Differences between different .net framework HtmlEncode methods - asp.net

Question

What differences, if any are there between:
System.Web.HttpUtility.HtmlEncode
System.Web.HttpServerUtility.HtmlEncode
System.Net.WebUtility.HtmlEncode
Both HttpUtility.HtmlEncode and HttpServerUtility.HtmlEncode say:
To encode or decode values outside of a web application, use the WebUtility class.
Which implies that there is a difference, but doesn't come out say so directly or say what the difference is, if there is one.

Answer 1

If you dig though the source code you can follow easily enough.
System.Web.HttpUtility.HtmlEncode
/// <devdoc>
/// <para>
/// HTML encodes a string and returns the encoded string.
/// </para>
/// </devdoc>
public static String HtmlEncode(String s) {
return HttpEncoder.Current.HtmlEncode(s);
}
System.Web.HttpServerUtility.HtmlEncode
/// <devdoc>
/// <para>
/// HTML
/// encodes a given string and
/// returns the encoded string.
/// </para>
/// </devdoc>
public string HtmlEncode(string s) {
return HttpUtility.HtmlEncode(s);
}
System.Net.WebUtility.HtmlEncode
public static string HtmlEncode(string value) {
if (String.IsNullOrEmpty(value)) {
return value;
}
// Don't create string writer if we don't have nothing to encode
int index = IndexOfHtmlEncodingChars(value, 0);
if (index == -1) {
return value;
}
StringWriter writer = new StringWriter(CultureInfo.InvariantCulture);
HtmlEncode(value, writer);
return writer.ToString();
}
So System.Web.HttpServerUtility.HtmlEncode actually uses System.Web.HttpUtility.HtmlEncode. If you drill into HttpEncoder.Current.HtmlEncode(s); this has the following code:
protected internal virtual void HtmlDecode(string value, TextWriter output) {
WebUtility.HtmlDecode(value, output);
}
Tl;Dr
So they all, ultimately, use System.Net.WebUtility.HtmlEncode. I guess the System.Web version are only there for backwards compatibillity. Hence the advice of using the System.Net version.