImageIO.write(image, "PNG", bos);
		byte[] buf = bos.toByteArray();
		response.setContentLength(buf.length);
		out.write(buf);
		bos.close();
		out.close();
		session.setAttribute("check", new String(rands).toLowerCase());
	}

	/**
	 * 产生随机数
	 * 
	 * @return
	 */
	private char[] getCode(int length) {
		char[] rands = new char[length];
		for (int i = 0; i < length; i++) {
			int rand = (int) (Math.random() * chars.length());
			rands[i] = chars.charAt(rand);
		}
		return rands;
	}

	/**
	 * 绘制背景
	 * 
	 * @param g
	 */
	private void drawBackground(Graphics g) {
		g.setColor(new Color(0xDCeeee));
		g.fillRect(0, 0, WIDTH, HEIGHT);
		Random random=new Random();
		int len=0;
		while(len<=5){
			len=random.nextInt(15);
		}
		for (int i = 0; i < len; i++) {
			int x = (int) (random.nextInt(WIDTH));
			int y = (int) (random.nextInt(HEIGHT) );
			int red = (int) (255-random.nextInt(200));
			int green = (int) (255-random.nextInt(200) );
			int blue = (int) (255-random.nextInt(200) );
			g.setColor(new Color(red, green, blue));
//			g.drawLine(x, y, random.nextInt(WIDTH)-x, random.nextInt(HEIGHT)-y);
			g.drawOval(x, y, 2, 2);
		}
	}
	/**
	 * 绘制验证码
	 * 
	 * @param g
	 * @param rands
	 */
	private void drawRands(Graphics g, char[] rands) {
		Random random=new Random();
		
		g.setFont(new Font("黑体", Font.ITALIC | Font.BOLD, 45));
		for(int i=0;i<rands.length;i++){
			int red = (int) (random.nextInt(255));
			int green = (int) (random.nextInt(255) );
			int blue = (int) (random.nextInt(255) );
			g.setColor(new Color(red, green, blue));
			g.drawString("" + rands[i], i*40, 40);
		}
	}
	@Override
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		service(request, response);
	}
}