src/ObjectRenderer/RendererMap.cs

#region Apache License
//
// Licensed to the Apache Software Foundation (ASF) under one or more 
// contributor license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright ownership. 
// The ASF licenses this file to you under the Apache License, Version 2.0
// (the "License"); you may not use this file except in compliance with 
// the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
#endregion

using System;
using System.IO;
#if NETSTANDARD1_3
using System.Reflection;
#endif

using log4net.Util;

namespace log4net.ObjectRenderer
{
	/// <summary>
	/// Map class objects to an <see cref="IObjectRenderer"/>.
	/// </summary>
	/// <remarks>
	/// <para>
	/// Maintains a mapping between types that require special
	/// rendering and the <see cref="IObjectRenderer"/> that
	/// is used to render them.
	/// </para>
	/// <para>
	/// The <see cref="M:FindAndRender(object)"/> method is used to render an
	/// <c>object</c> using the appropriate renderers defined in this map.
	/// </para>
	/// </remarks>
	/// <author>Nicko Cadell</author>
	/// <author>Gert Driesen</author>
	public class RendererMap
	{
        private readonly static Type declaringType = typeof(RendererMap);

		#region Member Variables

		private System.Collections.Hashtable m_map;
		private System.Collections.Hashtable m_cache = new System.Collections.Hashtable();

		private static IObjectRenderer s_defaultRenderer = new DefaultRenderer();

		#endregion

		#region Constructors

		/// <summary>
		/// Default Constructor
		/// </summary>
		/// <remarks>
		/// <para>
		/// Default constructor.
		/// </para>
		/// </remarks>
		public RendererMap() 
		{
			m_map = System.Collections.Hashtable.Synchronized(new System.Collections.Hashtable());
		}

		#endregion

		/// <summary>
		/// Render <paramref name="obj"/> using the appropriate renderer.
		/// </summary>
		/// <param name="obj">the object to render to a string</param>
		/// <returns>the object rendered as a string</returns>
		/// <remarks>
		/// <para>
		/// This is a convenience method used to render an object to a string.
		/// The alternative method <see cref="M:FindAndRender(object,TextWriter)"/>
		/// should be used when streaming output to a <see cref="TextWriter"/>.
		/// </para>
		/// </remarks>
		public string FindAndRender(object obj)
		{
			// Optimisation for strings
			string strData = obj as String;
			if (strData != null)
			{
				return strData;
			}

			StringWriter stringWriter = new StringWriter(System.Globalization.CultureInfo.InvariantCulture);
			FindAndRender(obj, stringWriter);
			return stringWriter.ToString();
		}

		/// <summary>
		/// Render <paramref name="obj"/> using the appropriate renderer.
		/// </summary>
		/// <param name="obj">the object to render to a string</param>
		/// <param name="writer">The writer to render to</param>
		/// <remarks>
		/// <para>
		/// Find the appropriate renderer for the type of the
		/// <paramref name="obj"/> parameter. This is accomplished by calling the
		/// <see cref="M:Get(Type)"/> method. Once a renderer is found, it is
		/// applied on the object <paramref name="obj"/> and the result is returned
		/// as a <see cref="string"/>.
		/// </para>
		/// </remarks>
		public void FindAndRender(object obj, TextWriter writer) 
		{
			if (obj == null)
			{
				writer.Write(SystemInfo.NullText);
			}
			else 
			{
				// Optimisation for strings
				string str = obj as string;
				if (str != null)
				{
					writer.Write(str);
				}
				else
				{
					// Lookup the renderer for the specific type
					try
					{
						Get(obj.GetType()).RenderObject(this, obj, writer);
					}
					catch(Exception ex)
					{
						// Exception rendering the object
						log4net.Util.LogLog.Error(declaringType, "Exception while rendering object of type ["+obj.GetType().FullName+"]", ex);

						// return default message
						string objectTypeName = "";
						if (obj != null && obj.GetType() != null)
						{
							objectTypeName = obj.GetType().FullName;
						}

						writer.Write("<log4net.Error>Exception rendering object type ["+objectTypeName+"]");
						if (ex != null)
						{
							string exceptionText = null;

							try
							{
								exceptionText = ex.ToString();
							}
							catch
							{
								// Ignore exception
							}

							writer.Write("<stackTrace>" + exceptionText + "</stackTrace>");
						}
						writer.Write("</log4net.Error>");
					}
				}
			}
		}

		/// <summary>
		/// Gets the renderer for the specified object type
		/// </summary>
		/// <param name="obj">the object to lookup the renderer for</param>
		/// <returns>the renderer for <paramref name="obj"/></returns>
		/// <remarks>
		/// <param>
		/// Gets the renderer for the specified object type.
		/// </param>
		/// <param>
		/// Syntactic sugar method that calls <see cref="M:Get(Type)"/> 
		/// with the type of the object parameter.
		/// </param>
		/// </remarks>
		public IObjectRenderer Get(Object obj) 
		{
			if (obj == null) 
			{
				return null;
			}
			else
			{
				return Get(obj.GetType());
			}
		}
  
		/// <summary>
		/// Gets the renderer for the specified type
		/// </summary>
		/// <param name="type">the type to lookup the renderer for</param>
		/// <returns>the renderer for the specified type</returns>
		/// <remarks>
		/// <para>
		/// Returns the renderer for the specified type.
		/// If no specific renderer has been defined the
		/// <see cref="DefaultRenderer"/> will be returned.
		/// </para>
		/// </remarks>
		public IObjectRenderer Get(Type type) 
		{
			if (type == null)
			{
				throw new ArgumentNullException("type");
			}

			IObjectRenderer result = null;

			// Check cache
			result = (IObjectRenderer)m_cache[type];

			if (result == null)
			{
#if NETSTANDARD1_3
				for (Type cur = type; cur != null; cur = cur.GetTypeInfo().BaseType)
#else
				for(Type cur = type; cur != null; cur = cur.BaseType)
#endif
				{
					// Search the type's interfaces
					result = SearchTypeAndInterfaces(cur);
					if (result != null)
					{
						break;
					}
				}

				// if not set then use the default renderer
				if (result == null)
				{
					result = s_defaultRenderer;
				}

				// Add to cache
				m_cache[type] = result;
			}

			return result;
		}  

		/// <summary>
		/// Internal function to recursively search interfaces
		/// </summary>
		/// <param name="type">the type to lookup the renderer for</param>
		/// <returns>the renderer for the specified type</returns>
		private IObjectRenderer SearchTypeAndInterfaces(Type type) 
		{
			IObjectRenderer r = (IObjectRenderer)m_map[type];
			if (r != null) 
			{
				return r;
			} 
			else 
			{
				foreach(Type t in type.GetInterfaces())
				{
					r = SearchTypeAndInterfaces(t);
					if (r != null)
					{
						return r; 
					}
				}
			}
			return null;
		}

		/// <summary>
		/// Get the default renderer instance
		/// </summary>
		/// <value>the default renderer</value>
		/// <remarks>
		/// <para>
		/// Get the default renderer
		/// </para>
		/// </remarks>
		public IObjectRenderer DefaultRenderer
		{
			get { return s_defaultRenderer; }
		}

		/// <summary>
		/// Clear the map of renderers
		/// </summary>
		/// <remarks>
		/// <para>
		/// Clear the custom renderers defined by using
		/// <see cref="Put"/>. The <see cref="DefaultRenderer"/>
		/// cannot be removed.
		/// </para>
		/// </remarks>
		public void Clear() 
		{
			m_map.Clear();
			m_cache.Clear();
		}

		/// <summary>
		/// Register an <see cref="IObjectRenderer"/> for <paramref name="typeToRender"/>. 
		/// </summary>
		/// <param name="typeToRender">the type that will be rendered by <paramref name="renderer"/></param>
		/// <param name="renderer">the renderer for <paramref name="typeToRender"/></param>
		/// <remarks>
		/// <para>
		/// Register an object renderer for a specific source type.
		/// This renderer will be returned from a call to <see cref="M:Get(Type)"/>
		/// specifying the same <paramref name="typeToRender"/> as an argument.
		/// </para>
		/// </remarks>
		public void Put(Type typeToRender, IObjectRenderer renderer) 
		{
			m_cache.Clear();

			if (typeToRender == null)
			{
				throw new ArgumentNullException("typeToRender");
			}
			if (renderer == null)
			{
				throw new ArgumentNullException("renderer");
			}

			m_map[typeToRender] = renderer;
		}	
	}
}