介绍
本文将介绍如何在asp.net web api中利用过滤器属性实现缓存。
实现过程
1,首先在web.config文件下appsettings下定义“CacheEnabled”和“CacheTimespan”两个属性，
CacheEnabled属性决定是否启用缓存
CacheTimespan决定缓存过期时间戳
如下代码所示：
<appSettings>
<!--<add key="webpages:Version" value="2.0.0.0" />
<add key="webpages:Enabled" value="false" />
<add key="PreserveLoginUrl" value="true" />
<add key="ClientValidationEnabled" value="true" />
<add key="UnobtrusiveJavaScriptEnabled" value="true" />-->
<add key="CacheEnabled" value="true"/>
<add key="CacheTimespan" value="12000"/>
</appSettings>
2，添加WebApiOutputCacheAttribute类并继承ActionFilterAttribute ，需要添加引用：
using System.Net.Http;
using System.Web.Configuration;
using System.Net.Http.Headers;
using System.Net.Http.Formatting;
代码相当简单和直白，就是在get方法执行前判断缓存key存在不存在，如果存在读取value,并输出，在过滤器执行完后更新缓存,如果不存在刚直接调用api中get方法，输出结果。
public class WebApiOutputCacheAttribute :System.Web.Http.Filters.ActionFilterAttribute
{
// cache length in seconds
private int _timespan;
// true to enable cache
private bool _cacheEnabled = false;
// true if the cache depends on the caller user
private readonly bool _dependsOnIdentity;
// cache repository
private static readonly ObjectCache WebApiCache = MemoryCache.Default;
//private readonly SecurityHelper _securityHelper;
private readonly bool _invalidateCache; /// <summary>
/// Constructor
/// </summary>
public WebApiOutputCacheAttribute()
: this(true)
{
} /// <summary>
/// Constructor
/// </summary>
/// <param name="dependsOnIdentity"></param>
public WebApiOutputCacheAttribute(bool dependsOnIdentity)
: this(dependsOnIdentity, false)
{
} /// <summary>
/// Constructor
/// </summary>
/// <param name="dependsOnIdentity"></param>
/// <param name="invalidateCache">true to invalidate cache object</param>
public WebApiOutputCacheAttribute(bool dependsOnIdentity, bool invalidateCache)
{
//_securityHelper = new SecurityHelper();
_dependsOnIdentity = dependsOnIdentity;
_invalidateCache = invalidateCache; ReadConfig();
} /// <summary>
/// Called by the ASP.NET MVC framework before the action method executes.
/// </summary>
/// <param name="filterContext">The filter context.</param>
public override void OnActionExecuting(HttpActionContext filterContext)
{
if (_cacheEnabled)
{
if (filterContext != null)
{
if (IsCacheable(filterContext))
{
string _cachekey = string.Join(":", new string[]
{
filterContext.Request.RequestUri.OriginalString,
filterContext.Request.Headers.Accept.FirstOrDefault().ToString(),
}); //if (_dependsOnIdentity)
// _cachekey = _cachekey.Insert(0, _securityHelper.GetUser()); if (WebApiCache.Contains(_cachekey))
{
//TraceManager.TraceInfo(String.Format("Cache contains key: {0}", _cachekey)); var val = (string)WebApiCache.Get(_cachekey);
if (val != null)
{
filterContext.Response = filterContext.Request.CreateResponse();
filterContext.Response.Content = new StringContent(val);
var contenttype = (MediaTypeHeaderValue)WebApiCache.Get(_cachekey + ":response-ct");
if (contenttype == null)
contenttype = new MediaTypeHeaderValue(_cachekey.Split(':')[1]);
filterContext.Response.Content.Headers.ContentType = contenttype;
return;
}
}
}
}
else
{
throw new ArgumentNullException("actionContext");
}
}
} /// <summary>
/// Called by the ASP.NET MVC framework after the action method executes.
/// </summary>
/// <param name="filterContext">The filter context.</param>
public override void OnActionExecuted(HttpActionExecutedContext filterContext)
{
try
{
if (_cacheEnabled)
{
if (WebApiCache != null)
{
string _cachekey = string.Join(":", new string[]
{
filterContext.Request.RequestUri.OriginalString,
filterContext.Request.Headers.Accept.FirstOrDefault().ToString(),
}); //if (_dependsOnIdentity)
// _cachekey = _cachekey.Insert(0, _securityHelper.GetUser()); if (filterContext.Response != null && filterContext.Response.Content != null)
{
string body = filterContext.Response.Content.ReadAsStringAsync().Result; if (WebApiCache.Contains(_cachekey))
{
WebApiCache.Set(_cachekey, body, DateTime.Now.AddSeconds(_timespan));
WebApiCache.Set(_cachekey + ":response-ct", filterContext.Response.Content.Headers.ContentType, DateTime.Now.AddSeconds(_timespan));
}
else
{
WebApiCache.Add(_cachekey, body, DateTime.Now.AddSeconds(_timespan));
WebApiCache.Add(_cachekey + ":response-ct", filterContext.Response.Content.Headers.ContentType, DateTime.Now.AddSeconds(_timespan));
}
}
}
} if (_invalidateCache)
{
CleanCache();
}
}
catch (Exception ex)
{
//TraceManager.TraceError(ex);
}
} /// <summary>
/// Removes all items from the cache
/// </summary>
private static void CleanCache()
{
if (WebApiCache != null)
{
List<string> keyList = WebApiCache.Select(w => w.Key).ToList();
foreach (string key in keyList)
{
WebApiCache.Remove(key);
}
}
} private void ReadConfig()
{
if (!Boolean.TryParse(WebConfigurationManager.AppSettings["CacheEnabled"], out _cacheEnabled))
_cacheEnabled = false; if (!Int32.TryParse(WebConfigurationManager.AppSettings["CacheTimespan"], out _timespan))
_timespan = 1800; // seconds
} private bool IsCacheable(HttpActionContext ac)
{
if (_timespan > 0)
{
if (ac.Request.Method == HttpMethod.Get)
return true;
}
else
{
throw new InvalidOperationException("Wrong Arguments");
}
return false;
}
}
在api中：
// GET api/values/5
[WebApiOutputCacheAttribute(true)]
public string Get(int id)
{
return DateTime.Now.ToString();
}