C# ICache.GetAsync方法代码示例

		public async Task<ResponseHandlerResult> HandleResponseAsync(HttpContextBase context, IResponse suggestedResponse, ICache cache, string cacheKey)
		{
			context.ThrowIfNull("context");
			suggestedResponse.ThrowIfNull("suggestedResponse");

			if (!suggestedResponse.CachePolicy.HasPolicy || cache == null || cacheKey == null)
			{
				return ResponseHandlerResult.ResponseNotHandled();
			}

			CacheItem cacheItem = await cache.GetAsync(cacheKey);
			string responseETag = suggestedResponse.CachePolicy.ETag;

			#region If-Match precondition header

			IfMatchHeader[] ifMatchHeaders = IfMatchHeader.ParseMany(context.Request.Headers["If-Match"]).ToArray();

			// Only consider If-Match headers if response status code is 2xx or 412
			if (ifMatchHeaders.Any() && ((suggestedResponse.StatusCode.StatusCode >= 200 && suggestedResponse.StatusCode.StatusCode <= 299) || suggestedResponse.StatusCode.StatusCode == 412))
			{
				// Return 412 if no If-Match header matches the response ETag
				// Return 412 if an "If-Match: *" header is present and the response has no ETag
				if (ifMatchHeaders.All(arg => arg.EntityTag.Value != responseETag) ||
				    (responseETag == null && ifMatchHeaders.Any(arg => arg.EntityTag.Value == "*")))
				{
					return await WriteResponseAsync(context.Response, new Response().PreconditionFailed());
				}
			}

			#endregion

			#region If-None-Match precondition header

			IfNoneMatchHeader[] ifNoneMatchHeaders = IfNoneMatchHeader.ParseMany(context.Request.Headers["If-None-Match"]).ToArray();

			if (ifNoneMatchHeaders.Any())
			{
				// Return 304 if an If-None-Match header matches the response ETag and the request method was GET or HEAD
				// Return 304 if an "If-None-Match: *" header is present, the response has an ETag and the request method was GET or HEAD
				// Return 412 if an "If-None-Match: *" header is present, the response has an ETag and the request method was not GET or HEAD
				if (ifNoneMatchHeaders.Any(arg => arg.EntityTag.Value == responseETag) ||
				    (ifNoneMatchHeaders.Any(arg => arg.EntityTag.Value == "*") && responseETag != null))
				{
					if (String.Equals(context.Request.HttpMethod, "GET", StringComparison.OrdinalIgnoreCase) || String.Equals(context.Request.HttpMethod, "HEAD", StringComparison.OrdinalIgnoreCase))
					{
						if (cacheItem != null)
						{
							cacheItem.Response.CachePolicy.Apply(context.Response.Cache);
						}
						else
						{
							suggestedResponse.CachePolicy.Apply(context.Response.Cache);
						}

						return await WriteResponseAsync(context.Response, new Response().NotModified());
					}

					return await WriteResponseAsync(context.Response, new Response().PreconditionFailed());
				}
			}

			#endregion

			#region If-Modified-Since precondition header

			IfModifiedSinceHeader ifModifiedSinceHeader = IfModifiedSinceHeader.Parse(context.Request.Headers["If-Modified-Since"]);
			bool validIfModifiedSinceHttpDate = ifModifiedSinceHeader != null && ifModifiedSinceHeader.HttpDate <= _systemClock.UtcDateTime;

			// Only consider an If-Modified-Since header if response status code is 200 and the HTTP-date is valid
			if (suggestedResponse.StatusCode.ParsedStatusCode == HttpStatusCode.OK && validIfModifiedSinceHttpDate)
			{
				// Return 304 if the response was cached before the HTTP-date
				if (cacheItem != null && cacheItem.CachedUtcTimestamp < ifModifiedSinceHeader.HttpDate)
				{
					return await WriteResponseAsync(context.Response, new Response().NotModified());
				}
			}

			#endregion

			#region If-Unmodified-Since precondition header

			IfUnmodifiedSinceHeader ifUnmodifiedSinceHeader = IfUnmodifiedSinceHeader.Parse(context.Request.Headers["If-Unmodified-Since"]);
			bool validIfUnmodifiedSinceHttpDate = ifUnmodifiedSinceHeader != null && ifUnmodifiedSinceHeader.HttpDate <= _systemClock.UtcDateTime;

			// Only consider an If-Unmodified-Since header if response status code is 2xx or 412 and the HTTP-date is valid
			if (((suggestedResponse.StatusCode.StatusCode >= 200 && suggestedResponse.StatusCode.StatusCode <= 299) || suggestedResponse.StatusCode.StatusCode == 412) && validIfUnmodifiedSinceHttpDate)
			{
				// Return 412 if the previous response was removed from the cache or was cached again at a later time
				if (cacheItem == null || cacheItem.CachedUtcTimestamp >= ifUnmodifiedSinceHeader.HttpDate)
				{
					return await WriteResponseAsync(context.Response, new Response().PreconditionFailed());
				}
			}

			#endregion

			#region No server caching

			// Do not cache the response when the response sends a non-cacheable status code, or when an Authorization header is present
//.........这里部分代码省略.........