Java web 开发： 随机生成验证码，支持大小写字母、数字；随机字体

java随机产生验证码，可以随机生成数字、大写字母、小写字母。还可以随机生成文字字体、及大小。在图片上面可能字体都不不同、大小不等。

package com.hoo.util;


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

import javax.imageio.ImageIO;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
 * <b>function:</b> 验证码生成工具类
 * @project NetWorkService
 * @package com.hoo.util 
 * @fileName ValidCodeUtils.java
 * @createDate 2010-8-3 下午03:05:50
 * @author hoojo
 */
@SuppressWarnings("unused")
public class ValidCodeUtils {
	/*********************************************************************
	 * 验证码宽度
	 */
	public static int WIDTH = 60;
	/***
	 * 验证码高度
	 */
	public static int HEIGHT = 20;
	
	/**********************************************************************
	 * 验证码背景颜色COLOR_FC_BG 应当小于COLOR_BC_BG
	 */
	public static int COLOR_FC_BG = 200;
	/***
	 * 验证码背景颜色COLOR_FC_BG 应当小于COLOR_BC_BG
	 */
	public static int COLOR_BC_BG = 250;
	
	/**********************************************************************
	 * 验证码背景干扰线颜色COLOR_FC_LINE 应当小于COLOR_BC_LINE
	 */
	public static int COLOR_FC_LINE = 160;
	/***
	 * 验证码背景干扰线颜色COLOR_FC_LINE 应当小于COLOR_BC_LINE
	 */
	public static int COLOR_BC_LINE = 200;
	
	/***************************************************************************
	 * 验证码颜色COLOR_FC_CODE 应当小于COLOR_BC_CODE
	 */
	public static int COLOR_FC_CODE = 20;
	/***
	 * 验证码颜色COLOR_FC_CODE 应当小于COLOR_BC_CODE
	 */
	public static int COLOR_BC_CODE = 170;
	
	/***************************************************************************
	 * 生成在指定范围内的颜色
	 * @param fc 范围fc color值 小于255
	 * @param bc 范围bc color值 小于255
	 * @return Color
	 */
	private static Color getRandColor(int fc, int bc) {
		Random random = new Random();
		if (fc < 0)
			fc = 0;
		if (bc < 0)
			bc = 1;
		if (fc > 255)
			fc = 255;
		if (bc > 255)
			bc = 255;
		if (bc == fc) 
			bc += 10;
		int temp = 0;
		if (bc < fc) {
			temp = bc;
			bc = fc;
			fc = temp;
		}
		int r = fc + random.nextInt(bc - fc);
		int g = fc + random.nextInt(bc - fc);
		int b = fc + random.nextInt(bc - fc);
		return new Color(r, g, b);
	}

	/**
	 * <b>function:</b> 生成图片方法
	 * @createDate 2010-8-3 下午03:06:22
	 * @author hoojo
	 * @param request HttpServletRequest
	 * @param response HttpServletResponse
	 * @return boolean
	 * @throws Exception
	 */
	public static boolean getImage(HttpServletRequest request, HttpServletResponse response) throws Exception{
		response.reset();
		response.setContentType("image/jpeg");
		// 设置页面不缓存
		response.setHeader("Pragma", "No-cache");
		response.setHeader("Cache-Control", "no-cache");
		response.setDateHeader("Expires", 0);
		// 在内存中创建图象		
		BufferedImage image = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);

		// 获取图形上下文
		Graphics img = image.getGraphics();
		// 生成随机类
		Random random = new Random();

		// 设定背景色
		img.setColor(getRandColor(COLOR_FC_BG, COLOR_BC_BG));
		img.fillRect(0, 0, WIDTH, HEIGHT);

		// 设定字体
		img.setFont(new Font("Times New Roman", Font.PLAIN, 18));

		// 画边框
		// g.setColor(new Color());
		// g.drawRect(0,0,width-1,height-1);

		// 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到
		img.setColor(getRandColor(COLOR_FC_LINE, COLOR_BC_LINE));
		for (int i = 0; i < 155; i++) {
			int x = random.nextInt(WIDTH);
			int y = random.nextInt(HEIGHT);
			int xl = random.nextInt(12);
			int yl = random.nextInt(12);
			img.drawLine(x, y, x + xl, y + yl);
		}

		// 取随机产生的认证码(4位数字)
		String codeValue = "";
		for (int i = 0; i < 4; i++) {
			//String rand = String.valueOf(random.nextInt(10));
			String rand = getRandomChar();
			codeValue = codeValue.concat(rand);
			img.setFont(getRandomFont());//随机字体
			// 将认证码显示到图象中
			img.setColor(getRandColor(COLOR_FC_CODE, COLOR_BC_CODE));
			img.drawString(rand, 13 * i + 6, 16);
		}
		request.getSession().setAttribute("codeValue", codeValue);
		// 图象生效
		img.dispose();
		// 输出图象到页面
		return ImageIO.write(image, "JPEG", response.getOutputStream());
	}
	
	/**
	 * 随机生成字符，含大写、小写、数字
	 * <b>function:</b> 功能
	 * @createDate 2010-8-23 上午10:33:55
	 * @author hoojo
	 * @return
	 */
	public static String getRandomChar() {
		int index = (int) Math.round(Math.random() * 2);
		String randChar = "";
		switch (index) {
		case 0://大写字符
			randChar = String.valueOf((char)Math.round(Math.random() * 25 + 65));
			break;
		case 1://小写字符
			randChar = String.valueOf((char)Math.round(Math.random() * 25 + 97));
			break;
		default://数字
			randChar = String.valueOf(Math.round(Math.random() * 9));
			break;
		}
		return randChar;
	}
	
	/**
	 * <b>function:</b> 随机生成字体、文字大小
	 * @createDate 2010-8-23 上午10:44:22
	 * @author hoojo
	 * @return
	 */
	public static Font getRandomFont() {
		String[] fonts = {"Georgia", "Verdana", "Arial", "Tahoma", "Time News Roman", "Courier New", "Arial Black", "Quantzite"};
		int fontIndex = (int)Math.round(Math.random() * (fonts.length - 1));
		int fontSize = (int) Math.round(Math.random() * 4 + 16);
		return new Font(fonts[fontIndex], Font.PLAIN, fontSize);
	}
}

其中验证码的值是保存在session中：request.getSession().setAttribute("codeValue", codeValue);
比较用户输入的值和session中的codeValue是否相等即可；

下面是jsp页面调用servlet：ValidCodeServlet.java

ValidCodeServlet中调用了上面的ValidCodeUtils 验证码生成工具类

package com.hoo.servlet;

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.hoo.util.ValidCodeUtils;

@SuppressWarnings("serial")
public class ValidCodeServlet extends HttpServlet {
	
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		try {
			ValidCodeUtils.getImage(request, response);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		doGet(request, response);
	}
}

jsp页面调用servlet方法即可

js：reloadValidCode方法

function reloadValidCode(o) {
	o.src = "${pageContext.request.contextPath }/validCodeServlet?timed=" + new Date().getMilliseconds();
}
这里的"timed=" + new Date().getMilliseconds();是需要防止IE缓存用的

html标签：
<img src="${pageContext.request.contextPath }/validCodeServlet" title="看不清，点击刷新" onclick="reloadValidCode(this)"/>
直接跟Servlet名称配置的url即可，和web.xml配置对应。主要调用路径${pageContext.request.contextPath }/validCodeServlet这样会带上根目录，比较保险。

web.xml中validCodeServlet配置
<servlet>
	<servlet-name>validCodeServlet</servlet-name>
	<servlet-class>com.hoo.servlet.ValidCodeServlet</servlet-class>
</servlet>

<servlet-mapping>
	<servlet-name>validCodeServlet</servlet-name>
	<url-pattern>/validCodeServlet</url-pattern>
</servlet-mapping>

至此，整个图片验证码就配置完毕。在浏览器中输入你请求的url，在jsp页面中就可以看到效果

怎样，效果还很理想吧。字体、大小、数字、大小写字符、及颜色等！