asp.net 验证码的简单制作(vb.net+C#)

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() 
&#39;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() 
&#39;获取静态类Brushes实例对象 
Shared colorobj As Object = GetType(Brushes).GetConstructor(BindingFlags.NonPublic, Nothing, Type.EmptyTypes, Nothing) 
&#39;获取静态类Pens实例对象 
Shared penobj As Object = GetType(Pens).GetConstructor(BindingFlags.NonPublic, Nothing, Type.EmptyTypes, Nothing) 
&#39;每个随机字符的宽度 
Const PERNUMBERWIDTH As Single = 40F 
&#39;每个字符的高度 
Const PERNUMBERHEIGHT As Single = 50F 
Public Sub ProcessRequest(context As HttpContext) 
&#39;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 
&#39;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) 
&#39;产生4个随机数（number可以被保存到Session中） 
Dim numbers As String = "" 
&#39;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 
&#39;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。

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