image validation code generation

RandomCodeServlet.java

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

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


public class RandomCodeServlet extends HttpServlet {
	 private static final long serialVersionUID = 1L; 

	//驗證碼圖片的寬度
	    private int width=85; 
	//驗證碼圖片的高度
	    private int height=20; 
	//隨機的字數
	    private int codeCount=4; 


	    private int x=0; 
	//字體的高度
	    private int fontHeight; 
	    private int codeY; 

	    char[] codeSequence = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',
	                'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W',
	                'X', 'Y', 'Z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' }; 

	
	    public void init() throws ServletException{
	        //字體寬度
	        String strWidth=this.getInitParameter("width"); 
	        //字體的高度
	        String strHeight=this.getInitParameter("height"); 
	        //字體的字數
	        String strCodeCount=this.getInitParameter("codeCount"); 
	    
	        //逕行判斷
	        try{
	            if(strWidth!=null && strWidth.length()!=0){
	                width=Integer.parseInt(strWidth); 
	            }
	            if(strHeight!=null && strHeight.length()!=0){
	                height=Integer.parseInt(strHeight); 
	            }
	            if(strCodeCount!=null && strCodeCount.length()!=0){
	                codeCount=Integer.parseInt(strCodeCount); 
	            }
	        }catch(NumberFormatException e){
	            e.printStackTrace();
	        }
	        
	        x=width/(codeCount+2); 
	        fontHeight=height-2; 
	        codeY=height-4; 
	    
	    }
	    
	    protected void service(HttpServletRequest req, HttpServletResponse resp)throws ServletException, java.io.IOException {
	    
	        
	        BufferedImage buffImg = new BufferedImage(width, height,BufferedImage.TYPE_INT_RGB); 
	        Graphics2D g = buffImg.createGraphics(); 
	        
	      //創建一個隨機器生成器類
	        Random random = new Random(); 
	        
	        
	        g.setColor(Color.WHITE); 
	        g.fillRect(0, 0, width, height); 
	        
	      //創建字體,字體的大小隨圖片的高度來定
	        Font font = new Font("Fixedsys", Font.PLAIN, fontHeight); 
	      //設置字體
	        g.setFont(font); 
	        
	        //畫邊框
	        g.setColor(Color.BLACK); 
	        g.drawRect(0, 0, width - 1, height - 1); 
	        
	      //隨機產生160條干擾線,是圖像中的驗證碼不易被其他程序探測到
	        g.setColor(Color.GRAY); 
	        for(int i = 0; i<160; i++) {
	            int x = random.nextInt(width); 
	            int y = random.nextInt(height); 
	            int xl = random.nextInt(1); 
	            int yl = random.nextInt(1); 
	            g.drawLine(x, y, x + xl, y + yl); 
	        }
	        
	        //randomCodeç用於保存隨機產生的驗證碼,以便於用戶注冊時逕行驗證
	        StringBuffer randomCode = new StringBuffer(); 
	        int red = 0, green = 0, blue = 0; 
	        
	        //隨機產生4位數字的驗證碼
	        for (int i = 0; i<codeCount; i++) {
	        	//得到隨機產生的驗證碼數字
	            String strRand = String.valueOf(codeSequence[random.nextInt(36)]); 
	          //產生隨機的顏色分量來構造顏色值,這樣輸出的每位數字的顏色值都將不同
	            red = random.nextInt(110); 
	            green = random.nextInt(50); 
	            blue = random.nextInt(50); 
	            
	          //用隨機產生的顏色將驗證碼會知道圖像中
	            g.setColor(new Color(red, green, blue)); 
	            g.drawString(strRand, (i + 1) * x, codeY); 
	            
	          //將產生的四個隨機數組合在一起
	            randomCode.append(strRand); 
	        }
	     // 將產生的隨機數存貯在session中
	        HttpSession session = req.getSession(); 
	        //resp.addHeader("P3P", "CP=CAO PSA OUR"); 
	        //resp.setHeader("P3P","CP='IDC DSP COR ADM DEVi TAIi PSA PSD IVAi IVDi CONi HIS OUR IND CNT'");
	        session.removeAttribute("validateCode");
	        session.setAttribute("validateCode", randomCode.toString());
	     // 禁止圖像緩存
	        resp.setHeader("Pragma", "no-cache"); 
	        resp.setHeader("Cache-Control", "no-cache"); 
	        resp.setDateHeader("Expires", 0); 
	        
	        resp.setContentType("image/jpeg"); 
	        
	        //將圖像輸出的servlet流中
	        ServletOutputStream sos = resp.getOutputStream(); 
	        ImageIO.write(buffImg, "jpeg", sos); 
	        sos.close(); 
	    }
}

generated a random 4 numbers and letters virification code