CalcCaptcha

This is the source code for a simple captcha that looks like this :

The servlet is easy customizable so you can easy edit it or write your own.

The Captcha is based on the 100 lines JSP captcha explained here : http://www.jroller.com/mlconnor/entry/simple_captcha_jsp

package com.joke.web.servetls;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import com.joke.service.Constants;

import java.awt.Color;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Iterator;

import javax.imageio.IIOImage;
import javax.imageio.ImageIO;
import javax.imageio.ImageWriteParam;
import javax.imageio.ImageWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class CaptchaServlet extends HttpServlet {
/**
  * Logger for this class
  */
private static final Log logger = LogFactory.getLog(CaptchaServlet.class);

/**
  * 
  */
private static final long serialVersionUID = -3425450129222434319L;

/*
  * Constants
  */
private static final String SESSION_PARAM_CAPTCHA_IMAGE = Constants.SESSION_PARAM_DEFAULT_CAPTCHA_IMAGE;
private static final String IMAGE_MIME_TYPE_JPG = "image/jpg";
private static final String CAPTCHA_FONT = "Arial";
private static final String REQUEST_PARAM_HEIGHT = "height";
private static final String REQUEST_PARAM_WIDTH = "width";

// private static final int MAX_LINES_TO_DRAW = 6;
// private static final int MIN_LINES_TO_DRAW = 2;
private static final int MAX_CIRCLES_TO_DRAW = 10;
private static final int MIN_CIRCLES_TO_DRAW = 6;

@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 doGet(req, resp);
}

@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 logger.debug("Generating captcha...");

 response.setContentType(IMAGE_MIME_TYPE_JPG);
 try {

  Color backgroundColor = new Color(240, 244, 247);

  Color textColor = new Color(131, 153, 184);

  Color circleColor = new Color(195, 208, 247);
  Font textFont = new Font(CAPTCHA_FONT, Font.PLAIN, 24);
  int charsToPrint = 5;
  int width = request.getParameter(REQUEST_PARAM_WIDTH) != null ? Integer.parseInt(request
    .getParameter(REQUEST_PARAM_WIDTH)) : 150;
  int height = request.getParameter(REQUEST_PARAM_HEIGHT) != null ? Integer.parseInt(request
    .getParameter(REQUEST_PARAM_HEIGHT)) : 30;

  float horizMargin = 20.0f;
  float imageQuality = 0.95f; // max is 1.0 (this is for jpeg)
  double rotationRange = 0.7; // this is radians
  BufferedImage bufferedImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);

  Graphics2D g = (Graphics2D) bufferedImage.getGraphics();
  g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
  // Draw an oval
  g.setColor(backgroundColor);
  g.fillRect(0, 0, width, height);

  // lets make some noisy circles
  int circlesToDraw = (int) (Math.random() * (MAX_CIRCLES_TO_DRAW - MIN_CIRCLES_TO_DRAW))
    + MIN_CIRCLES_TO_DRAW;

  for (int i = 0; i < circlesToDraw; i++) {
   g.setColor((i % 2 == 0) ? (circleColor) : (new Color(circleColor.getRed(), 123 + (int) (Math.random() * 122),
     circleColor.getGreen())));

   int circleWidth = (int) ((Math.random() * width / 2.0) * (Math.random() * 2));
   int circleHeight = (int) ((Math.random() * height / 2.0) * (Math.random() * 2));
   int circleX = (int) (Math.random() * width - circleWidth);
   int circleY = (int) (Math.random() * height - circleHeight);

   g.drawOval(circleX, circleY, circleWidth, circleHeight);
  }

//   // lets make some noisy lines
//   int linesToDraw = (int) (Math.random() * (MAX_LINES_TO_DRAW - MIN_LINES_TO_DRAW)) + MIN_LINES_TO_DRAW;
//   for (int i = 0; i < linesToDraw; i++) {
//    g.setColor((i % 2 == 0) ? (textColor) : (new Color(textColor.getRed(), (int) (Math.random() * 255),
//      textColor.getGreen())));
//
//    g.drawLine((int) (Math.random() * width), (int) (Math.random() * height),
//      (int) (Math.random() * width), (int) (Math.random() * height));
//   }

  g.setColor(textColor);
  g.setFont(textFont);

  FontMetrics fontMetrics = g.getFontMetrics();
  int maxAdvance = fontMetrics.getMaxAdvance();
  int fontHeight = fontMetrics.getHeight();

  // i removed 1 and l and i because there are confusing to users...
  // Z, z, and N also get confusing when rotated
  // 0, O, and o are also confusing...
  // lowercase G looks a lot like a 9 so i killed it
  // this should ideally be done for every language...
  // i like controlling the characters though because it helps prevent confusion
  String elegibleChars = "123456789";
  char[] chars = elegibleChars.toCharArray();

  float spaceForLetters = -horizMargin * 2 + width;
  float spacePerChar = spaceForLetters / (charsToPrint - 1.0f);

  StringBuffer finalString = new StringBuffer();

  for (int i = 0; i < charsToPrint; i++) {
   double randomValue = Math.random();
   int randomIndex = (int) Math.round(randomValue * (chars.length - 1));

   char characterToShow = chars[randomIndex];
   if (i == 2) {
    characterToShow = '+';
   } else if (i == 4) {
    characterToShow = '=';
   }
   finalString.append(characterToShow);

   // this is a separate canvas used for the character so that
   // we can rotate it independently
   int charWidth = fontMetrics.charWidth(characterToShow);
   int charDim = Math.max(maxAdvance, fontHeight);
   int halfCharDim = (charDim / 2);

   BufferedImage charImage = new BufferedImage(charDim, charDim, BufferedImage.TYPE_INT_ARGB);
   Graphics2D charGraphics = charImage.createGraphics();
   charGraphics.translate(halfCharDim, halfCharDim);
   double angle = (Math.random() - 0.5) * rotationRange;
   if (!(characterToShow == '+' || characterToShow == '=')) {
    charGraphics.transform(AffineTransform.getRotateInstance(angle));
   }
   charGraphics.translate(-halfCharDim, -halfCharDim);
   charGraphics.setColor(textColor);
   charGraphics.setFont(textFont);

   int charX = (int) (0.5 * charDim - 0.5 * charWidth);
   charGraphics.drawString("" + characterToShow, charX,
     ((charDim - fontMetrics.getAscent()) / 2 + fontMetrics.getAscent()));

   float x = horizMargin + spacePerChar * (i) - charDim / 2.0f;
   int y = ((height - charDim) / 2);
   // System.out.println("x=" + x + " height=" + height + " charDim=" + charDim + " y=" + y + " advance=" +
   // maxAdvance + " fontHeight=" + fontHeight + " ascent=" + fontMetrics.getAscent());
   g.drawImage(charImage, (int) x, y, charDim, charDim, null, null);

   charGraphics.dispose();
  }

  // Write the image as a jpg
  Iterator<ImageWriter> iter = ImageIO.getImageWritersByFormatName("JPG");
  if (iter.hasNext()) {
   ImageWriter writer = iter.next();
   ImageWriteParam iwp = writer.getDefaultWriteParam();
   iwp.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
   iwp.setCompressionQuality(imageQuality);
   writer.setOutput(ImageIO.createImageOutputStream(response.getOutputStream()));
   IIOImage imageIO = new IIOImage(bufferedImage, null, null);
   writer.write(null, imageIO, iwp);
  } else {
   logger.error("doGet(HttpServletRequest, HttpServletResponse) - no encoder found for jsp.");
   throw new RuntimeException("no encoder found for jsp");
  }
  // ImageIO.write(bufferedImage, "jpg", response.getOutputStream());

  // let's stick the final string in the session
  int firstDigit = Integer.parseInt(finalString.substring(0, 2));
  int secoundDigit = Integer.parseInt(finalString.substring(3, 4));
  int result = firstDigit + secoundDigit;

  logger.debug("Generated captcha code:" + result);

  request.getSession().setAttribute(SESSION_PARAM_CAPTCHA_IMAGE, String.valueOf(result));

  g.dispose();
  response.flushBuffer();
 } catch (IOException ioe) {
  logger.error("doGet(HttpServletRequest, HttpServletResponse)", ioe);
  throw new RuntimeException("Unable to build image", ioe);
 }

}

}