servlet简单验证码的实现

@WebServlet(description="annotation",urlPatterns={"/dynamicP"},loadOnStartup=1)

public class DynamicPicture extends HttpServlet {                       //首先声明验证码随机出现的字符数组，这里简写。                                       public static final char[] chars={'1','2','3','4','5','6','7','8','9',                                                                                         'a','b','c','d','e','f','g','h','i','j','k','A','B','C','D','E'                                                                                                                                            ,'F','G','H','I','J','K','M','N'};                                                       public static Random random = new Random(); public static String getRandomString()//随机产生五个 { StringBuilder buffer = new StringBuilder(); for(int i = 0;i < 5;i++) { buffer.append(chars[random.nextInt(chars.length)]); } return buffer.toString(); } public static Color getRandomColor()//随机颜色,用于背景色 { return new Color(random.nextInt(255),random.nextInt(255),random.nextInt(255)); } public static Color getReverseColor(Color c)//返回某种颜色的反色，用于前景色 { return new Color(255-c.getRed(),255-c.getGreen(),255-c.getBlue()); } public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("image/jpeg"); String randomString = getRandomString(); request.getSession(true).setAttribute("randomString", randomString);//传入session，验证时使用 //开始画图 int width=110; int height=40; Color color=getRandomColor(); Color reverse=getReverseColor(color); BufferedImage bI = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB); Graphics2D g = bI.createGraphics(); g.setFont(new Font(Font.SANS_SERIF,Font.BOLD,25)); g.setColor(color); g.fillRect(0, 0, width, height);//绘制背景 g.setColor(reverse); g.drawString(randomString, 15, 28); for(int i=0,n=random.nextInt(100);i<n;i++)//用来画点 { g.drawRect(random.nextInt(width), random.nextInt(height), 1, 1); } //画图结束 ServletOutputStream out = response.getOutputStream(); JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out); encoder.encode(bI); out.flush(); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } }

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