[翻译]C#.我该如何分析和转换日期时间的到RFC 822的日期，时间格式(How do I parse and convert DateTi
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问：RFC822 日期-时间被很多应用到很多规范中，比如 RSS格式 ；在.NET中，我怎样将DateTime结构转换成等效RFC822日期时间格式
字符串展现，并且又能解析此字符串(string),重新用DateTime结构的呈现呢？
解决方法1：
DateTime today = DateTime.Now;
String rfc822 = today.ToString("r");
Console.WriteLine("RFC-822 date: 0", rfc822);
DateTime parsedRFC822 = DateTime.Parse(rfc822);
Console.WriteLine("Date: 0", parsedRFC822);
传入DateTime.toString()方法格式符号"r"实际上产生的是RFC1123规范格日期时间串，基于http://www.w3.org/Protocols/rfc822/#z28规范得知,当时传入RFC-822日期也是可以的。
我已经使用该方法创建了RSS源，并且通过了http://validator.w3.org/feed/check.cgi校验器的验证。
该方法的缺点是，在转换中他将日期时间转换成GMT格式的，要转回本地时间，您需要使用本地时区偏移量。为此，您可以使用TimeZone类获取当前时区偏移量，并将GMT替换成时区偏移量时间的字符串。
TimeZone tz = TimeZone.CurrentTimeZone;
String offset = tz.GetUtcOffset().ToString();
// My locale is Mountain time; offset is set to "-07:00:00"
// if local time is behind utc time, offset should start with "-".
// otherwise, add a plus sign to the beginning of the string.
if (!offset.StartsWith("-"))
offset = "+" + offset; // Add a (+) if its a UTC+ timezone
offset = offset.Substring(0,6); // only want the first 6 chars.
offset = offset.Replace(":", ""); // remove colons.
// offset now looks something like "-0700".
rfc822 = rfc822.Replace("GMT", offset);
// The rfc822 string can now be parsed back to a DateTime object,
// with the local time accounted for.
DateTime new
解决方法2：
这是 C# 中有关如何解析 DateTime 并将其转换为其 RFC-822 表示形式和转换日期时间的实现。
它唯一的限制是DateTime是UTC格式的。我承认这不是很优雅的代码，但他是能运行的。
/// <summary>
/// Provides methods for converting <see cref="DateTime"/> structures
/// to and from the equivalent <a href="http://www.w3.org/Protocols/rfc822/#z28">RFC 822</a>
/// string representation.
/// </summary>
public class Rfc822DateTime
//============================================================
// Private members
//============================================================
#region Private Members
/// <summary>
/// Private member to hold array of formats that RFC 822 date-time representations conform to.
/// </summary>
private static string[] formats = new string[0];
/// <summary>
/// Private member to hold the DateTime format string for representing a DateTime in the RFC 822 format.
/// </summary>
private const string format = "ddd, dd MMM yyyy HH:mm:ss K";
#endregion
//============================================================
// Public Properties
//============================================================
#region Rfc822DateTimeFormat
/// <summary>
/// Gets the custom format specifier that may be used to represent a <see cref="DateTime"/> in the RFC 822 format.
/// </summary>
/// <value>A <i>DateTime format string</i> that may be used to represent a <see cref="DateTime"/> in the RFC 822 format.</value>
/// <remarks>
/// <para>
/// This method returns a string representation of a <see cref="DateTime"/> that utilizes the time zone
/// offset (local differential) to represent the offset from Greenwich mean time in hours and minutes.
/// The <see cref="Rfc822DateTimeFormat"/> is a valid date-time format string for use
/// in the <see cref="DateTime.ToString(String, IFormatProvider)"/> method.
/// </para>
/// <para>
/// The <a href="http://www.w3.org/Protocols/rfc822/#z28">RFC 822</a> Date and Time specification
/// specifies that the year will be represented as a two-digit value, but the
/// <a href="http://www.rssboard.org/rss-profile#data-types-datetime">RSS Profile</a> recommends that
/// all date-time values should use a four-digit year. The <see cref="Rfc822DateTime"/> class
/// follows the RSS Profile recommendation when converting a <see cref="DateTime"/> to the equivalent
/// RFC 822 string representation.
/// </para>
/// </remarks>
public static string Rfc822DateTimeFormat
get
return format;
#endregion
#region Rfc822DateTimePatterns
/// <summary>
/// Gets an array of the expected formats for RFC 822 date-time string representations.
/// </summary>
/// <value>
/// An array of the expected formats for RFC 822 date-time string representations
/// that may used in the <see cref="DateTime.TryParseExact(String, string[], IFormatProvider, DateTimeStyles, out DateTime)"/> method.
/// </value>
/// <remarks>
/// The array of the expected formats that is returned assumes that the RFC 822 time zone
/// is represented as or converted to a local differential representation.
/// </remarks>
/// <seealso cref="ConvertZoneToLocalDifferential(String)"/>
public static string[] Rfc822DateTimePatterns
get
if (formats.Length > 0)
return formats;
else
formats = new string[35];
// two-digit day, four-digit year patterns
formats[0] = "ddd, dd MMM yyyy HH:mm:ss.fffffff zzzz";
formats[1] = "ddd, dd MMM yyyy HH:mm:ss.ffffff zzzz";
formats[2] = "ddd, dd MMM yyyy HH:mm:ss.fffff zzzz";
formats[3] = "ddd, dd MMM yyyy HH:mm:ss.ffff zzzz";
formats[4] = "ddd, dd MMM yyyy HH:mm:ss.fff zzzz";
formats[5] = "ddd, dd MMM yyyy HH:mm:ss.ff zzzz";
formats[6] = "ddd, dd MMM yyyy HH:mm:ss.f zzzz";
formats[7] = "ddd, dd MMM yyyy HH:mm:ss zzzz";
// two-digit day, two-digit year patterns
formats[8] = "ddd, dd MMM yy HH:mm:ss.fffffff zzzz";
formats[9] = "ddd, dd MMM yy HH:mm:ss.ffffff zzzz";
formats[10] = "ddd, dd MMM yy HH:mm:ss.fffff zzzz";
formats[11] = "ddd, dd MMM yy HH:mm:ss.ffff zzzz";
formats[12] = "ddd, dd MMM yy HH:mm:ss.fff zzzz";
formats[13] = "ddd, dd MMM yy HH:mm:ss.ff zzzz";
formats[14] = "ddd, dd MMM yy HH:mm:ss.f zzzz";
formats[15] = "ddd, dd MMM yy HH:mm:ss zzzz";
// one-digit day, four-digit year patterns
formats[16] = "ddd, d MMM yyyy HH:mm:ss.fffffff zzzz";
formats[17] = "ddd, d MMM yyyy HH:mm:ss.ffffff zzzz";
formats[18] = "ddd, d MMM yyyy HH:mm:ss.fffff zzzz";
formats[19] = "ddd, d MMM yyyy HH:mm:ss.ffff zzzz";
formats[20] = "ddd, d MMM yyyy HH:mm:ss.fff zzzz";
formats[21] = "ddd, d MMM yyyy HH:mm:ss.ff zzzz";
formats[22] = "ddd, d MMM yyyy HH:mm:ss.f zzzz";
formats[23] = "ddd, d MMM yyyy HH:mm:ss zzzz";
// two-digit day, two-digit year patterns
formats[24] = "ddd, d MMM yy HH:mm:ss.fffffff zzzz";
formats[25] = "ddd, d MMM yy HH:mm:ss.ffffff zzzz";
formats[26] = "ddd, d MMM yy HH:mm:ss.fffff zzzz";
formats[27] = "ddd, d MMM yy HH:mm:ss.ffff zzzz";
formats[28] = "ddd, d MMM yy HH:mm:ss.fff zzzz";
formats[29] = "ddd, d MMM yy HH:mm:ss.ff zzzz";
formats[30] = "ddd, d MMM yy HH:mm:ss.f zzzz";
formats[31] = "ddd, d MMM yy HH:mm:ss zzzz";
// Fall back patterns
formats[32] = "yyyy-MM-ddTHH:mm:ss.fffffffK"; // RoundtripDateTimePattern
formats[33] = DateTimeFormatInfo.InvariantInfo.UniversalSortableDateTimePattern;
formats[34] = DateTimeFormatInfo.InvariantInfo.SortableDateTimePattern;
return formats;
#endregion
//============================================================
// Public Methods
//============================================================
#region Parse(string s)
/// <summary>
/// Converts the specified string representation of a date and time to its <see cref="DateTime"/> equivalent.
/// </summary>
/// <param name="s">A string containing a date and time to convert.</param>
/// <returns>
/// A <see cref="DateTime"/> equivalent to the date and time contained in <paramref name="s"/>,
/// expressed as <i>Coordinated Universal Time (UTC)</i>.
/// </returns>
/// <remarks>
/// The string <paramref name="s"/> is parsed using formatting information in the <see cref="DateTimeFormatInfo.InvariantInfo"/> object.
/// </remarks>
/// <exception cref="ArgumentNullException"><paramref name="s"/> is a <b>null</b> reference (Nothing in Visual Basic).</exception>
/// <exception cref="ArgumentNullException"><paramref name="s"/> is an empty string.</exception>
/// <exception cref="FormatException"><paramref name="s"/> does not contain a valid RFC 822 string representation of a date and time.</exception>
public static DateTime Parse(string s)
//------------------------------------------------------------
// Validate parameter
//------------------------------------------------------------
if (String.IsNullOrEmpty(s))
throw new ArgumentNullException("s");
DateTime result;
if (Rfc822DateTime.TryParse(s, out result))
return result;
else
throw new FormatException(String.Format(null, "0 is not a valid RFC 822 string representation of a date and time.", s));
#endregion
#region ConvertZoneToLocalDifferential(string s)
/// <summary>
/// Converts the time zone component of an RFC 822 date and time string representation to its local differential (time zone offset).
/// </summary>
/// <param name="s">A string containing an RFC 822 date and time to convert.</param>
/// <returns>A date and time string that uses local differential to describe the time zone equivalent to the date and time contained in <paramref name="s"/>.</returns>
/// <exception cref="ArgumentNullException"><paramref name="s"/> is a <b>null</b> reference (Nothing in Visual Basic).</exception>
/// <exception cref="ArgumentNullException"><paramref name="s"/> is an empty string.</exception>
public static string ConvertZoneToLocalDifferential(string s)
string zoneRepresentedAsLocalDifferential = String.Empty;
//------------------------------------------------------------
// Validate parameter
//------------------------------------------------------------
if (String.IsNullOrEmpty(s))
throw new ArgumentNullException("s");
if(s.EndsWith(" UT", StringComparison.OrdinalIgnoreCase))
zoneRepresentedAsLocalDifferential = String.Concat(s.Substring(0, (s.LastIndexOf(" UT") + 1) ), "+00:00");
else if (s.EndsWith(" GMT", StringComparison.OrdinalIgnoreCase))
zoneRepresentedAsLocalDifferential = String.Concat(s.Substring(0, (s.LastIndexOf(" GMT") + 1 ) ), "+00:00");
else if (s.EndsWith(" EST", StringComparison.OrdinalIgnoreCase))
zoneRepresentedAsLocalDifferential = String.Concat(s.Substring(0, (s.LastIndexOf(" EST") + 1)), "-05:00");
else if (s.EndsWith(" EDT", StringComparison.OrdinalIgnoreCase))
zoneRepresentedAsLocalDifferential = String.Concat(s.Substring(0, (s.LastIndexOf(" EDT") + 1)), "-04:00");
else if (s.EndsWith(" CST", StringComparison.OrdinalIgnoreCase))
zoneRepresentedAsLocalDifferential = String.Concat(s.Substring(0, (s.LastIndexOf(" CST") + 1)), "-06:00");
else if (s.EndsWith(" CDT", StringComparison.OrdinalIgnoreCase))
zoneRepresentedAsLocalDifferential = String.Concat(s.Substring(0, (s.LastIndexOf(" CDT") + 1)), "-05:00");
else if (s.EndsWith(" MST", StringComparison.OrdinalIgnoreCase))
zoneRepresentedAsLocalDifferential = String.Concat(s.Substring(0, (s.LastIndexOf(" MST") + 1)), "-07:00");
else if (s.EndsWith(" MDT", StringComparison.OrdinalIgnoreCase))
zoneRepresentedAsLocalDifferential = String.Concat(s.Substring(0, (s.LastIndexOf(" MDT") + 1)), "-06:00");
else if (s.EndsWith(" PST", StringComparison.OrdinalIgnoreCase))
zoneRepresentedAsLocalDifferential = String.Concat(s.Substring(0, (s.LastIndexOf(" PST") + 1)), "-08:00");
else if (s.EndsWith(" PDT", StringComparison.OrdinalIgnoreCase))
zoneRepresentedAsLocalDifferential = String.Concat(s.Substring(0, (s.LastIndexOf(" PDT") + 1)), "-07:00");
else if (s.EndsWith(" Z", StringComparison.OrdinalIgnoreCase))
zoneRepresentedAsLocalDifferential = String.Concat(s.Substring(0, (s.LastIndexOf(" Z") + 1)), "+00:00");
else if (s.EndsWith(" A", StringComparison.OrdinalIgnoreCase))
zoneRepresentedAsLocalDifferential = String.Concat(s.Substring(0, (s.LastIndexOf(" A") + 1)), "-01:00");
else if (s.EndsWith(" M", StringComparison.OrdinalIgnoreCase))
zoneRepresentedAsLocalDifferential = String.Concat(s.Substring(0, (s.LastIndexOf(" M") + 1)), "-12:00");
else if (s.EndsWith(" N", StringComparison.OrdinalIgnoreCase))
zoneRepresentedAsLocalDifferential = String.Concat(s.Substring(0, (s.LastIndexOf(" N") + 1)), "+01:00");
else if (s.EndsWith(" Y", StringComparison.OrdinalIgnoreCase))
zoneRepresentedAsLocalDifferential = String.Concat(s.Substring(0, (s.LastIndexOf(" Y") + 1)), "+12:00");
else
zoneRepresentedAsLocalDifferential = s;
return zoneRepresentedAsLocalDifferential;
#endregion
#region ToString(DateTime utcDateTime)
/// <summary>
/// Converts the value of the specified <see cref="DateTime"/> object to its equivalent string representation.
/// </summary>
/// <param name="utcDateTime">The Coordinated Universal Time (UTC) <see cref="DateTime"/> to convert.</param>
/// <returns>A RFC 822 string representation of the value of the <paramref name="utcDateTime"/>.</returns>
/// <exception cref="ArgumentException">The specified <paramref name="utcDateTime"/> object does not represent a <see cref="DateTimeKind.Utc">Coordinated Universal Time (UTC)</see> value.</exception>
public static string ToString(DateTime utcDateTime)
if (utcDateTime.Kind != DateTimeKind.Utc)
throw new ArgumentException("utcDateTime");
return utcDateTime.ToString(Rfc822DateTime.Rfc822DateTimeFormat, DateTimeFormatInfo.InvariantInfo);
#endregion
#region TryParse(string s, out DateTime result)
/// <summary>
/// Converts the specified string representation of a date and time to its <see cref="DateTime"/> equivalent.
/// </summary>
/// <param name="s">A string containing a date and time to convert.</param>
/// <param name="result">
/// When this method returns, contains the <see cref="DateTime"/> value equivalent to the date and time
/// contained in <paramref name="s"/>, expressed as <i>Coordinated Universal Time (UTC)</i>,
/// if the conversion succeeded, or <see cref="DateTime.MinValue">MinValue</see> if the conversion failed.
/// The conversion fails if the s parameter is a <b>null</b> reference (Nothing in Visual Basic),
/// or does not contain a valid string representation of a date and time.
/// This parameter is passed uninitialized.
/// </param>
/// <returns><b>true</b> if the <paramref name="s"/> parameter was converted successfully; otherwise, <b>false</b>.</returns>
/// <remarks>
/// The string <paramref name="s"/> is parsed using formatting information in the <see cref="DateTimeFormatInfo.InvariantInfo"/> object.
/// </remarks>
public static bool TryParse(string s, out DateTime result)
//------------------------------------------------------------
// Attempt to convert string representation
//------------------------------------------------------------
bool wasConverted = false;
result = DateTime.MinValue;
if (!String.IsNullOrEmpty(s))
DateTime parseResult;
if (DateTime.TryParseExact(Rfc822DateTime.ConvertZoneToLocalDifferential(s), Rfc822DateTime.Rfc822DateTimePatterns, DateTimeFormatInfo.InvariantInfo, DateTimeStyles.AdjustToUniversal, out parseResult))
result = DateTime.SpecifyKind(parseResult, DateTimeKind.Utc);
wasConverted = true;
return wasConverted;
#endregion
评论：RFC822日期规范中，天和秒是可选的，以上代码没有处理。
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