私が取ったアプローチは、API コントローラー アクションから例外をスローし、例外を処理してアクション実行コンテキストに適切な応答を設定する例外フィルターを登録することです。
フィルターは、グローバル構成でフィルターを登録する前に、特定の種類の例外のハンドラーを登録する手段を提供する流暢なインターフェイスを公開します。
このフィルターを使用すると、例外処理をコントローラー アクション全体に分散させるのではなく、一元化された例外処理が可能になります。ただし、コントローラー アクション内で例外をキャッチし、その特定の例外の処理を一元化する意味がない場合は、特定の応答を返す場合があります。
フィルタの登録例：
GlobalConfiguration.Configuration.Filters.Add(
new UnhandledExceptionFilterAttribute()
.Register<KeyNotFoundException>(HttpStatusCode.NotFound)
.Register<SecurityException>(HttpStatusCode.Forbidden)
.Register<SqlException>(
(exception, request) =>
{
var sqlException = exception as SqlException;
if (sqlException.Number > 50000)
{
var response = request.CreateResponse(HttpStatusCode.BadRequest);
response.ReasonPhrase = sqlException.Message.Replace(Environment.NewLine, String.Empty);
return response;
}
else
{
return request.CreateResponse(HttpStatusCode.InternalServerError);
}
}
)
);
UnhandledExceptionFilterAttribute クラス:
using System;
using System.Collections.Concurrent;
using System.Net;
using System.Net.Http;
using System.Text;
using System.Web.Http.Filters;
namespace Sample
{
/// <summary>
/// Represents the an attribute that provides a filter for unhandled exceptions.
/// </summary>
public class UnhandledExceptionFilterAttribute : ExceptionFilterAttribute
{
#region UnhandledExceptionFilterAttribute()
/// <summary>
/// Initializes a new instance of the <see cref="UnhandledExceptionFilterAttribute"/> class.
/// </summary>
public UnhandledExceptionFilterAttribute() : base()
{
}
#endregion
#region DefaultHandler
/// <summary>
/// Gets a delegate method that returns an <see cref="HttpResponseMessage"/>
/// that describes the supplied exception.
/// </summary>
/// <value>
/// A <see cref="Func{Exception, HttpRequestMessage, HttpResponseMessage}"/> delegate method that returns
/// an <see cref="HttpResponseMessage"/> that describes the supplied exception.
/// </value>
private static Func<Exception, HttpRequestMessage, HttpResponseMessage> DefaultHandler = (exception, request) =>
{
if(exception == null)
{
return null;
}
var response = request.CreateResponse<string>(
HttpStatusCode.InternalServerError, GetContentOf(exception)
);
response.ReasonPhrase = exception.Message.Replace(Environment.NewLine, String.Empty);
return response;
};
#endregion
#region GetContentOf
/// <summary>
/// Gets a delegate method that extracts information from the specified exception.
/// </summary>
/// <value>
/// A <see cref="Func{Exception, String}"/> delegate method that extracts information
/// from the specified exception.
/// </value>
private static Func<Exception, string> GetContentOf = (exception) =>
{
if (exception == null)
{
return String.Empty;
}
var result = new StringBuilder();
result.AppendLine(exception.Message);
result.AppendLine();
Exception innerException = exception.InnerException;
while (innerException != null)
{
result.AppendLine(innerException.Message);
result.AppendLine();
innerException = innerException.InnerException;
}
#if DEBUG
result.AppendLine(exception.StackTrace);
#endif
return result.ToString();
};
#endregion
#region Handlers
/// <summary>
/// Gets the exception handlers registered with this filter.
/// </summary>
/// <value>
/// A <see cref="ConcurrentDictionary{Type, Tuple}"/> collection that contains
/// the exception handlers registered with this filter.
/// </value>
protected ConcurrentDictionary<Type, Tuple<HttpStatusCode?, Func<Exception, HttpRequestMessage, HttpResponseMessage>>> Handlers
{
get
{
return _filterHandlers;
}
}
private readonly ConcurrentDictionary<Type, Tuple<HttpStatusCode?, Func<Exception, HttpRequestMessage, HttpResponseMessage>>> _filterHandlers = new ConcurrentDictionary<Type, Tuple<HttpStatusCode?, Func<Exception, HttpRequestMessage, HttpResponseMessage>>>();
#endregion
#region OnException(HttpActionExecutedContext actionExecutedContext)
/// <summary>
/// Raises the exception event.
/// </summary>
/// <param name="actionExecutedContext">The context for the action.</param>
public override void OnException(HttpActionExecutedContext actionExecutedContext)
{
if(actionExecutedContext == null || actionExecutedContext.Exception == null)
{
return;
}
var type = actionExecutedContext.Exception.GetType();
Tuple<HttpStatusCode?, Func<Exception, HttpRequestMessage, HttpResponseMessage>> registration = null;
if (this.Handlers.TryGetValue(type, out registration))
{
var statusCode = registration.Item1;
var handler = registration.Item2;
var response = handler(
actionExecutedContext.Exception.GetBaseException(),
actionExecutedContext.Request
);
// Use registered status code if available
if (statusCode.HasValue)
{
response.StatusCode = statusCode.Value;
}
actionExecutedContext.Response = response;
}
else
{
// If no exception handler registered for the exception type, fallback to default handler
actionExecutedContext.Response = DefaultHandler(
actionExecutedContext.Exception.GetBaseException(), actionExecutedContext.Request
);
}
}
#endregion
#region Register<TException>(HttpStatusCode statusCode)
/// <summary>
/// Registers an exception handler that returns the specified status code for exceptions of type <typeparamref name="TException"/>.
/// </summary>
/// <typeparam name="TException">The type of exception to register a handler for.</typeparam>
/// <param name="statusCode">The HTTP status code to return for exceptions of type <typeparamref name="TException"/>.</param>
/// <returns>
/// This <see cref="UnhandledExceptionFilterAttribute"/> after the exception handler has been added.
/// </returns>
public UnhandledExceptionFilterAttribute Register<TException>(HttpStatusCode statusCode)
where TException : Exception
{
var type = typeof(TException);
var item = new Tuple<HttpStatusCode?, Func<Exception, HttpRequestMessage, HttpResponseMessage>>(
statusCode, DefaultHandler
);
if (!this.Handlers.TryAdd(type, item))
{
Tuple<HttpStatusCode?, Func<Exception, HttpRequestMessage, HttpResponseMessage>> oldItem = null;
if (this.Handlers.TryRemove(type, out oldItem))
{
this.Handlers.TryAdd(type, item);
}
}
return this;
}
#endregion
#region Register<TException>(Func<Exception, HttpRequestMessage, HttpResponseMessage> handler)
/// <summary>
/// Registers the specified exception <paramref name="handler"/> for exceptions of type <typeparamref name="TException"/>.
/// </summary>
/// <typeparam name="TException">The type of exception to register the <paramref name="handler"/> for.</typeparam>
/// <param name="handler">The exception handler responsible for exceptions of type <typeparamref name="TException"/>.</param>
/// <returns>
/// This <see cref="UnhandledExceptionFilterAttribute"/> after the exception <paramref name="handler"/>
/// has been added.
/// </returns>
/// <exception cref="ArgumentNullException">The <paramref name="handler"/> is <see langword="null"/>.</exception>
public UnhandledExceptionFilterAttribute Register<TException>(Func<Exception, HttpRequestMessage, HttpResponseMessage> handler)
where TException : Exception
{
if(handler == null)
{
throw new ArgumentNullException("handler");
}
var type = typeof(TException);
var item = new Tuple<HttpStatusCode?, Func<Exception, HttpRequestMessage, HttpResponseMessage>>(
null, handler
);
if (!this.Handlers.TryAdd(type, item))
{
Tuple<HttpStatusCode?, Func<Exception, HttpRequestMessage, HttpResponseMessage>> oldItem = null;
if (this.Handlers.TryRemove(type, out oldItem))
{
this.Handlers.TryAdd(type, item);
}
}
return this;
}
#endregion
#region Unregister<TException>()
/// <summary>
/// Unregisters the exception handler for exceptions of type <typeparamref name="TException"/>.
/// </summary>
/// <typeparam name="TException">The type of exception to unregister handlers for.</typeparam>
/// <returns>
/// This <see cref="UnhandledExceptionFilterAttribute"/> after the exception handler
/// for exceptions of type <typeparamref name="TException"/> has been removed.
/// </returns>
public UnhandledExceptionFilterAttribute Unregister<TException>()
where TException : Exception
{
Tuple<HttpStatusCode?, Func<Exception, HttpRequestMessage, HttpResponseMessage>> item = null;
this.Handlers.TryRemove(typeof(TException), out item);
return this;
}
#endregion
}
}
ソース コードもここにあります。