cn.apiclub.captcha.servlet.StickyCaptchaServlet Maven / Gradle / Ivy

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package cn.apiclub.captcha.servlet;

import static cn.apiclub.captcha.Captcha.NAME;

import java.io.IOException;
import java.util.Date;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import cn.apiclub.captcha.Captcha;

/**
 * Builds a CAPTCHA and stores it in the session. This is intended to prevent
 * bots from simply reloading the page and getting new images until one is
 * generated which they can successfully parse. Removal of the session attribute
 * CaptchaServletUtil.NAME will force a new Captcha to
 * be added to the session. (Obviously, this is not a perfect solution as
 * session IDs can simply not be passed.)
 *
 * The size of the image is by default 200x50. This can be customized using the
 * captcha-height and captcha-width init parameters in
 * web.xml.
 *
 * By default the CAPTCHA will expire after 600000ms. This can be overridden
 * using the ttl init parameter, in milliseconds.
 *
 * An example showing all parameters:
 *
 *  *    <servlet>
 *         <servlet-name>StickyCaptcha</servlet-name>
 *         <servlet-class>nl.captcha.servlet.StickyCaptchaServlet</servlet-class>
 *         <init-param>
 *             <param-name>captcha-width</param-name>
 *             <param-value>400</param-value>
 *         </init-param>
 *         <init-param>
 *             <param-name>captcha-height</param-name>
 *             <param-value>200</param-value>
 *         </init-param>
 *         <init-param>
 *             <param-name>ttl</param-name>
 *             <param-value>900000</param-value>
 *         </init-param>
 *       </servlet>
 * 
 *
 * Since the constructed image is a PNG the servlet mapping should be defined
 * something like this:
 *
 *  *     <servlet-mapping>
 *         <servlet-name>StickyCaptcha</servlet-name>
 *         <url-pattern>/stickyCaptcha.png</url-pattern>
 *     </servlet-mapping>
 * 
 * @author James Childers
 */
public class StickyCaptchaServlet extends HttpServlet {

    private static final long serialVersionUID = 40913456229L;
    
    private static int _width = 200;
    private static int _height = 50;
    
    private static long _ttl = 1000 * 60 * 10;

    @Override
    public void init(ServletConfig config) throws ServletException {
        super.init(config);
    	if (getInitParameter("captcha-height") != null) {
    		_height = Integer.valueOf(getInitParameter("captcha-height"));
    	}
    	
    	if (getInitParameter("captcha-width") != null) {
    		_width = Integer.valueOf(getInitParameter("captcha-width"));
    	}
    	
        if (getInitParameter("ttl") != null) {
            _ttl = Long.valueOf(getInitParameter("ttl"));
        }
    }

    /**
     * Write out the CAPTCHA image stored in the session. If not present,
     * generate a new Captcha and write out its image.
     * 
     */
    @Override
    public void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        HttpSession session = req.getSession();
        Captcha captcha;

        if (session.getAttribute(NAME) == null) {
            captcha = buildAndSetCaptcha(session);
        }

        captcha = (Captcha) session.getAttribute(NAME);
        if (shouldExpire(captcha)) {
            captcha = buildAndSetCaptcha(session);
        }

        CaptchaServletUtil.writeImage(resp, captcha.getImage());
    }

    private Captcha buildAndSetCaptcha(HttpSession session) {
        Captcha captcha = new Captcha.Builder(_width, _height)
            .addText()
            .gimp()
            .addBorder()
            .addNoise()
            .addBackground()
            .build();

        session.setAttribute(NAME, captcha);
        return captcha;
    }

    /**
     * Set the length of time the CAPTCHA will live in session, in milliseconds.
     * 
     * @param ttl
     */
    static void setTtl(long ttl) {
        if (ttl < 0) {
            ttl = 0;
        }

        _ttl = ttl;
    }

    /**
     * Get the time to live for the CAPTCHA, in milliseconds.
     * 
     * @return
     */
    static long getTtl() {
        return _ttl;
    }

    // Expire the CAPTCHA after a given number of minutes
    static boolean shouldExpire(Captcha captcha) {
        long ts = captcha.getTimeStamp().getTime();
        long now = new Date().getTime();
        long diff = now - ts;

        return diff >= _ttl;
    }
}