Introduction

Marc Schipperheyn (m.schipperheynNOSPAMMERSgmail.com) gratefully contributed the following documentation on how to use Kaptcha with Spring. I don't personally use Spring so please contact him with any questions you have.

Details

security.xml

<bean id="captchaProducer"
	class="com.google.code.kaptcha.impl.DefaultKaptcha">
	<property name="config">
		<bean class="com.google.code.kaptcha.util.Config">
			<constructor-arg type="java.util.Properties" value="null"></constructor-arg>
		</bean>
	</property>
</bean>

To use properties:

<bean id="captchaProducer"
	class="com.google.code.kaptcha.impl.DefaultKaptcha">
	<property name="config">
		<bean class="com.google.code.kaptcha.util.Config">
			<constructor-arg type="java.util.Properties">
				<props>
					<prop key="kaptcha.image.width">300</prop> 
					<prop key="kaptcha.image.height">25</prop>
					<prop key="kaptcha.textproducer.char.string">0123456789</prop>
					<prop key="kaptcha.textproducer.char.length">4</prop>
				</props>
			</constructor-arg>
		</bean>
	</property>
</bean>

Kaptcha controller

package nl.yourproject.webapp.controller;

import java.awt.image.BufferedImage;

import javax.imageio.ImageIO;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.servlet.ModelAndView;

import com.google.code.kaptcha.Constants;
import com.google.code.kaptcha.Producer;

@Controller
public class CaptchaImageCreateController {
	private Producer captchaProducer = null;
	
	@Autowired
	public void setCaptchaProducer(Producer captchaProducer) {
		this.captchaProducer = captchaProducer;
	}

	@RequestMapping("/captcha-image.html")
	public ModelAndView handleRequest(
			HttpServletRequest request,
			HttpServletResponse response) throws Exception {
		// Set to expire far in the past.
		response.setDateHeader("Expires", 0);
		// Set standard HTTP/1.1 no-cache headers.
		response.setHeader("Cache-Control", "no-store, no-cache, must-revalidate");
		// Set IE extended HTTP/1.1 no-cache headers (use addHeader).
		response.addHeader("Cache-Control", "post-check=0, pre-check=0");
		// Set standard HTTP/1.0 no-cache header.
		response.setHeader("Pragma", "no-cache");
		  
		// return a jpeg
		response.setContentType("image/jpeg");

		// create the text for the image
		String capText = captchaProducer.createText();
		
		// store the text in the session
		request.getSession().setAttribute(Constants.KAPTCHA_SESSION_KEY, capText);

		// create the image with the text
		BufferedImage bi = captchaProducer.createImage(capText);

		ServletOutputStream out = response.getOutputStream();
		
		// write the data out
		ImageIO.write(bi, "jpg", out);
		try
		{
			out.flush();
		}
		finally
		{
			out.close();
		}
		return null;
	}
}

Kaptcha check in regular controller

package nl.yourproject.webapp.controller;
import java.util.HashMap;
import java.util.Map;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import nl.msw.compraventa.VO.RegistrationVO;
import nl.msw.compraventa.validator.RegistrationValidator;

import org.apache.commons.lang.StringUtils;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.beans.BeanUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.validation.BindingResult;
import org.springframework.validation.Errors;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

import com.google.code.kaptcha.Constants;
import com.google.code.kaptcha.Producer;

@Controller
@RequestMapping("/register.html")
public class RegistrationFormController {

	private Log log = LogFactory.getLog(RegistrationFormController.class);
	private Producer captchaProducer;

	@Autowired
	public void setCaptchaService(Producer captchaProducer) {
		this.captchaProducer = captchaProducer;
	}

	@RequestMapping(method = RequestMethod.GET)
	public String setupForm(
			ModelMap model,
			HttpServletRequest request,
			HttpServletResponse response) throws Exception {
		RegistrationVO vo = new RegistrationVO();
		model.addAttribute("vo", vo);

		return "registrationform";
	}

	@RequestMapping(method = RequestMethod.POST)
	public String processForm(
			@ModelAttribute("vo")
			RegistrationVO vo,
			BindingResult result,
			ModelMap model,
			HttpServletRequest request,
			HttpServletResponse response) throws Exception {

			 validateCaptcha(request, (Object) vo, (Errors) result);

		//handle your form
		return "registrationform";
	}


	/**
	 * Validate the captcha response
	 */
	protected void validateCaptcha(
			HttpServletRequest request,
			Object command,
			Errors errors) throws Exception {
		String captchaId = (String) request.getSession().getAttribute(Constants.KAPTCHA_SESSION_KEY);
		String response = ((RegistrationVO) command).getCaptchaResponse();

		if (log.isDebugEnabled()) {
			log.debug("Validating captcha response: '" + response + "'");
		}

		if (!StringUtils.equalsIgnoreCase(captchaId, response)) {
			errors.rejectValue("captchaResponse", "error.invalidcaptcha",
					"Invalid Entry");
		}
	}
}