JSP Servlet实现验证码

package net.cmono.javaweb.c3;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Random;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.sun.corba.se.impl.ior.NewObjectKeyTemplateBase;
import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;

public class IdentityServlet extends HttpServlet {

    /**
     * Constructor of the object.
*/
    public IdentityServlet() {
        super();
    }

    /**
     * Destruction of the servlet. <br>
*/
    public void destroy() {
        super.destroy(); // Just puts "destroy" string in log
// Put your code here
    }

    /**
     * The doGet method of the servlet. <br>
     *
     * This method is called when a form has its tag value method equals to get.
     * 
     * @param request the request send by the client to the server
     * @param response the response send by the server to the client
     * @throws ServletException if an error occurred
     * @throws IOException if an error occurred
*/
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        response.setContentType("image/jpeg");
        
        String randomString = getRandomString();
        request.getSession(true).setAttribute("randomString",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);
        }
        
        ServletOutputStream out = response.getOutputStream();
        
        JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
        
        encoder.encode(bi);
        
        out.flush();
        
    }

    /**
     * The doPost method of the servlet. <br>
     *
     * This method is called when a form has its tag value method equals to post.
     * 
     * @param request the request send by the client to the server
     * @param response the response send by the server to the client
     * @throws ServletException if an error occurred
     * @throws IOException if an error occurred
*/
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        
    }

    /**
     * Initialization of the servlet. <br>
     *
     * @throws ServletException if an error occurs
*/
    public void init() throws ServletException {
        // Put your code here
    }

    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 < 6;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());
    }
    
}

<script type="text/javascript">
function reloadImage()
  {
     document.getElementById('btn').disabled = true;
     document.getElementById('identity').src='servlet/IndentityServlet?ts' + new Date().getTime();
  }
</script>

<img src="servlet/IdentityServlet" id="identity" onload="btn.disabled = false;"

<input type="button" value="换张图片" onclick="reloadImage()" id="btn" />