Captcha生成及使用

@Controller

@RequestMapping("/PictureCheckCode")

public class ServletController {

    @RequestMapping

    public void pictureGenerate( HttpServletRequest req, HttpServletResponse res ) {

        try {

             MakePicture mp=new MakePicture() ;

             String str=mp.drawPicture(60, 20,res.getOutputStream() );

             req.getSession().setAttribute("pic", str);

             res.getOutputStream().print(str);

        }

        catch(Exception ex) {

            ex.printStackTrace();

        }

    }

}

<form th:action="@{/login}" method="post">

            <div><label> User Name : <input type="text" name="username"/> </label></div>

            <div><label> Password: <input type="password" name="password"/> </label></div>

            <div><label> Verify: <img src="PictureCheckCode"  onclick="this.src='PictureCheckCode?d='+new Date().getTime()"/> </label></div>

            <div><input type="submit" value="Sign In"/></div>

</form>

package hello;

import java.awt.Graphics;

import java.awt.Font;

import java.awt.Color;

import java.awt.image.BufferedImage;

import javax.imageio.ImageIO;

import java.util.Random;

import java.io.OutputStream;

import java.io.IOException;

public class MakePicture  //产生识别验证图像

{

	private char charTable[]={

		'a','A','b','B','c','C','d','D' ,'e','E' ,

		'f','F','g','G','h','H','i','I','j','J' ,

		'0','1','2','3','4','5','6','7','8','9'

	};

	public String drawPicture(int width,int height,OutputStream os)

	{

		if(width<=0)

			width=100 ;

		if(height<=0)

			height=60 ;

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

		Graphics g=image.getGraphics()  ;

		g.setColor(Color.LIGHT_GRAY) ;

		g.fillRect(0, 0, width, height)  ;

		g.setColor(new Color(0x5265fd)) ;

		g.drawRect(0, 0, width, height)  ;

		String str ="" ;

		for(int x=0;x<4;x++)

		{

		  str+=charTable[(int) (Math.random()*charTable.length)];

		}

		g.drawString(str.substring(0, 1), 0, 15);

		g.drawString(str.substring(1, 2), 15, 17);

		g.drawString(str.substring(2, 3), 35, 19);

		g.drawString(str.substring(3, 4), 50, 16);

		Random rand=new Random() ;

		for(int i=0;i<10;i++)

		{

		  int x=rand.nextInt(width)  ;

		  int y=rand.nextInt(height)  ;

		  g.drawOval(x, y, 1, 1) ;

 		}

		g.dispose()  ;

		try {

			ImageIO.write(image, "JPEG",os) ;

		} catch (IOException e) {

			e.printStackTrace();

			return "" ;

		}

	   return str ;

	}

}