验证码实现

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生成图片的类

package com.randy.util;

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

public class IdentityImage {

	private static final char[] CHARS = new char[] { '2', '3', '4', '5', '6',
			'7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'J', 'K',
			'L', 'M', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z' };

	private static Random random = new Random();

	public static String getRandomString(int num) {
		StringBuffer buffer = new StringBuffer();
		for (int i = 0; i < num; i++) {
			buffer.append(CHARS[random.nextInt(CHARS.length)]);
		}
		return buffer.toString();
	}

	private static Color getRandomColor() {
		return new Color(random.nextInt(255), random.nextInt(255),
				random.nextInt(255));
	}

	private static Color getReverseColor(Color c) {
		return new Color(fixRGB(255 - random.nextInt(c.getRed())),
				fixRGB(255 - random.nextInt(c.getGreen())), fixRGB(255 - random.nextInt(c
						.getBlue())));
	}
	
	private static int fixRGB(int i) {
		if(i > 0) {
			return i;
		}
		return 1;
	}
	
	public static BufferedImage createImage(String string,int width,int height,int x, int y,int numHSBNoise) {
		BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
		Graphics2D g = image.createGraphics();
		Color c = getRandomColor();
		g.setColor(c);
		g.fillRect(0, 0, width, height);
		g.setColor(getReverseColor(c));
		g.setFont(new Font(Font.SANS_SERIF,Font.BOLD,16));
		g.drawString(string, x, y);
		for(int i = 0; i < numHSBNoise; i++) {
			g.fillRect(random.nextInt(width), random.nextInt(height), 1, 1);
		}
		return image;
	}

}

验证码的servlet

package servlets;

import java.awt.image.BufferedImage;
import java.io.IOException;

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;

import com.randy.util.IdentityImage;
import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;

/**
 * Servlet implementation class IdentityImageServlet
 */
public class IdentityImageServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

	/**
	 * @see HttpServlet#HttpServlet()
	 */
	public IdentityImageServlet() {
		super();
	}

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	protected void doGet(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		HttpSession session = request.getSession(true);
		String randomString = IdentityImage.getRandomString(5);
		session.setAttribute("randomString", randomString);
		BufferedImage image = IdentityImage.createImage(randomString, 100, 30, 18, 20, 100);
		ServletOutputStream outputStream = response.getOutputStream();
		JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(outputStream);
		encoder.encode(image);
		outputStream.flush();
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	protected void doPost(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
	}

}

使用：

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Identity Image</title>
<script type="text/javascript">
function reloadImage() {
	document.getElementById("btn").disabled = true;
	document.getElementById("identity").src = 'servlets/IdentityImageServlet?ts=' + new Date().getTime();
}
</script>
</head>
<body>
<img src="servlets/IdentityImageServlet" id="identity" onload="btn.disabled=false;" />
<input type="button" value="change" onclick="reloadImage()" id="btn">
</body>
</html>

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