驗證碼的使用

驗證碼使用的非常普遍,在很多大型,小型網站中經常看到,我想這樣做肯定是有一定的道理,今天在網上搜索了一下,實現原理主要是這樣的,先在源文檔中加入一個圖片控件,使其src屬性指向一個***.aspx文件,這個文件生成一個隨機的驗證碼圖標,存入session或者是cookies值中,

,在需要驗證的頁面再根據輸入的值和session或者是cookies的值進行對比.

<asp:Image id="Image1" runat="server" ImageUrl="ValidateCode.aspx" ImageAlign="Middle" />

<a onclick="ChangeImage();" style="cursor:hand;">看不清楚,換一張</a>

***.aspx.cs后台代碼如下:

protected void Page_Load(object sender, EventArgs e)

{

this.CreateCheckCodeImage(GenerateCheckCode());

}

//生成一個隨機的字符串

private string GenerateCheckCode()

{

int number;

char code;

string checkCode = String.Empty;

System.Random random = new Random();

for (int i = 0; i < 5; i++)

{

number = random.Next();

if (number % 2 == 0)

code = (char)('0' + (char)(number % 10));

else

code = (char)('A' + (char)(number % 26));

checkCode += code.ToString();

}

Session["VNum"] = checkCode;

Response.Cookies.Add(new HttpCookie("VNum", checkCode));

return checkCode;

}

//對驗證碼字符串進行修飾,並輸出

private void CreateCheckCodeImage(string checkCode)

{

if (checkCode == null || checkCode.Trim() == String.Empty)

return;

System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 22);

System.Drawing.Graphics g = Graphics.FromImage(image);

try

{

//生成随机生成器

Random random = new Random();

//清空图片背景色

g.Clear(Color.White);

//画图片的背景噪音线

for (int i = 0; i < 25; i++)

{

int x1 = random.Next(image.Width);

int x2 = random.Next(image.Width);

int y1 = random.Next(image.Height);

int y2 = random.Next(image.Height);

g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);

}

Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));

System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);

g.DrawString(checkCode, font, brush, 2, 2);

//画图片的前景噪音点

for (int i = 0; i < 100; i++)

{

int x = random.Next(image.Width);

int y = random.Next(image.Height);

image.SetPixel(x, y, Color.FromArgb(random.Next()));

}

//画图片的边框线

g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);

System.IO.MemoryStream ms = new System.IO.MemoryStream();

image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);

Response.ClearContent();

Response.ContentType = "image/Gif";

Response.BinaryWrite(ms.ToArray());

}

finally

{

g.Dispose();

image.Dispose();

}

}