（个人笔记）生成验证码

public class getImg extends HttpServlet {

//处理post
public void doPost(HttpServletRequest request,HttpServletResponse response)
throws ServletException,IOException {
doGet(request,response);
}
public void doGet(HttpServletRequest request,HttpServletResponse response)
throws ServletException,IOException {
	
	
	HttpSession session=request.getSession(true);
	response.setContentType("image/gif");
	ServletOutputStream out1=response.getOutputStream();
	//在内存中创建图象
	int width=60, height=20;
	BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
	//获取图形上下文
	Graphics g = image.getGraphics();
	//生成随机类
	Random random = new Random();
	// 设定背景色
	//g.setColor(getRandColor(200,250));
	g.fillRect(0, 0, width, height);
	//设定字体
	g.setFont(new Font("Monotype Corsiva",Font.BOLD,18));
	//画边框
	g.setColor(Color.BLACK);
	g.drawRect(0,0,width-1,height-1);
	
	// 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到
//	g.setColor(getRandColor(160,200));
//	for (int i=0;i<155;i++)
//	{
//		int x = random.nextInt(width);
//		int y = random.nextInt(height);
//		int xl = random.nextInt(12);
//		int yl = random.nextInt(12);
//		g.drawLine(x,y,x+xl,y+yl);
//	}
	
	// 取随机产生的认证码(4位数字)
	String sRand="";
	for (int i=0;i<4;i++){
	    String rand=String.valueOf(random.nextInt(10));
	    sRand+=rand;
	    // 将认证码显示到图象中
	    g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));//调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
	    if(i%2==0){
	    	g.drawString(rand,13*i+6,16+2);
	    }else{
	    	g.drawString(rand,13*i+6,16-2);
	    }
	}
	
	session.setAttribute("validateCode",sRand);//对session赋值

	JPEGImageEncoder encoder=JPEGCodec.createJPEGEncoder(out1);
	encoder.encode(image);
	
	out1.close();

}

	Color getRandColor(int fc,int bc){//给定范围获得随机颜色
        Random random = new Random();
        if(fc>255) fc=255;
        if(bc>255) bc=255;
        int r=fc+random.nextInt(bc-fc);
        int g=fc+random.nextInt(bc-fc);
        int b=fc+random.nextInt(bc-fc);
        return new Color(r,g,b);
        }


}

<img src="<%=request.getContextPath()%>/getImg" >