jcaptcha图片验证码使用范例

最后效果图：

1.首先下载jcaptcha的jar包，网上一搜，进入官网便可下载，这里不多累赘叙述。
2.把jcaptcha，commons-collections，commons-logging的jar包放入项目中。（此处commons-collections，commons-logging包需要到网上另外下载）
3.建立一个验证码引擎或者说验证码方案类CaptchaEngine，代码贴上

package hoking.in.jcaptcha;

import java.awt.Color;
import java.awt.Font;

import com.octo.captcha.component.image.backgroundgenerator.BackgroundGenerator;
import com.octo.captcha.component.image.backgroundgenerator.FunkyBackgroundGenerator;
import com.octo.captcha.component.image.fontgenerator.FontGenerator;
import com.octo.captcha.component.image.fontgenerator.RandomFontGenerator;
import com.octo.captcha.component.image.textpaster.RandomTextPaster;
import com.octo.captcha.component.image.textpaster.TextPaster;
import com.octo.captcha.component.image.wordtoimage.ComposedWordToImage;
import com.octo.captcha.component.image.wordtoimage.WordToImage;
import com.octo.captcha.component.word.wordgenerator.RandomWordGenerator;
import com.octo.captcha.component.word.wordgenerator.WordGenerator;
import com.octo.captcha.engine.image.ListImageCaptchaEngine;
import com.octo.captcha.image.gimpy.GimpyFactory;

/**
 * 验证码引擎-->彩色验证码
 */
public class CaptchaEngine extends ListImageCaptchaEngine {

	protected void buildInitialFactories() {
		// 随机生成的字符
		WordGenerator wordGenerator = new RandomWordGenerator("0123456789");
		// 文字显示的个数
		TextPaster textPaster = new RandomTextPaster(4, 5, Color.WHITE);
		// 图片的大小
		BackgroundGenerator backgroundGenerator = new FunkyBackgroundGenerator(
				80, 30);
		// 字体格式
		Font[] fontsList = new Font[] { new Font("Arial", 0, 10),
				new Font("Tahoma", 0, 10), new Font("Verdana", 0, 10)};
		// 文字的大小
		FontGenerator fontGenerator = new RandomFontGenerator(new Integer(16),
				new Integer(20), fontsList);

		WordToImage wordToImage = new ComposedWordToImage(fontGenerator,
				backgroundGenerator, textPaster);
		addFactory(new GimpyFactory(wordGenerator, wordToImage));
	}
}

4.建立一个验证码生成类CaptchaServiceSingleton（采用单例模式）

package hoking.in.jcaptcha;

import com.octo.captcha.service.captchastore.FastHashMapCaptchaStore;
import com.octo.captcha.service.image.DefaultManageableImageCaptchaService;
import com.octo.captcha.service.image.ImageCaptchaService;


/**
 * 验证码图片生成类--->单例类
 */
public class CaptchaServiceSingleton {

	private static ImageCaptchaService instance = 
		new DefaultManageableImageCaptchaService(new FastHashMapCaptchaStore(),
			new CaptchaEngine(),
			180,
			100000,
			75000);


	private CaptchaServiceSingleton(){}
	
    public static ImageCaptchaService getInstance(){
        return instance;
    }
    
}

5.创建一个Servlet，用它来向叶面输出一个图片验证码import java.awt.image.BufferedImage;

package hoking.in.jcaptcha;

import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
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 com.octo.captcha.service.CaptchaServiceException;
import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;

/**
 * 产生一个图片验证码到输出流
 */
public class ImageCaptchaServlet extends HttpServlet {

	private static final long serialVersionUID = -3718663907013663827L;

	protected void doGet(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {

		byte[] captchaChallengeAsJpeg = null;
		//创建一个字节数组输出流实例
		ByteArrayOutputStream jpegOutputStream = new ByteArrayOutputStream();
		try {
			//获取当前session ID
			String captchaId = request.getSession().getId();

			//利用验证码生成类生成验证码的缓存图片实例
			BufferedImage challenge = CaptchaServiceSingleton.getInstance()
					.getImageChallengeForID(captchaId, request.getLocale());

			//JPEG图片编码器
			JPEGImageEncoder jpegEncoder = JPEGCodec
					.createJPEGEncoder(jpegOutputStream);
			jpegEncoder.encode(challenge);
		} catch (IllegalArgumentException e) {
			response.sendError(HttpServletResponse.SC_NOT_FOUND);
			return;
		} catch (CaptchaServiceException e) {
			response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
			return;
		}
		//获取图片验证码的字节数组
		captchaChallengeAsJpeg = jpegOutputStream.toByteArray();

		// 添加以下响应头字段：要求客户端不缓存响应消息体内容
		response.setHeader("Cache-Control", "no-store");
		response.setHeader("Pragma", "no-cache");
		response.setDateHeader("Expires", 0);
		//设置响应内容类型
		response.setContentType("image/jpeg");
		
		ServletOutputStream sos = response.getOutputStream();
		//把图片验证码的字节数组输出到输出流中
		sos.write(captchaChallengeAsJpeg);
		sos.flush();
		sos.close();
	}
}

至此，使用到的3个类全部完成
6.把servlet配置到web.xml中

<servlet>
    <servlet-name>ImageValidate</servlet-name>
    <servlet-class>hoking.in.jcaptcha.ImageCaptchaServlet</servlet-class>
</servlet>

<servlet-mapping>
    <servlet-name>ImageValidate</servlet-name>
    <url-pattern>/jcaptcha</url-pattern>
</servlet-mapping>

7.编写JSP页面

<a href="javascript:void(0);" onclick="document.getElementById('imageValidate').src='${pageContext.request.contextPath }/jcaptcha?' + Math.random();">
    <img src="${pageContext.request.contextPath }/jcaptcha" border="0" alt="看不清,请点击图片换一张" id="imageValidate"> 看不清,点这换一张 </a>

OK，所有工作完成，部署项目运行之后就能看到效果图上的效果

另外附上后台验证代码

//获取当前用户的session ID
String sessionId = requset.getSession().getId();
//获取用户提交的验证码
String captcha = requset.getParameter("imageValidate");
boolean flag = false;
//进行验证
flag = CaptchaServiceSingleton.getInstance().validateResponseForID(sessionId, captcha);

到此全部结束

最后来一张项目结构图



摘自：http://blog.csdn.net/hoking_in/article/details/7902380