OutputCacheProvider OutputCache的一点点认识

在asp.net4.0后我们可以实现自己的OutputCacheProvider来控制缓存的位置了，但是我发现很多人多OutputCacheProvider的调用并不是很清楚。首先我们要知道缓存是在哪里注册的。答案是OutputCacheModule

void IHttpModule.Init(HttpApplication app)
{
if (RuntimeConfig.GetAppConfig().OutputCache.EnableOutputCache)
{
app.ResolveRequestCache += new EventHandler(this.OnEnter);
app.UpdateRequestCache += new EventHandler(this.OnLeave);
}
}

(RuntimeConfig.GetAppConfig().OutputCache.EnableOutputCache这句很明白检查我们的配置，看看你是否启用缓存。OnEnter是在处理前读取缓存数据，处理后设置缓存。

那么先让我们看看OnEnter的方法把，我把里面多数代码删除只留主要的结果。

internal void OnEnter(object source, EventArgs eventArgs)
{
this._key = null;
string str;

       HttpResponse response = context.Response;
this._key = str = this.CreateOutputCachedItemKey(context, null);
object obj2 = OutputCache.Get(str);
if (obj2 != null)
{
CachedVary cachedVary = obj2 as CachedVary;
             if (cachedVary != null)
{
str = this.CreateOutputCachedItemKey(context, cachedVary);
obj2 = OutputCache.Get(str);}

      CachedRawResponse response2 = (CachedRawResponse) obj2;
                    HttpCachePolicySettings settings = response2._settings;
                HttpRawResponse rawResponse = response2._rawResponse;
                  response.UseSnapshot(rawResponse, sendBody);

application.CompleteRequest();
return;
}
return;
}
}

这里有两次调用obj2 = OutputCache.Get(str)，我们来分析一下吧，第一次取出来的数据被转化为cachedVary，这个东西就是保存我们OutputCache中的那些属性配置的一个实例，所以OutputCache不同的属性就会产生不同的cachedVary值，而第二次读取的obj2才是我们真正需要保存的东西，把它取到后做一系列的处理最后结束此次http请求。

如取值是取2次那么设置也一定是设置2次了。

internal void OnLeave(object source, EventArgs eventArgs)
{

CachedVary vary;
string str;
vary = new CachedVary(varyByContentEncodings, varyByHeaders, varyByParams, varyByAllParams, currentSettings.VaryByCustom);
    str = this.CreateOutputCachedItemKey(context, vary);

HttpRawResponse snapshot = response.GetSnapshot();
string kernelCacheUrl = response.SetupKernelCaching(null);
Guid cachedVaryId = (vary != null) ? vary.CachedVaryId : Guid.Empty;
CachedRawResponse rawResponse = new CachedRawResponse(snapshot, currentSettings, kernelCacheUrl, cachedVaryId);
CacheDependency dependencies = response.CreateCacheDependencyForResponse();
           OutputCache.InsertResponse(this._key, vary, str, rawResponse, dependencies, noAbsoluteExpiration, noSlidingExpiration);

}
}

在这里我们看到了CachedVary、CachedRawResponse的两个实例，在这里我们可以确定先前第二次调用obj2 = OutputCache.Get(str)的obj2应该是一个CachedRawResponse实例。而OutputCache的InsertResponse方法：

internal static void InsertResponse(string cachedVaryKey, CachedVary cachedVary, string rawResponseKey, CachedRawResponse rawResponse, CacheDependency dependencies, DateTime absExp, TimeSpan slidingExp)
{
OutputCacheProvider provider = GetProvider(HttpContext.Current);
provider.Set(cachedVaryKey, cachedVary, Cache.NoAbsoluteExpiration);
provider.Set(rawResponseKey, entry, absExp);
}

我相信大家看到这里就明白了，OutputCache的保存和读取都是操作2个实例，一个是OutputCache配置实例CachedVary ，另一个是真正的数据流CachedRawResponse 。

看到OutputCache的InsertResponse方法这里提到了OutputCacheProvider provider = GetProvider(HttpContext.Current)而在OutputCacheProvider 的Get方法中也调用了这句

internal static object Get(string key)
{
    object obj2 = null;
    OutputCacheProvider provider = GetProvider(HttpContext.Current);
    if (provider != null)
    {
        obj2 = provider.Get(key);
        OutputCacheEntry oce = obj2 as OutputCacheEntry;
        if (oce != null)
        {
            if (HasDependencyChanged(false, oce.DependenciesKey, oce.Dependencies, oce.KernelCacheUrl, key, provider.Name))
            {
                RemoveFromProvider(key, provider.Name);
                return null;
            }
            obj2 = Convert(oce);
        }
    }
    if (obj2 == null)
    {
        obj2 = HttpRuntime.CacheInternal.Get(key);
    }
    return obj2;
}

而OutputCache的GetProvider的方法干什么的我想我就不提了，相信大家都会明白。

所以要实现自定义的缓存，可以有两种方案分别是实现自己的OutputCacheProvider和注册自己OutputCacheModule

    public class MemoryCacheProvider : OutputCacheProvider
    { 
        public override object Add(string key, object entry, DateTime utcExpiry)
        {
            return null;
        }

        public override object Get(string key)
        {
            return null;
        }

        public override void Set(string key, object entry, DateTime utcExpiry)
        {
        }

        public override void Remove(string key)
        {
        }
    }
  
public class CustOutputCacheModule : IHttpModule
    {
        public void Dispose()
        {
        }

        public void Init(HttpApplication context)
        {
            context.ResolveRequestCache += new EventHandler(context_ResolveRequestCache);
            context.UpdateRequestCache += new EventHandler(context_UpdateRequestCache);
        }

        void context_UpdateRequestCache(object sender, EventArgs e)
        {  
        }

        void context_ResolveRequestCache(object sender, EventArgs e)
        {          
        }
    }

　　相应的配置是

posted on 2012-11-07 15:51 dz45693 阅读(3437) 评论(3) 编辑收藏举报

刷新页面返回顶部

dz45693

OutputCacheProvider OutputCache的一点点认识

导航

公告