mathcommentauthenticator.java

这个weblogging 设计得比较精巧

package org.roller.presentation.velocity;

import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import org.apache.velocity.context.Context;
import org.roller.pojos.CommentData;
import org.roller.presentation.RollerSession;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import java.util.ResourceBundle;

/**
 * Asks the commenter to answer a simple math question.
 * @author David M Johnson
 */
public class MathCommentAuthenticator implements CommentAuthenticator 
{   
    private transient ResourceBundle bundle = 
        ResourceBundle.getBundle("ApplicationResources");
    
    private static Log mLogger =
        LogFactory.getFactory().getInstance(MathCommentAuthenticator.class);

    public String getHtml(
                        Context context,
                        HttpServletRequest request, 
                        HttpServletResponse response)
    {
        String answer = "";
        HttpSession session = request.getSession();
        if (session.getAttribute("mathAnswer") == null)
        {
            // starting a new test
            int value1 = (int)(Math.random()*10.0);
            int value2 = (int)(Math.random()*100.0);
            int sum = value1 + value2;
            session.setAttribute("mathValue1", new Integer(value1));
            session.setAttribute("mathValue2", new Integer(value2));
            session.setAttribute("mathAnswer", new Integer(sum));
        }
        else
        {
            // preserve user's answer
            answer = request.getParameter("answer");
            answer = (answer == null) ? "" : answer;
        }

        // pull existing values out of session
        Integer value1o = 
            (Integer)request.getSession().getAttribute("mathValue1");
        Integer value2o = 
            (Integer)request.getSession().getAttribute("mathValue2");
        
        StringBuffer sb = new StringBuffer();
        
        sb.append("<p>");
        sb.append(bundle.getString("comments.mathAuthenticatorQuestion"));
        sb.append("</p><p>");
        sb.append(value1o);
        sb.append(" + ");
        sb.append(value2o);
        sb.append(" = ");
        sb.append("<input name=\"answer\" value=\"");
        sb.append(answer);
        sb.append("\" /></p>");
        
        return sb.toString();
    }
    
    public boolean authenticate(
                        CommentData comment,
                        HttpServletRequest request) 
    {
        boolean ret = false;
        String answerString = request.getParameter("answer");
        if (answerString != null || answerString.trim().length()==0)
        {
            try 
            {   
                int answer = Integer.parseInt(answerString);
                Integer sum = 
                    (Integer)request.getSession().getAttribute("mathAnswer");            
                if (answer == sum.intValue()) 
                {
                    ret = true;           
                    request.getSession().removeAttribute("mathAnswer");
                    request.getSession().removeAttribute("mathValue1");
                    request.getSession().removeAttribute("mathValue2");
                }
            }
            catch (NumberFormatException ignored) {}
            catch (Exception e) 
            {
                mLogger.error(e);
            }
        }
        return ret;
    }
}