ZK - Open Source Ajax Java Framework

<zk> 
 <vlayout id="input" width="100%"> 
   <image src="/site/service/Captcha.jsp?id=myCaptcha" /> 
   Please enter the code: 
   <textbox id="code" hflex="1" /> 
   <button label="Submit"> 
    <attribute name="onClick"><![CDATA[ 
      if (code.getValue().equals( 
          Sessions.getCurrent().getNativeSession().getAttribute("myCaptcha"))) { 
        alert("Code is correct"); 
      } else { 
        alert("Code is wrong"); 
      } 
    ]]></attribute> 
   </button> 
 </vlayout> 
</zk> 

import nl.captcha.Captcha;
import nl.captcha.backgrounds.GradiatedBackgroundProducer;
import nl.captcha.text.renderer.ColoredEdgesWordRenderer;

/**
 * EN: Utility class for creating a CAPTCHA.<br>
 * Captcha can be direct loaded into a org.zkoss.zul.Image<br>
 * DE: Hilfsklasse zur Erzeugung eines CAPTCHA.<br>
 * Captcha kann direkt in ein org.zkoss.zul.Image eingelesen werden.
 * 
 * <pre>
 * Image img = new org.zkoss.zul.Image();
 * img.setContent(CaptchaUtils.getCaptcha().getImage());
 * 
 * String verifyStr = captcha.getAnswer();
 * </pre>
 * 
 * @author Stephan Gerth
 */
public class FDCaptchaUtils {

	public FDCaptchaUtils() {
	}

	/**
	 * Create a 5 digits captcha.
	 * 
	 * @return
	 */
	public static Captcha getCaptcha() {

		Captcha captcha = new Captcha.Builder(140, 50)
                        .addText(new ColoredEdgesWordRenderer()).addNoise()
                        .addBackground(new GradiatedBackgroundProducer())
                        .addBorder()
                        .build();

		return captcha;
	}

}

    . . .
						<grid sclass="GridPlain"
							style="padding-right: 15px;">
							<columns>
								<column align="right" width="180px" />
								<column />
							</columns>
							<rows>

								<!-- Captcha / Captcha -->
								<row>
									<label
										value="${c:l('common.Captcha')}" />
									<hbox>



====>>>									<image id="img_Captcha" />



										<toolbarbutton id="btnReCaptcha"
											image="/images/icons/refresh_green_16x16.gif"
											tooltiptext="${c:l('common.ReCaptcha')}" />
									</hbox>
								</row>
								<!-- Verify Captcha / Verifiziere Captcha -->
								<row>
									<label
										value="${c:l('common.Repeat')}" />
									<hbox>
										<textbox id="txtb_VerifyCaptcha"
											maxlength="6" width="140px" />
										<toolbarbutton
											id="btnVerifyCaptcha" image="/images/icons/start_16x16.gif"
											tooltiptext="${c:l('common.Check.Input')}" />
									</hbox>
								</row>
							</rows>
						</grid>

	. . .

public class ForgottenPasswordCtrl extends GenericForwardComposer implements Serializable {

   . . .
	protected Window windowForgottenPassword; // autowired

	protected Image img_Captcha; // autowired
	protected Textbox txtb_EmailAddress; // autowired
	protected Textbox txtb_VerifyCaptcha; // autowired
	protected Button btnSendPassword; // autowired

	private Captcha captcha;

   . . .

	public void onCreate$windowForgottenPassword(Event event) throws Exception {

		// Create the captcha and set it as image
		doReCaptcha(event);

		windowForgottenPassword.doModal();
	}

	public void onClick$btnClose(Event event) throws InterruptedException {...
	public void onClick$btnSendPassword(Event event) {...
	public void onClick$btnReCaptcha(Event event) {...
	public void onClick$btnVerifyCaptcha(Event event) {...

    . . .

	/**
	 * Do a re-Captcha.<br>
	 * 
	 * @param event
	 */
	private void doReCaptcha(Event event) {
		// init: disable the send password button
		btnSendPassword.setDisabled(true);

		setCaptcha(FDCaptchaUtils.getCaptcha());
		img_Captcha.setContent(getCaptcha().getImage());
	}

	/**
	 * 1. Checks if the email address is entered.<br>
	 * 2. Verify the created captcha digits against the users input from a textbox.<br>
	 * 3. Enable/disable the 'reset password' button.<br>
	 * 
	 * @param event
	 */
	private void doVerifyCaptcha(Event event) {

		// init: disable the send password button
		btnSendPassword.setDisabled(true);

		// check if the email address is entered
		if (StringUtils.isEmpty(txtb_EmailAddress.getValue())) {
			throw new WrongValueException(txtb_EmailAddress, Labels.getLabel("message.Error.CannotBeEmpty"));
		}

		// check if the captcha is verified correctly
		if (StringUtils.equals(txtb_VerifyCaptcha.getValue(), getCaptcha().getAnswer())) {
			btnSendPassword.setDisabled(false);
		}
	}

    . . .

        // +++++++++++++++++++++++++++++++++++++++++++++++++ //
	// ++++++++++++++++ Setter/Getter ++++++++++++++++++ //
	// +++++++++++++++++++++++++++++++++++++++++++++++++ //

	public void setCaptcha(Captcha captcha) {
		this.captcha = captcha;
	}

	public Captcha getCaptcha() {
		return captcha;
	}

    . . .