Java 随机生成验证码(支持大小写字母、数字、随机字体)的实例

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="${pageContext.request.contextPath }/validCodeServlet" onclick="reloadValidCode(this)"/>
直接跟Servlet名称配置的url即可，和web.xml配置对应。主要调用路径${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>