这样的实现方式对JDK版本有要求。
 1 package edu.cloud.editmap.utils;

 import java.awt.Color;

 import java.awt.Font;

 import java.awt.Graphics2D;

 import java.awt.image.BufferedImage;

 import java.io.IOException;

 import java.util.Random;

 import javax.servlet.ServletOutputStream;

 import javax.servlet.http.HttpServletRequest;

 import javax.servlet.http.HttpServletResponse;

 import com.sun.image.codec.jpeg.JPEGCodec;

 import com.sun.image.codec.jpeg.JPEGImageEncoder;

 public class IdentityCode {

     private static final long serialVersionUID = -479885884254942306L;

     public static final char[] CHARS = { '2', '3', '4', '5', '6', '7', '8',

             '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'J', 'K', 'L', 'M',

             'N', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z' };

     public static Random random = new Random();

     public static String getRandomString() {

         StringBuffer buffer = new StringBuffer();

         for (int i = 0; i < 4; i++) {

             buffer.append(CHARS[random.nextInt(CHARS.length)]);

         }

         return buffer.toString();

     }

     public static Color getRandomColor() {

         return new Color(random.nextInt(255), random.nextInt(255), random

                 .nextInt(255));

     }

     public static Color getReverseColor(Color c) {

         return new Color(255 - c.getRed(), 255 - c.getGreen(), 255 - c

                 .getBlue());

     }

     public static void createImage(HttpServletResponse response,HttpServletRequest request){

         response.setContentType("image/jpeg");

         String randomString = getRandomString();

         System.out.println(randomString);

         request.getSession().setAttribute("indentity_code", randomString);

         int width = 100;

         int height = 30;

         Color color = getRandomColor();

         Color reverse = getReverseColor(color);

         BufferedImage bi = new BufferedImage(width, height,

                 BufferedImage.TYPE_INT_RGB);

         Graphics2D g = bi.createGraphics();

         g.setFont(new Font(Font.SANS_SERIF, Font.BOLD, 16));

         g.setColor(color);

         g.fillRect(0, 0, width, height);

         g.setColor(reverse);

         g.drawString(randomString, 18, 20);

         for (int i = 0, n = random.nextInt(100); i < n; i++) {

             g.drawRect(random.nextInt(width), random.nextInt(height), 1, 1);

         }

         // 转成JPEG格式

         try {

             ServletOutputStream out = response.getOutputStream();

             JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);

             encoder.encode(bi);

             out.flush();

         } catch (IOException e) {

             e.printStackTrace();

         }

     }

 }