.NET Core 中生成验证码

在开发中，有时候生成验证码的场景目前还是存在的，本篇演示不依赖第三方组件，生成随机验证码图片。

先添加验证码接口

public interface ICaptcha {     /// <summary>     /// 生成随机验证码     /// </summary>     /// <param name="codeLength"></param>     /// <returns></returns>     Task<string> GenerateRandomCaptchaAsync(int codeLength = 4);      /// <summary>     /// 生成验证码图片     /// </summary>     /// <param name="captchaCode">验证码</param>     /// <param name="width">宽为0将根据验证码长度自动匹配合适宽度</param>     /// <param name="height">高</param>     /// <returns></returns>     Task<CaptchaResult> GenerateCaptchaImageAsync(string captchaCode, int width = 0, int height = 30); } 

验证码返回模型

public class CaptchaResult {     /// <summary>     /// CaptchaCode     /// </summary>     public string CaptchaCode { get; set; }      /// <summary>     /// CaptchaMemoryStream     /// </summary>     public MemoryStream CaptchaMemoryStream { get; set; }      /// <summary>     /// Timestamp     /// </summary>     public DateTime Timestamp { get; set; } } 

接下来实现接口，主要是依赖微软的System.Drawing.Common组件，注意命名空间的引用

using System; using System.Drawing; using System.Drawing.Imaging; using System.IO; using System.Threading.Tasks;  ...  public class Captcha : ICaptcha {     private const string Letters = "1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,J,K,L,M,N,P,Q,R,S,T,U,V,W,X,Y,Z";      public Task<CaptchaResult> GenerateCaptchaImageAsync(string captchaCode, int width = 0, int height = 30)     {         //验证码颜色集合         Color[] c = { Color.Black, Color.Red, Color.DarkBlue, Color.Green, Color.Orange, Color.Brown, Color.DarkCyan, Color.Purple };          //验证码字体集合         string[] fonts = { "Verdana", "Microsoft Sans Serif", "Comic Sans MS", "Arial" };          //定义图像的大小，生成图像的实例         var image = new Bitmap(width == 0 ? captchaCode.Length * 25 : width, height);          var g = Graphics.FromImage(image);          //背景设为白色         g.Clear(Color.White);          var random = new Random();          for (var i = 0; i < 100; i++)         {             var x = random.Next(image.Width);             var y = random.Next(image.Height);             g.DrawRectangle(new Pen(Color.LightGray, 0), x, y, 1, 1);         }          //验证码绘制在g中         for (var i = 0; i < captchaCode.Length; i++)         {             //随机颜色索引值             var cindex = random.Next(c.Length);              //随机字体索引值             var findex = random.Next(fonts.Length);              //字体             var f = new Font(fonts[findex], 15, FontStyle.Bold);              //颜色               Brush b = new SolidBrush(c[cindex]);              var ii = 4;             if ((i + 1) % 2 == 0)                 ii = 2;              //绘制一个验证字符               g.DrawString(captchaCode.Substring(i, 1), f, b, 17 + (i * 17), ii);         }          var ms = new MemoryStream();         image.Save(ms, ImageFormat.Png);          g.Dispose();         image.Dispose();          return Task.FromResult(new CaptchaResult         {             CaptchaCode = captchaCode,             CaptchaMemoryStream = ms,             Timestamp = DateTime.Now         });     }      public Task<string> GenerateRandomCaptchaAsync(int codeLength = 4)     {         var array = Letters.Split(new[] { ',' });          var random = new Random();          var temp = -1;          var captcheCode = string.Empty;          for (int i = 0; i < codeLength; i++)         {             if (temp != -1)                 random = new Random(i * temp * unchecked((int)DateTime.Now.Ticks));              var index = random.Next(array.Length);              if (temp != -1 && temp == index)                 return GenerateRandomCaptchaAsync(codeLength);              temp = index;              captcheCode += array[index];         }          return Task.FromResult(captcheCode);     } } 

在控制器中注入调用

using Microsoft.AspNetCore.Mvc; using System.Threading.Tasks;  [Route("api/[controller]")] [ApiController] public class CaptchaController : ControllerBase {     [HttpGet]     public async Task<FileContentResult> CaptchaAsync([FromServices] ICaptcha _captcha)     {         var code = await _captcha.GenerateRandomCaptchaAsync();          var result = await _captcha.GenerateCaptchaImageAsync(code);          return File(result.CaptchaMemoryStream.ToArray(), "image/png");     } } 

实际使用的时候，code就是本次生成的验证码，可以将其保存在session中，进行验证，或者其它方式。