servlet实现验证码

package org.tools;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.util.Random;

public class Image {
    private BufferedImage image;
    private String num;
    private Image(){}
    public BufferedImage getImage() {
        return image;
    }
    public void setImage(BufferedImage image) {
        this.image = image;
    }
    public String getNum() {
        return num;
    }
    public void setNum(String num) {
        this.num = num;
    }
    public static Image getnewImage(){
        int width=75,height=20;
        Random rand=new Random();
        Image image=new Image();
        BufferedImage bim=new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
        Graphics graph=bim.getGraphics();
        graph.setFont(new Font("宋体", Font.PLAIN, 18));
        graph.setColor(new Color(200,240,rand.nextInt(rand.nextInt(250-20)+20)));
        graph.fillRect(0, 0, width, height);
        
        String text="";
        for(int i=1;i<5;i++){
            String pint="";
            int n=rand.nextInt(91);
            if(n>=65){
                text+=((char)n);
                pint=(char)n+"";
            }else{
                n=rand.nextInt(10);
                text+=n;
                pint=n+"";
            }
            graph.setColor(new Color(20+rand.nextInt(110),20+rand.nextInt(110),20+rand.nextInt(110)));
            graph.drawString(pint, 15*i, 15);
        }
        graph.dispose();
        
        image.setImage(bim);
        image.setNum(text);
        return image;
    }
}

package org.tools;

import java.io.IOException;

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

@SuppressWarnings("serial")
public class CheckNumServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        this.doPost(request, response);
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        Image image=Image.getnewImage();
        request.getSession().setAttribute("checkNum", image.getNum());
        ImageIO.write(image.getImage(), "JPEG", response.getOutputStream());
    }

}

  <servlet>
    <servlet-name>CheckNumServlet</servlet-name>
    <servlet-class>org.tools.CheckNumServlet</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>CheckNumServlet</servlet-name>
    <url-pattern>/CheckNumServlet</url-pattern>
  </servlet-mapping>

<img src="CheckNumServlet">