java servlet 写的图片验证 - 被遗忘的角落！！

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.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
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 imageservlet extends HttpServlet {

/**
* 定义字符串
*/
public static final char[] CHARS = { '2', '3', '4', '5', '6', '7', '8',
   '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L',
   'M', 'N', 'P', 'Q', 'R', 'S', 'U', 'V', 'W', 'X', 'Y', 'Z' };
//定义随机函数
public static Random random=new Random();

/**
* 生成随机字符串
*/
    public static String getString(){
    StringBuffer buffer=new StringBuffer();
    for(int i=0;i<6;i++){
      buffer.append(CHARS[random.nextInt(CHARS.length)]);

    }
    return buffer.toString();
    }
    //设置背景色
    public static Color getrandowColor(){
    return new Color(random.nextInt(255),random.nextInt(255),random.nextInt(255));
    }
    //设置前景色
    public static Color getreverseColor(Color c){
    return new Color(255-c.getRed(),255-c.getGreen(),255-c.getBlue());
    }
/**
* Constructor of the object.
*/
public imageservlet() {
  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 randomstrString=getString();
  request.getSession(true).setAttribute("randomstring",randomstrString);
  int width=100;
  int height=30;
  //新建颜色对象用于背景
  Color color=getrandowColor();
  //新建颜色对象用于前景
  Color reverse=getreverseColor(color);
  //新建图片对象
  BufferedImage bi=new BufferedImage(width,height,BufferedImage.TYPE_INT_BGR);
  Graphics2D g=bi.createGraphics();
     //设置字体
  g.setFont(new Font("仿宋体",Font.BOLD,16));
  //设置背景
  g.setColor(color);
  //填充背景色
  g.fillRect(0, 0, width, height);
  //设置前景
  g.setColor(reverse);
  //
  g.drawString(randomstrString, 18, 20);

  for(int i=0,n=random.nextInt(100);i<n;i++){
   ////画点
   g.drawRect(random.nextInt(width), random.nextInt(height), 1, 1);
   //画线
   //g.drawLine(random.nextInt(width), random.nextInt(height), random.nextInt(width),random.nextInt(width));

  }
  //新建输出对象
  ServletOutputStream out=response.getOutputStream();
  //对像装载
  JPEGImageEncoder encoder=JPEGCodec.createJPEGEncoder(out);
  //把做好的图片装入对象
  encoder.encode(bi);
  out.flush();


}

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

}

//以上导出是一个图片，只在用的地方把这个类作为图也的地址来用就ok了。。