JAVA検証コードの実現【回転】

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           ,                   : 

1.      ,                  . 
2.        . 
3.   .        ,          ,            ,            StringBuffer     ,      StringBuffer    session ,            JSP  . 

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       PAGE  :

<%@ page language="java" contentType="image/jpg;charset=gb2312" %>

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Color getRandColor(int min,int max){   //          RGB  

  Random random1=new Random();

  if(min>=255)min=255;

  if(max>=255)max=255;

  int r=min+random1.nextInt(max-min);

  int g=min+random1.nextInt(max-min);

  int b=min+random1.nextInt(max-min);

  return new Color(r,g,b);

 }

//      

  response.setHeader("Pragma","No-cache");

 response.setHeader("Cache-Control","no-cache");

 response.setDateHeader("Expires",0);

 //          ，    

 int width=60,height=20;  //       

 BufferedImage buff=new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);  //            

 Graphics g=buff.getGraphics();   //      

  graphics          :

  :

g.setColor(getRandColor(200,250));

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

   :(          )

for(int i=1;i<=30;i++){

  int x=rand.nextInt(width);  //       

  int y=rand.nextInt(height);

  int tx=rand.nextInt(12);

  int ty=rand.nextInt(12);

  g.drawLine(x,y,x+tx,y+ty);

 }

   :

String coding="";  //           

 for(int i=0;i<4;i++){

  String temp=String.valueOf(rand.nextInt(10));  //0-9   

  coding+=temp;

  //     ,20-140  

  g.setColor(getRandColor(20,140));

  g.drawString(temp,13*i+6,16);

 }

 //    session

 session.setAttribute("code",coding);

     :(       ,         )

g.dispose();

 ServletOutputStream sos=response.getOutputStream();

 ImageIO.write(buff,"jpeg",sos);

 sos.flush();  //              

 sos.close();

 sos=null;

 response.flushBuffer();

 out.clear();

 //Return a new BodyContent object, save the current "out" JspWriter, and update the value of the "out" attribute in the page scope attribute namespace of the PageContext

 out=pageContext.pushBody();