以下為專案中所用程式碼，文筆有限，直接上程式碼。

所需jar包：

是否需要其他依賴包，不詳

web.xml

<servlet>
     <servlet-name>Jcaptcha</servlet-name>
     <servlet-class>com.bkgd.cms.servlet.JcaptchaServlet</servlet-class>
</servlet>
<servlet-mapping>
     <servlet-name>Jcaptcha</servlet-name>
     <url-pattern>/captcha.svl</url-pattern>
</servlet-mapping>
 

package com.bkgd.cms.servlet;

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 org.apache.commons.io.output.ByteArrayOutputStream;
import org.apache.log4j.Logger;
import com.octo.captcha.service.CaptchaServiceException;
import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;

@SuppressWarnings("serial")
public class JcaptchaServlet extends HttpServlet {
	public static final String CAPTCHA_IMAGE_FORMAT = "jpeg";

	private static final Logger log = Logger.getLogger(JcaptchaServlet.class);

	@Override
	public void init() throws ServletException {
	}

	/**
	 * @step1 本方法使用Jcaptcha工具生成img圖片，並輸出到客戶端
	 * @step2 將來在使用者提交的action中插入下面語句進行驗證碼的校驗：Boolean isResponseCorrect =
	 *        captchaService.validateResponseForID( captchaId, "");
	 **/
	@Override
	protected void doGet(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		byte[] captchaChallengeAsJpeg = null;
		ByteArrayOutputStream jpegOutputStream = new ByteArrayOutputStream();
		try {
			// 藉助於HttpSession ID儲存Captcha ID，開發者也可以藉助於其他惟一值
			String captchaId = request.getSession().getId();
			// 獲得GMailEngine使用的圖片內容
			BufferedImage challenge = JCaptchaServiceSingleton.getInstance().getImageChallengeForID(captchaId, request.getLocale());
			// 輸出JPEG格式
			JPEGImageEncoder jpegEncoder = JPEGCodec.createJPEGEncoder(jpegOutputStream);
			jpegEncoder.encode(challenge);
		} catch (IllegalArgumentException e) {
			log.error(e);
			response.sendError(HttpServletResponse.SC_NOT_FOUND);
			return;
		} catch (CaptchaServiceException e) {
			log.error(e);
			response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
			return;
		}
		captchaChallengeAsJpeg = jpegOutputStream.toByteArray();
		response.setHeader("Cache-Control", "no-store");
		response.setHeader("Pragma", "no-cache");
		response.setDateHeader("Expires", 0);
		// 輸出JPEG圖片
		response.setContentType("image/jpeg");
		ServletOutputStream responseOutputStream = response.getOutputStream();
		responseOutputStream.write(captchaChallengeAsJpeg);
		responseOutputStream.flush();
		responseOutputStream.close();
	}
}
 

package com.bkgd.cms.servlet;

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

public class JCaptchaServiceSingleton {
	private static ImageCaptchaService imageCaptchaService = new DefaultManageableImageCaptchaService(
			new FastHashMapCaptchaStore(), new GMailEngine(), 180, 100000,
			75000);

	public static ImageCaptchaService getInstance() {
		return imageCaptchaService;
	}
}
 

package com.bkgd.cms.servlet;

import java.awt.Color;
import java.awt.Font;
import java.awt.image.ImageFilter;

import com.octo.captcha.component.image.backgroundgenerator.BackgroundGenerator;
import com.octo.captcha.component.image.backgroundgenerator.UniColorBackgroundGenerator;
import com.octo.captcha.component.image.color.RandomListColorGenerator;
import com.octo.captcha.component.image.deformation.ImageDeformation;
import com.octo.captcha.component.image.deformation.ImageDeformationByFilters;
import com.octo.captcha.component.image.fontgenerator.FontGenerator;
import com.octo.captcha.component.image.fontgenerator.RandomFontGenerator;
import com.octo.captcha.component.image.textpaster.DecoratedRandomTextPaster;
import com.octo.captcha.component.image.textpaster.TextPaster;
import com.octo.captcha.component.image.textpaster.textdecorator.TextDecorator;
import com.octo.captcha.component.image.wordtoimage.DeformedComposedWordToImage;
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;

/**
 * 仿照JCaptcha2.0編寫GMail驗證碼樣式的圖片引擎.
 */
public class GMailEngine extends ListImageCaptchaEngine {
	@Override
	protected void buildInitialFactories() {
		int minWordLength = 4;
		int maxWordLength = 4;
		int fontSize = 26;
		int imageWidth = 110;
		int imageHeight = 50;
		//在頁面上將顯示的內容
		WordGenerator dictionnaryWords = new RandomWordGenerator("1234567890");
		TextPaster randomPaster = new DecoratedRandomTextPaster(minWordLength,
				maxWordLength, new RandomListColorGenerator(
						new Color[] { new Color(0, 0, 0) }),
				new TextDecorator[] {});
		BackgroundGenerator background = new UniColorBackgroundGenerator(
				imageWidth, imageHeight, Color.white);
		FontGenerator font = new RandomFontGenerator(fontSize, fontSize,
				new Font[] { new Font("nyala", Font.BOLD, fontSize),
						new Font("Bell MT", Font.PLAIN, fontSize),
						new Font("Credit valley", Font.BOLD, fontSize) });

		ImageDeformation postDef = new ImageDeformationByFilters(new ImageFilter[] {});
		ImageDeformation backDef = new ImageDeformationByFilters(new ImageFilter[] {});
		ImageDeformation textDef = new ImageDeformationByFilters(new ImageFilter[] {});

		WordToImage word2image = new DeformedComposedWordToImage(font,
				background, randomPaster, backDef, textDef, postDef);
		addFactory(new GimpyFactory(dictionnaryWords, word2image));
	}

}

<input class="input" type="text" name="checkCode" id="checkCode" value=""/>
<img id="captcha" src="captcha.svl" onclick="this.src='captcha.svl?d='+new Date()*1"/>

HttpServletRequest request = ServletActionContext.getRequest();
String sessID = request.getSession().getId();
Boolean isResponseCorrect = JCaptchaServiceSingleton.getInstance().validateResponseForID(sessID, checkCode);
if(isResponseCorrect){
	return "true"
}else{
	return "false"	
}