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 ;
}
}