随机生成图片验证码

 public class Img extends HttpServlet {

	@Override
	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		//设置Content-Type响应头
		response.setContentType("image/jpeg");
		//下面三条语句用于设置页面不缓存
		response.setHeader("Pragma", "No-cache");
		response.setHeader("Cache-Control", "no-cache");
		response.setDateHeader("Expires", 0);

		OutputStream out = response.getOutputStream();
		int width = 80;
		int height = 20;

		//建立指定宽、高和BufferedImage对象
		BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
		Graphics g = image.getGraphics();

		//随机生成类
		Random random = new Random();
		//生成背景色
		g.setColor(getRandColor(200,250)); 

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

		// 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); 
		} 

		//设置字体
		g.setFont(new Font("Times New Roman",Font.ITALIC,18));
		String sRand = "";
		for(int i = 0; i < 4 ; i++){
			String rand = String.valueOf(random.nextInt(10));
			sRand += rand;
			//设置随机颜色
			g.setColor(new Color(20 + random.nextInt(110),20 + random.nextInt(110),20 + random.nextInt(110)));
			//绘制
			g.drawString(rand, 20*i + 6, 16);
		}

		g.dispose();
		//输出图像到页面
		ImageIO.write(image, "JPEG", out);	
	}

         //给定范围获得随机颜色 
	private Color getRandColor(int fc,int bc){		    
         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); 
	} 
}

web.xml配置:
<servlet>
		<servlet-name>img</servlet-name>
		<servlet-class>com.servlet.Img</servlet-class>
	</servlet>
	<servlet-mapping>
		<servlet-name>img</servlet-name>
		<url-pattern>/test</url-pattern>
	</servlet-mapping>

JSP应用:
<img alt="" src="/test">, src是url-pattern的值