简单验证码的制作
网站上验证码效果一般制作方法是：
1）使用HttpHandler（一般处理程序）绘制随机验证码的图，以及产生随机码，并输出到页面的OutputStream中。
2）页面中使用异步方式（js等）进行刷新当前页面的验证码。
【示例】
1）创建一个“一般应用处理程序ashx”，代码如下：
[C#]
public class ValidationCode : IHttpHandler { //随机发生器 static Random r = new Random(Guid.NewGuid().GetHashCode()); //排除黑色、透明色颜色，因为底色黑色 static PropertyInfo[] colors = (typeof(Brushes).GetProperties(System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.GetProperty | System.Reflection.BindingFlags.Static)).Where(p => p.Name != "Black" && p.Name != "Transparent").Select(p => p).ToArray(); //排除黑色颜色，因为底色黑色 static PropertyInfo[] linecolors = (typeof(Pens).GetProperties(System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.GetProperty | System.Reflection.BindingFlags.Static)).Where(p => p.Name != "Black").Select(p => p).ToArray(); //获取静态类Brushes实例对象 static object colorobj = typeof(Brushes).GetConstructor(BindingFlags.NonPublic, null, Type.EmptyTypes, null); //获取静态类Pens实例对象 static object penobj = typeof(Pens).GetConstructor(BindingFlags.NonPublic, null, Type.EmptyTypes, null); //每个随机字符的宽度 const float PERNUMBERWIDTH = 40.0f; //每个字符的高度 const float PERNUMBERHEIGHT = 50.0f; public void ProcessRequest(HttpContext context) { //获取要产生多少随机数（默认产生5个） int reqNum = 5; if (context.Request.QueryString["reqNum"] != null) { int.TryParse(context.Request.QueryString["reqNum"], out reqNum); } //产生多少大的背景图 Bitmap bt = new Bitmap((int)(PERNUMBERWIDTH*reqNum), (int)PERNUMBERHEIGHT); Graphics g = Graphics.FromImage(bt); //产生4个随机数（number可以被保存到Session中） string numbers = ""; //绘制数字 for (int i = 1; i <= reqNum; i++) { numbers += r.Next(0, 9).ToString(); var color = (PropertyInfo)colors.GetValue(r.Next(0, colors.Length)); context.Response.Write(color.Name + "<br/>"); Brush randomcolor = (Brush)color.GetValue(colorobj, null); g.DrawString(numbers[i-1].ToString(), new Font("黑体", PERNUMBERWIDTH),randomcolor, new PointF((i-1)*PERNUMBERWIDTH, 0f)); } //绘制随机线条 int linenum = r.Next(10, 21); for (int i = 1; i <= linenum; i++) { var linecolor = (PropertyInfo)linecolors.GetValue(r.Next(0, colors.Length)); Pen randomcolor = (Pen)linecolor.GetValue(penobj, null); g.DrawLine(randomcolor, new PointF((float)(r.NextDouble() * PERNUMBERWIDTH * reqNum), (float)(r.NextDouble() * PERNUMBERHEIGHT)), new PointF((float)(r.NextDouble() * PERNUMBERWIDTH * reqNum), (float)(r.NextDouble() * PERNUMBERHEIGHT))); } g.Dispose(); context.Response.Clear(); context.Response.ContentType = "image/jpeg"; bt.Save(context.Response.OutputStream, ImageFormat.Jpeg); bt.Dispose(); context.Response.End(); } public bool IsReusable { get { return false; } } }
[VB.NET]
Public Class ValidationCode Implements IHttpHandler '随机发生器 Shared r As New Random(Guid.NewGuid().GetHashCode()) '排除黑色、透明色颜色，因为底色黑色 Shared colors As PropertyInfo() = (GetType(Brushes).GetProperties(System.Reflection.BindingFlags.[Public] Or System.Reflection.BindingFlags.GetProperty Or System.Reflection.BindingFlags.[Static])).Where(Function(p) p.Name <> "Black" AndAlso p.Name <> "Transparent").[Select](Function(p) p).ToArray() '排除黑色颜色，因为底色黑色 Shared linecolors As PropertyInfo() = (GetType(Pens).GetProperties(System.Reflection.BindingFlags.[Public] Or System.Reflection.BindingFlags.GetProperty Or System.Reflection.BindingFlags.[Static])).Where(Function(p) p.Name <> "Black").[Select](Function(p) p).ToArray() '获取静态类Brushes实例对象 Shared colorobj As Object = GetType(Brushes).GetConstructor(BindingFlags.NonPublic, Nothing, Type.EmptyTypes, Nothing) '获取静态类Pens实例对象 Shared penobj As Object = GetType(Pens).GetConstructor(BindingFlags.NonPublic, Nothing, Type.EmptyTypes, Nothing) '每个随机字符的宽度 Const PERNUMBERWIDTH As Single = 40F '每个字符的高度 Const PERNUMBERHEIGHT As Single = 50F Public Sub ProcessRequest(context As HttpContext) '获取要产生多少随机数（默认产生5个） Dim reqNum As Integer = 5 If context.Request.QueryString("reqNum") IsNot Nothing Then Integer.TryParse(context.Request.QueryString("reqNum"), reqNum) End If '产生多少大的背景图 Dim bt As New Bitmap(CInt(Math.Truncate(PERNUMBERWIDTH * reqNum)), CInt(Math.Truncate(PERNUMBERHEIGHT))) Dim g As Graphics = Graphics.FromImage(bt) '产生4个随机数（number可以被保存到Session中） Dim numbers As String = "" '绘制数字 For i As Integer = 1 To reqNum numbers += r.[Next](0, 9).ToString() Dim color = DirectCast(colors.GetValue(r.[Next](0, colors.Length)), PropertyInfo) context.Response.Write(Convert.ToString(color.Name) & "<br/>") Dim randomcolor As Brush = DirectCast(color.GetValue(colorobj, Nothing), Brush) g.DrawString(numbers(i - 1).ToString(), New Font("黑体", PERNUMBERWIDTH), randomcolor, New PointF((i - 1) * PERNUMBERWIDTH, 0F)) Next '绘制随机线条 Dim linenum As Integer = r.[Next](10, 21) For i As Integer = 1 To linenum Dim linecolor = DirectCast(linecolors.GetValue(r.[Next](0, colors.Length)), PropertyInfo) Dim randomcolor As Pen = DirectCast(linecolor.GetValue(penobj, Nothing), Pen) g.DrawLine(randomcolor, New PointF(CSng(r.NextDouble() * PERNUMBERWIDTH * reqNum), CSng(r.NextDouble() * PERNUMBERHEIGHT)), New PointF(CSng(r.NextDouble() * PERNUMBERWIDTH * reqNum), CSng(r.NextDouble() * PERNUMBERHEIGHT))) Next g.Dispose() context.Response.Clear() context.Response.ContentType = "image/jpeg" bt.Save(context.Response.OutputStream, ImageFormat.Jpeg) bt.Dispose() context.Response.[End]() End Sub Public ReadOnly Property IsReusable() As Boolean Get Return False End Get End Property End Class
注意：
1）一些诸如Brushes等特定因为是公用的，需要通过反射获取全部的颜色属性列表，因此使用了静态变量，这样不必每次都初始化，节省内存和时间。
2）Brushes避免黑色和透明色（本示例背景色是黑色），Pens只需避免黑色即可。有关Brushes颜色，可以查阅：http://msdn.microsoft.com/zh-cn/library/system.windows.media.brush(v=vs.95).aspx
3）Bitmap类是用于绘制使用的，一般是空白的黑色背景。一般配合Image类+Graphics画布使用，进行绘制。
4）BitMap的Save方法有若干个重载版本，其中之一可以指定输出流以及设置图片格式。本示例就是使用了这个函数。
【应用】
Html中代码（验证码部分，局部）：
<h1> 验证码 </h1> <script> function ChangeSD() { document.getElementById("imgSD").src = ""; document.getElementById("imgSD").src = "/ValidationCode.ashx?reqNum=10"; }; </script> <img src="/ValidationCode.ashx?reqNum=10" id="imgSD" /> <input type="button" value="Change Validation Key" onclick="ChangeSD()" />
注意，之所以使用js设置img的src两次，是因为重复的路径不会引发请求。
