100 Line Captcha JSP (See related posts)

100 Line Captcha JSP


Simple, nice looking captcha implemented in 100 lines of JSP. Easily change font, colors, size, and captcha characters. Since it's a JSP you can rewrite it to do whatever the heck you want to do. Enjoy!!! ...and send me any improvements you make

<%@ page import="java.util.*"%>
<%@ page import="java.io.*"%>
<%@ page import="javax.servlet.*"%>
<%@ page import="javax.servlet.http.*"%>
<%@ page import="java.awt.*"%>
<%@ page import="java.awt.image.*"%>
<%@ page import="javax.imageio.*"%>
<%@ page import="java.awt.geom.*"%>
<%
 //========================================================
 // Kick Ass Captcha JSP
 //
 // Michael Connor 2007
 //
 // I just couldn't handle the thought of downloading a
 // big jar and configuring some servlet.xml and having
 // little to no control of anything...
 // You can send in height and width parameters.
 // The captcha value will be placed in the session in
 // a parameter called 'captcha'
 //
 // Feel free to use this code and do whatever the hell
 // you want to it.
 //========================================================

 response.setContentType("image/jpg");

 try {
   
   Color backgroundColor = Color.red;
   Color borderColor = Color.red;
   Color textColor = Color.white;
   Color circleColor = new Color(160,160,160);
   Font textFont = new Font("Arial", Font.PLAIN, 24);
   int charsToPrint = 6;
   int width = request.getParameter("width") != null ? Integer.parseInt(request.getParameter("width")) : 150;
   int height = request.getParameter("height") != null ? Integer.parseInt(request.getParameter("height")) : 80;
   int circlesToDraw = 4;
   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();

   //Draw an oval
   g.setColor(Color.red);
   g.fillRect(0, 0, width, height);

   // lets make some noisey circles
   g.setColor(circleColor);
   for ( int i = 0; i < circlesToDraw; i++ ) {
     int circleRadius = (int) (Math.random() * height / 2.0);
     int circleX = (int) (Math.random() * width - circleRadius);
     int circleY = (int) (Math.random() * height - circleRadius);
     g.drawOval(circleX, circleY, circleRadius * 2, circleRadius * 2);
   }

   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 = "ABCDEFGHJKLMPQRSTUVWXYabcdefhjkmnpqrstuvwxy23456789";
   char[] chars = elegibleChars.toCharArray();

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

   AffineTransform transform = g.getTransform();

   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];
     finalString.append(characterToShow);

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

     float x = horizMargin + spacePerChar * (i) - charDim / 2.0f;
     int y = (int) ((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 iter = ImageIO.getImageWritersByFormatName("JPG");
   if( iter.hasNext() ) {
     ImageWriter writer = (ImageWriter)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 {
     throw new RuntimeException("no encoder found for jsp");
   }

   // let's stick the final string in the session
   request.getSession().setAttribute("captcha", finalString.toString());

   g.dispose();
 } catch (IOException ioe) {
   throw new RuntimeException("Unable to build image" , ioe);
 }
%>