optionconverter.cs

详细讲述了数据库编程

//				throw new InvalidOperationException("No type converter defined for [" + target + "]");
//			}
//			return converter;
//		}

		/// <summary>
		/// Checks if there is an appropriate type conversion from the source type to the target type.
		/// </summary>
		/// <param name="sourceType">The type to convert from.</param>
		/// <param name="targetType">The type to convert to.</param>
		/// <returns><c>true</c> if there is a conversion from the source type to the target type.</returns>
		/// <remarks>
		/// Checks if there is an appropriate type conversion from the source type to the target type.
		/// <para>
		/// </para>
		/// </remarks>
		public static bool CanConvertTypeTo(Type sourceType, Type targetType)
		{
			if (sourceType == null || targetType == null)
			{
				return false;
			}

			// Check if we can assign directly from the source type to the target type
			if (targetType.IsAssignableFrom(sourceType))
			{
				return true;
			}

			// Look for a To converter
			IConvertTo tcSource = ConverterRegistry.GetConvertTo(sourceType, targetType);
			if (tcSource != null)
			{
				if (tcSource.CanConvertTo(targetType))
				{
					return true;
				}
			}

			// Look for a From converter
			IConvertFrom tcTarget = ConverterRegistry.GetConvertFrom(targetType);
			if (tcTarget != null)
			{
				if (tcTarget.CanConvertFrom(sourceType))
				{
					return true;
				}
			}

			return false;
		}

		/// <summary>
		/// Converts an object to the target type.
		/// </summary>
		/// <param name="sourceInstance">The object to convert to the target type.</param>
		/// <param name="targetType">The type to convert to.</param>
		/// <returns>The converted object.</returns>
		/// <remarks>
		/// <para>
		/// Converts an object to the target type.
		/// </para>
		/// </remarks>
		public static object ConvertTypeTo(object sourceInstance, Type targetType)
		{
			Type sourceType = sourceInstance.GetType();

			// Check if we can assign directly from the source type to the target type
			if (targetType.IsAssignableFrom(sourceType))
			{
				return sourceInstance;
			}

			// Look for a TO converter
			IConvertTo tcSource = ConverterRegistry.GetConvertTo(sourceType, targetType);
			if (tcSource != null)
			{
				if (tcSource.CanConvertTo(targetType))
				{
					return tcSource.ConvertTo(sourceInstance, targetType);
				}
			}

			// Look for a FROM converter
			IConvertFrom tcTarget = ConverterRegistry.GetConvertFrom(targetType);
			if (tcTarget != null)
			{
				if (tcTarget.CanConvertFrom(sourceType))
				{
					return tcTarget.ConvertFrom(sourceInstance);
				}
			}

			throw new ArgumentException("Cannot convert source object [" + sourceInstance.ToString() + "] to target type [" + targetType.Name + "]", "sourceInstance");
		}

//		/// <summary>
//		/// Finds the value corresponding to <paramref name="key"/> in 
//		/// <paramref name="props"/> and then perform variable substitution 
//		/// on the found value.
//		/// </summary>
//		/// <param name="key">The key to lookup.</param>
//		/// <param name="props">The association to use for lookups.</param>
//		/// <returns>The substituted result.</returns>
//		public static string FindAndSubst(string key, System.Collections.IDictionary props) 
//		{
//			if (props == null)
//			{
//				throw new ArgumentNullException("props");
//			}
//
//			string v = props[key] as string;
//			if (v == null) 
//			{
//				return null;	  
//			}
//	
//			try 
//			{
//				return SubstituteVariables(v, props);
//			} 
//			catch(Exception e) 
//			{
//				LogLog.Error("OptionConverter: Bad option value [" + v + "].", e);
//				return v;
//			}	
//		}

		/// <summary>
		/// Instantiates an object given a class name.
		/// </summary>
		/// <param name="className">The fully qualified class name of the object to instantiate.</param>
		/// <param name="superClass">The class to which the new object should belong.</param>
		/// <param name="defaultValue">The object to return in case of non-fulfillment.</param>
		/// <returns>
		/// An instance of the <paramref name="className"/> or <paramref name="defaultValue"/>
		/// if the object could not be instantiated.
		/// </returns>
		/// <remarks>
		/// <para>
		/// Checks that the <paramref name="className"/> is a subclass of
		/// <paramref name="superClass"/>. If that test fails or the object could
		/// not be instantiated, then <paramref name="defaultValue"/> is returned.
		/// </para>
		/// </remarks>
		public static object InstantiateByClassName(string className, Type superClass, object defaultValue) 
		{
			if (className != null) 
			{
				try 
				{
					Type classObj = SystemInfo.GetTypeFromString(className, true, true);
					if (!superClass.IsAssignableFrom(classObj)) 
					{
						LogLog.Error("OptionConverter: A [" + className + "] object is not assignable to a [" + superClass.FullName + "] variable.");
						return defaultValue;	  
					}
					return Activator.CreateInstance(classObj);
				}
				catch (Exception e) 
				{
					LogLog.Error("OptionConverter: Could not instantiate class [" + className + "].", e);
				}
			}
			return defaultValue;	
		}

		/// <summary>
		/// Performs variable substitution in string <paramref name="val"/> from the 
		/// values of keys found in <paramref name="props"/>.
		/// </summary>
		/// <param name="value">The string on which variable substitution is performed.</param>
		/// <param name="props">The dictionary to use to lookup variables.</param>
		/// <returns>The result of the substitutions.</returns>
		/// <remarks>
		/// <para>
		/// The variable substitution delimiters are <b>${</b> and <b>}</b>.
		/// </para>
		/// <para>
		/// For example, if props contains <c>key=value</c>, then the call
		/// </para>
		/// <para>
		/// <code lang="C#">
		/// string s = OptionConverter.SubstituteVariables("Value of key is ${key}.");
		/// </code>
		/// </para>
		/// <para>
		/// will set the variable <c>s</c> to "Value of key is value.".
		/// </para>
		/// <para>
		/// If no value could be found for the specified key, then substitution 
		/// defaults to an empty string.
		/// </para>
		/// <para>
		/// For example, if system properties contains no value for the key
		/// "nonExistentKey", then the call
		/// </para>
		/// <para>
		/// <code lang="C#">
		/// string s = OptionConverter.SubstituteVariables("Value of nonExistentKey is [${nonExistentKey}]");
		/// </code>
		/// </para>
		/// <para>
		/// will set <s>s</s> to "Value of nonExistentKey is []".	 
		/// </para>
		/// <para>
		/// An Exception is thrown if <paramref name="value"/> contains a start 
		/// delimiter "${" which is not balanced by a stop delimiter "}". 
		/// </para>
		/// </remarks>
		public static string SubstituteVariables(string value, System.Collections.IDictionary props) 
		{
			StringBuilder buf = new StringBuilder();

			int i = 0;
			int j, k;
	
			while(true) 
			{
				j = value.IndexOf(DELIM_START, i);
				if (j == -1) 
				{
					if (i == 0)
					{
						return value;
					}
					else 
					{
						buf.Append(value.Substring(i, value.Length - i));
						return buf.ToString();
					}
				}
				else 
				{
					buf.Append(value.Substring(i, j - i));
					k = value.IndexOf(DELIM_STOP, j);
					if (k == -1) 
					{
						throw new LogException("[" + value + "] has no closing brace. Opening brace at position [" + j + "]");
					}
					else 
					{
						j += DELIM_START_LEN;
						string key = value.Substring(j, k - j);

						string replacement = props[key] as string;

						if (replacement != null) 
						{
							buf.Append(replacement);
						}
						i = k + DELIM_STOP_LEN;		
					}
				}
			}
		}

		#endregion Public Static Methods

		#region Private Static Methods

		/// <summary>
		/// Converts the string representation of the name or numeric value of one or 
		/// more enumerated constants to an equivalent enumerated object.
		/// </summary>
		/// <param name="enumType">The type to convert to.</param>
		/// <param name="value">The enum string value.</param>
		/// <param name="ignoreCase">If <c>true</c>, ignore case; otherwise, regard case.</param>
		/// <returns>An object of type <paramref name="enumType" /> whose value is represented by <paramref name="value" />.</returns>
		private static object ParseEnum(System.Type enumType, string value, bool ignoreCase) 
		{
#if !NETCF
			return Enum.Parse(enumType, value, ignoreCase);
#else
			FieldInfo[] fields = enumType.GetFields(BindingFlags.Public | BindingFlags.Static);

			string[] names = value.Split(new char[] {','});
			for (int i = 0; i < names.Length; ++i) 
			{
				names[i] = names [i].Trim();
			}

			long retVal = 0;

			try 
			{
				// Attempt to convert to numeric type
				return Enum.ToObject(enumType, Convert.ChangeType(value, typeof(long), CultureInfo.InvariantCulture));
			} 
			catch {}

			foreach (string name in names) 
			{
				bool found = false;
				foreach(FieldInfo field in fields) 
				{
					if (String.Compare(name, field.Name, ignoreCase) == 0) 
					{
						retVal |= ((IConvertible) field.GetValue(null)).ToInt64(CultureInfo.InvariantCulture);
						found = true;
						break;
					}
				}
				if (!found) 
				{
					throw new ArgumentException("Failed to lookup member [" + name + "] from Enum type [" + enumType.Name + "]");
				}
			}
			return Enum.ToObject(enumType, retVal);
#endif
		}		

		#endregion Private Static Methods

		#region Private Static Fields

		private const string DELIM_START = "${";
		private const char   DELIM_STOP  = '}';
		private const int DELIM_START_LEN = 2;
		private const int DELIM_STOP_LEN  = 1;

		#endregion Private Static Fields
	}
}