ASP.net 验证码实现代码(C#)

ASP.NET 验证码实现代码(C#)攻略

前言

验证码是一种常用的安全验证手段，用于防止恶意机器人注册、登录、提交表单等操作。本篇文章将介绍如何在ASP.NET中使用C#实现验证码功能。

实现过程

1. 生成随机字符串

首先，我们需要生成一串随机字符串，作为验证码。可以使用Random类和StringBuilder类来生成：

Random random = new Random();
StringBuilder sb = new StringBuilder();
for (int i = 0; i < 4; i++)
{
    int code = random.Next(65, 91); // Generate the verification code with the ASCII value of A to Z
    sb.Append((char)code); // Convert the ASCII code to character and append it to the StringBuilder
}
string verCode = sb.ToString();

2. 将验证码存入Session

生成验证码之后，我们需要将其存储在Session中，以便于后面的验证。可以使用如下代码：

Session["VerificationCode"] = verCode;

3. 绘制验证码图片

接下来，我们需要将验证码绘制成一张图片。可以使用GDI+绘图库，将随机字符串绘制在一张空白图片上。代码如下所示：

Bitmap bitmap = new Bitmap(100, 30); // Create an empty image with the width of 100 and the height of 30
Graphics graphics = Graphics.FromImage(bitmap); // Get the graphics object of the image
// Set the font and color of the string to be drawn
Font font = new Font("Arial", 18, FontStyle.Bold);
SolidBrush brush = new SolidBrush(Color.Black);
graphics.DrawString(verCode, font, brush, 10, 5); // Draw the string on the image

4. 输出图片

最后一步是将生成的验证码图片输出到客户端。可以将图片以二进制形式输出，如下所示：

MemoryStream ms = new MemoryStream(); // Create a memory stream to store the image
bitmap.Save(ms, ImageFormat.Jpeg); // Save the image to the memory stream in JPEG format
Response.ClearContent(); // Clear the response buffer
Response.ContentType = "image/Jpeg"; // Set the content type of the response to image/Jpeg
Response.BinaryWrite(ms.ToArray()); // Write the image to the response

示例说明

示例1： 在ASP.NET网页中使用验证码

在ASP.NET网页中使用验证码，可以防止机器人恶意注册或登录。下面是一个简单的示例，展示如何在ASP.NET网页中使用上述代码实现验证码功能：

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        GenerateVerificationCode(); // Generate a verification code when the page first loads
    }
}

protected void btnSubmit_Click(object sender, EventArgs e)
{
    if (txtVerificationCode.Text.Trim().Equals(Session["VerificationCode"].ToString(), StringComparison.OrdinalIgnoreCase))
    {
        // Verification succeeded, do something...
    }
    else
    {
        // Verification failed, do something...
        GenerateVerificationCode(); // Generate a new verification code and refresh the image
    }
}

private void GenerateVerificationCode()
{
    Random random = new Random();
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < 4; i++)
    {
        int code = random.Next(65, 91); // Generate the verification code with the ASCII value of A to Z
        sb.Append((char)code); // Convert the ASCII code to character and append it to the StringBuilder
    }
    string verCode = sb.ToString();
    Session["VerificationCode"] = verCode;

    Bitmap bitmap = new Bitmap(100, 30); // Create an empty image with the width of 100 and the height of 30
    Graphics graphics = Graphics.FromImage(bitmap); // Get the graphics object of the image
    Font font = new Font("Arial", 18, FontStyle.Bold); // Set the font and color of the string to be drawn
    SolidBrush brush = new SolidBrush(Color.Black);
    graphics.DrawString(verCode, font, brush, 10, 5); // Draw the string on the image

    MemoryStream ms = new MemoryStream(); // Create a memory stream to store the image
    bitmap.Save(ms, ImageFormat.Jpeg); // Save the image to the memory stream in JPEG format
    Response.ClearContent(); // Clear the response buffer
    Response.ContentType = "image/Jpeg"; // Set the content type of the response to image/Jpeg
    Response.BinaryWrite(ms.ToArray()); // Write the image to the response
    graphics.Dispose(); // Dispose the graphics object
    bitmap.Dispose(); // Dispose the bitmap object
}

示例2： 将验证码封装为ASP.NET自定义控件

将验证码封装为ASP.NET自定义控件，可以将其易于重用，并且可以更加方便地设置外观和行为。下面是一个简单的示例，展示如何将验证码封装为ASP.NET自定义控件：

public class VerificationCodeControl : WebControl, INamingContainer
{
    private string _verCode;

    [DefaultValue(4)]
    public int Length { get; set; } = 4;

    public string FontFamily { get; set; } = "Arial";

    public int FontSize { get; set; } = 18;

    protected override void OnInit(EventArgs e)
    {
        base.OnInit(e);
        GenerateVerificationCode(); // Generate a verification code when the control is initialized
        this.Attributes["src"] = this.Page.ResolveUrl("~/VerificationCode.ashx"); // Set the source of the image to the ASHX handler
    }

    private void GenerateVerificationCode()
    {
        Random random = new Random();
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < Length; i++)
        {
            int code = random.Next(65, 91); // Generate the verification code with the ASCII value of A to Z
            sb.Append((char)code); // Convert the ASCII code to character and append it to the StringBuilder
        }
        _verCode = sb.ToString();
        this.Page.Session["VerificationCode"] = _verCode;
    }

    protected override void AddAttributesToRender(HtmlTextWriter writer)
    {
        writer.AddAttribute(HtmlTextWriterAttribute.Alt, "Verification Code");
        writer.AddAttribute(HtmlTextWriterAttribute.Class, this.CssClass);
        writer.AddAttribute(HtmlTextWriterAttribute.Style, $"font-family: {FontFamily}; font-size: {FontSize}px;");
        base.AddAttributesToRender(writer);
    }

    protected override void RenderContents(HtmlTextWriter writer)
    {
        writer.Write(_verCode); // Render the verification code as plain text (fallback for non-HTML5 browser)
        base.RenderContents(writer);
    }
}

上述代码会生成一个继承自WebControl的VerificationCodeControl控件，可以在ASP.NET网页中方便地使用。比如，可以在ASPX页面中使用以下代码：

<%@ Register TagPrefix="Custom" Namespace="MyNamespace" %>
<Custom:VerificationCodeControl ID="VerificationCode1" runat="server" Length="6" FontSize="30" />

这里演示的是如何将生成验证码的逻辑封装为自定义控件，并且使用ASHX处理程序来输出验证码图片。稍微修改一下ASHX处理程序即可。

结语

本文介绍了如何使用C#在ASP.NET中实现验证码功能，并且提供了两个简单的示例。通过使用验证码，可以提高网站的安全性和可靠性，避免恶意机器人、蜘蛛等程序对网站造成的风险和威胁。

参考资料

• C# 验证码验证码的实现
• CodeProject - Generate and verify CAPTCHA image in ASP.NET