Captcha in JSP

Create a JSP Page that return Image Stream.

/* Author:- Mohammed Sajadh N.A
    Blog:- http://sajadhaja.blogspot.in
*/
<%@ 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.*"%>
<%

  String imageFormat = "jpg";
  response.setContentType("image/" + imageFormat);

 try {
   // you can pass in fontSize, width, height via the request
  
   Color backgroundColor = Color.white;
   Color borderColor = Color.black;
   Color textColor = Color.black;
   Color circleColor = new Color(160,160,160);
   Font textFont = new Font("Arial", Font.ITALIC, paramInt(request, "fontSize", 24));
   int charsToPrint = 9;
   int width = paramInt(request, "width", 150);
   int height = paramInt(request, "height", 80);
   int circlesToDraw = 6;
   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.setColor(backgroundColor);
   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.drawArc(0,0,120,120,40,20);
   }

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

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

   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();
   }

   // let's do the border
   g.setColor(borderColor);
   g.drawRect(0, 0, width - 1, height - 1);

   //Write the image as a jpg
   Iterator iter = ImageIO.getImageWritersByFormatName(imageFormat);
   if( iter.hasNext() ) {
     ImageWriter writer = (ImageWriter)iter.next();
     ImageWriteParam iwp = writer.getDefaultWriteParam();
     if ( imageFormat.equalsIgnoreCase("jpg") || imageFormat.equalsIgnoreCase("jpeg") ) {
       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
   System.out.println("Captcha is:- "+finalString);
   request.getSession().setAttribute("captcha", finalString.toString());

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

%>
<%!
  public static String paramString(HttpServletRequest request, String paramName, String defaultString) {
    return request.getParameter(paramName) != null ? request.getParameter(paramName) : defaultString;
  }

  public static int paramInt(HttpServletRequest request, String paramName, int defaultInt) {
    return request.getParameter(paramName) != null ? Integer.parseInt(request.getParameter(paramName)) : defaultInt;
  }
%>