JSP中验证码

//设置页面不缓存
		response.setHeader("Pragma","No-cache");
		response.setHeader("Cache-Control","no-cache");
		response.setDateHeader("Expires", 0);

		// 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("Times New Roman",Font.PLAIN,18));

		//画边框
		//g.setColor(new Color());
		//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
		    g.drawString(rand,13*i+6,16);
		}

		// 将认证码存入SESSION
		HttpSession session = request.getSession();
		session.setAttribute("rand",sRand);


		// 图象生效
		g.dispose();

		// 输出图象到页面
		ImageIO.write(image, "JPEG", response.getOutputStream());


public 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);
}


Jsp页面<img src=”servlet/mingzi” >

如要实现单击图片更换验证码在js中img.src="servlet/mingzi?i="+ Math.random();即可