Servlet代码生成验证码

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package com.test;

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

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

public class TestIMGEServlet extends HttpServlet {

private static final long serialVersionUID = 1L;
public static final String VALIDATE_CODE_SESSION_KEY="VALIDATE_CODE_SESSION_KEY";
public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  doPost(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  response.setContentType("image/png");
  String code = createValidateCode();
  request.getSession().setAttribute(VALIDATE_CODE_SESSION_KEY, code);
  Color []c = new Color[]{Color.RED,Color.BLUE,Color.green,Color.BLACK};
  //生成这么大小的图片
  BufferedImage image = new BufferedImage(120, 40, BufferedImage.TYPE_INT_RGB);
  //生成画笔
  Graphics g = image.getGraphics();
  //把生成的图片的背景色设置一下淡灰色的
  g.setColor(Color.GRAY.brighter());
  g.fillRect(0, 0, image.getWidth(), image.getHeight());
  Random r = new Random();
  for (int i = 0; i < 20; i++) {
   g.setColor(new Color(r.nextInt(256), r.nextInt(256), r.nextInt(256)));
   g.drawOval(r.nextInt(image.getWidth())/2, r.nextInt(image.getHeight())/2, r.nextInt(image.getWidth()), r.nextInt(image.getHeight()));

  }
  Font f = new Font("IMPACT", Font.BOLD, 30);
  g.setFont(f);
  for (int i = 0; i < code.length(); i++) {
   int y = r.nextInt(20)+20;
   //g.setColor(Color.black);
   //g.drawString(""+code.charAt(i), image.getWidth()/code.length()*i, 20);
   g.setColor(c[i]);
   g.drawString(""+code.charAt(i), image.getWidth()/code.length()*i, y);
  }
  System.out.println(request.getSession().getAttribute(VALIDATE_CODE_SESSION_KEY));
  ImageIO.write(image, "png", response.getOutputStream());


}
public String createValidateCode(){
  String charNumber = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
  Random r = new Random();
  return ""+charNumber.charAt(r.nextInt(charNumber.length()))+charNumber.charAt(r.nextInt(charNumber.length()))+charNumber.charAt(r.nextInt(charNumber.length()))+charNumber.charAt(r.nextInt(charNumber.length()));
}

}