动态刷新实现图片验证码

java实现图片验证码
ImageGenerator 生成一张包含四位随机数的图片 
Java代码 
package com.my.page;   
  
import java.awt.Color;   
import java.awt.Font;   
import java.awt.Graphics;   
import java.awt.image.BufferedImage;   
import java.io.OutputStream;   
import java.util.Random;   
  
import javax.imageio.ImageIO;   
import javax.servlet.http.HttpServlet;   
import javax.servlet.http.HttpServletRequest;   
import javax.servlet.http.HttpServletResponse;   
  
/**  
 * 这个class主要实现随机生成一个4位数的验证码，并写入session，  
 */  
  
public class ImageGenerator extends HttpServlet {   
       
      private static Color getRandColor(int fc, int bc) {   
        Random random = new Random();   
        if (fc > 255)   
            fc = 255;   
        if (bc > 255)   
            bc = 255;   
        int r = fc + random.nextInt(bc - fc);   
        int g = fc + random.nextInt(bc - fc);   
        int b = fc + random.nextInt(bc - fc);   
        return new Color(r, g, b);   
    }   
  
      private static String charsLong = "23456789abcdefghjklmnpqrstuvwxyzABCDEFGHIJKLMNPQRSTUVWXYZ";   
  
      private static String charsShort = "0123456789";   
  
      private static String chars = charsLong;   
  
      @Override  
    public void doGet(HttpServletRequest request, HttpServletResponse response) {   
        try {   
            int charsLength = chars.length();   
  
            response.setHeader("Pragma", "No-cache");   
            response.setHeader("Cache-Control", "no-cache");   
            response.setDateHeader("Expires", 0);   
  
            int width = 75, height = 20;   
            BufferedImage image = new BufferedImage(width, height,   
                    BufferedImage.TYPE_INT_RGB);   
  
            Graphics g = image.getGraphics();   
  
            Random random = new Random();   
  
            g.setColor(getRandColor(200, 250));   
            g.fillRect(0, 0, width, height);   
  
            g.setFont(new Font("Times New Roman", Font.ITALIC, height));   
  
            g.setColor(getRandColor(160, 200));   
            for (int i = 0; i < 35; i++) {   
                int x = random.nextInt(width);   
                int y = random.nextInt(height);   
                int xl = random.nextInt(12);   
                int yl = random.nextInt(12);   
                g.drawLine(x, y, x + xl, y + yl);   
            }   
  
            StringBuilder sRand = new StringBuilder();   
            String[] fontNames = { "Times New Roman", "Arial", "Book antiqua",   
                    "" };   
  
          for (int i = 0; i < 4; i++) {   
                g.setFont(new Font(fontNames[random.nextInt(3)], Font.ITALIC,   
                        height));   
                char rand = chars.charAt(random.nextInt(charsLength));   
                sRand.append(rand);   
  
                g.setColor(new Color(20 + random.nextInt(110), 20 + random   
                        .nextInt(110), 20 + random.nextInt(110)));   
                g.drawString(String.valueOf(rand), 16 * i + random.nextInt(6)   
                        + 3, height - random.nextInt(4));   
            }   
  
          g.setColor(getRandColor(160, 200));   
          for (int i = 0; i < 19; i++) {   
                int x = random.nextInt(width);   
                int y = random.nextInt(height);   
                int xl = random.nextInt(width);   
                int yl = random.nextInt(width);   
                g.drawLine(x, y, x + xl, y + yl);   
            }   
  
          request.getSession().setAttribute("Login_Image_Code",   
                    sRand.toString());   
  
          g.dispose();   
  
          try {   
                Thread.sleep(100);   
            } catch (Exception ex) {   
            }   
            OutputStream os = response.getOutputStream();   
            ImageIO.write(image, "JPEG", os);   
            os.flush();   
            os.close();   
        } catch (Exception ex) {   
  
        }   
    }   
  
}  

package com.my.page;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.OutputStream;
import java.util.Random;

import javax.imageio.ImageIO;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * 这个class主要实现随机生成一个4位数的验证码，并写入session，
 */

public class ImageGenerator extends HttpServlet {
 
   private static Color getRandColor(int fc, int bc) {
  Random random = new Random();
  if (fc > 255)
   fc = 255;
  if (bc > 255)
   bc = 255;
  int r = fc + random.nextInt(bc - fc);
  int g = fc + random.nextInt(bc - fc);
  int b = fc + random.nextInt(bc - fc);
  return new Color(r, g, b);
 }

   private static String charsLong = "23456789abcdefghjklmnpqrstuvwxyzABCDEFGHIJKLMNPQRSTUVWXYZ";

   private static String charsShort = "0123456789";

   private static String chars = charsLong;

   @Override
 public void doGet(HttpServletRequest request, HttpServletResponse response) {
  try {
   int charsLength = chars.length();

   response.setHeader("Pragma", "No-cache");
   response.setHeader("Cache-Control", "no-cache");
   response.setDateHeader("Expires", 0);

   int width = 75, height = 20;
   BufferedImage image = new BufferedImage(width, height,
     BufferedImage.TYPE_INT_RGB);

   Graphics g = image.getGraphics();

   Random random = new Random();

   g.setColor(getRandColor(200, 250));
   g.fillRect(0, 0, width, height);

   g.setFont(new Font("Times New Roman", Font.ITALIC, height));

   g.setColor(getRandColor(160, 200));
   for (int i = 0; i < 35; i++) {
    int x = random.nextInt(width);
    int y = random.nextInt(height);
    int xl = random.nextInt(12);
    int yl = random.nextInt(12);
    g.drawLine(x, y, x + xl, y + yl);
   }

   StringBuilder sRand = new StringBuilder();
   String[] fontNames = { "Times New Roman", "Arial", "Book antiqua",
     "" };

       for (int i = 0; i < 4; i++) {
    g.setFont(new Font(fontNames[random.nextInt(3)], Font.ITALIC,
      height));
    char rand = chars.charAt(random.nextInt(charsLength));
    sRand.append(rand);

    g.setColor(new Color(20 + random.nextInt(110), 20 + random
      .nextInt(110), 20 + random.nextInt(110)));
    g.drawString(String.valueOf(rand), 16 * i + random.nextInt(6)
      + 3, height - random.nextInt(4));
   }

       g.setColor(getRandColor(160, 200));
       for (int i = 0; i < 19; i++) {
    int x = random.nextInt(width);
    int y = random.nextInt(height);
    int xl = random.nextInt(width);
    int yl = random.nextInt(width);
    g.drawLine(x, y, x + xl, y + yl);
   }

       request.getSession().setAttribute("Login_Image_Code",
     sRand.toString());

       g.dispose();

       try {
    Thread.sleep(100);
   } catch (Exception ex) {
   }
   OutputStream os = response.getOutputStream();
   ImageIO.write(image, "JPEG", os);
   os.flush();
   os.close();
  } catch (Exception ex) {

     }
 }

}


在web.xml加入一下内容 
Java代码 
<servlet>   
    <servlet-name>imageGenerator</servlet-name>   
<servlet-class>com.my.page.ImageGenerator</servlet-class>   
 </servlet>   
  <servlet-mapping>   
    <servlet-name>imageGenerator</servlet-name>   
    <url-pattern>/image.jpg</url-pattern>   
 </servlet-mapping>  

 <servlet>
   <servlet-name>imageGenerator</servlet-name>
 <servlet-class>com.my.page.ImageGenerator</servlet-class>
  </servlet>
   <servlet-mapping>
   <servlet-name>imageGenerator</servlet-name>
   <url-pattern>/image.jpg</url-pattern>
  </servlet-mapping>


运用 
Java代码 
<input type="text" class="txt" wicket:id="validate"/><br/>   
<img src="image.jpg" onclick= "this.src= 'image.jpg? '+(new   Date()) "/>  
其中onclick事件作用是：单击该验证图片，进行刷新，实现看不清换一张的效果