用html+servlet实现的验证码

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);

}

}

html部分

<td style="margin-left:9px"><img alt="dynamic picture" src="dynamicP" id="identity" style="margin:auto;"></td>