【转载】HttpContext.Cache和HttpRuntime.Cache

原文地址：HttpRuntime.Cache vs. HttpContext.Current.Cache  HttpContext.Cache和HttpRuntime.Cache   HttpContext.Current.Cache vs. HttpRuntime.Cache 

 

 

HttpRuntime.Cache vs. HttpContext.Current.Cache

Here's a development tip I came across on one of the ASP.NET discussion lists I'm on, at AspAdvice.com.

Original question:
Is there a difference in accessing the Cache of an application when calling HttpRuntime.Cache vs. HttpContext.Current.Cache?  I "think" I remember reading about a difference in the two a few years ago, but I don't remember the specifics.  This assumes that I am within a web application.

Answer from Rob Howard:
HttpRuntime.Cache is the recommended technique.

Calling the HttpContext does some additional look-ups as it has to resolve the current context relative to the running thread.

I use HttpContext.Current in a lot of the code I write too; but touching it as little as possible. Rather than calling HttpContext.Current repeatedly it's best to hang onto a reference and pass it around (when possible).

If you're in a component HttpRuntime.Cache is still the recommendation.

That said... the differences in performance are not going to be noticeable in 99% of the applications many of us write. The cases where it is going to matter is the 1% (or less) where you're trying to squeeze every last drop of performance out of you system. But this is a *minor* performance tweak, e.g. eliminating a database call, web service call or other out-of-process call in the application is definitely a better place to spend optimizing code.

For example, if you have 5 database calls in a particular code path reducing (or even optimizing) the queries is a much better use of time.

So yes, HttpRuntime.Cache is recommended but likely won't make a difference in most applications.

Another reply from James Shaw at CoverYourASP.NET:
I discovered another *great* reason to use HttpRuntime too, when writing my unit tests - HttpRuntime.Cache is always available, even in console apps like nunit!

http://www.coveryourasp.net/UnittestingandCaching

I never use HttpContext anymore, even in class libraries.

原文地址： HttpContext.Cache和HttpRuntime.Cache   HttpContext.Current.Cache vs. HttpRuntime.Cache 

 

Asp.Net中可以方便的使用缓存，对于Cache，一般有两种方式调用：HttpContext.Cache和HttpRuntime.Cache。那么这两种Cache有什么区别呢？

先来看看Msdn上的注释：
HttpRuntime.Cache：获取当前应用程序的 Cache。
HttpContext.Cache：为当前 HTTP 请求获取 Cache 对象。

那么是不是说对于HttpRuntime.Cache就是应用程序级，而HttpContext.Cache则是针对每个用户的呢？NO，而实际上，两者调用的是同一个对象。他们的区别仅仅在于调用方式不一样（就我所知）。

事实胜过雄辩，写个例子来证实一下（限于篇幅仅贴出关键代码，完整代码见附件WebDemo.rar）：

        /**//// <summary>
        /// 通过HttpRuntime.Cache的方式来保存Cache
        /// </summary>
        private void btnHttpRuntimeCacheSave_Click(object sender, System.EventArgs e)
        ...{
            HttpRuntime.Cache.Insert(cacheKey, cacheValue, null, DateTime.Now.AddMinutes(3), TimeSpan.Zero);
        }

        /**//// <summary>
        /// 通过HttpRuntime.Cache的方式来读取Cache
        /// </summary>
        private void btnHttpRuntimeCacheLoad_Click(object sender, System.EventArgs e)
        ...{
            if (HttpRuntime.Cache[cacheKey] == null)
            ...{
                cacheContent = "No Cache";
            }
            else
            ...{
                cacheContent = (string)HttpRuntime.Cache[cacheKey];
            }
            lblCacheContent.Text = cacheContent;
        }

        /**//// <summary>
        /// 通过HttpContext.Cache的方式来保存Cache
        /// </summary>
        private void btnHttpContextCacheSave_Click(object sender, System.EventArgs e)
        ...{
            HttpContext.Current.Cache.Insert(cacheKey, cacheValue, null, DateTime.Now.AddMinutes(3), TimeSpan.Zero);
        }

        /**//// <summary>
        /// 通过HttpContext.Cache的方式来读取Cache
        /// </summary>
        private void btnHttpContextCacheLoad_Click(object sender, System.EventArgs e)
        ...{
            if (HttpContext.Current.Cache[cacheKey] == null)
            ...{
                cacheContent = "No Cache";
            }
            else
            ...{
                cacheContent = (string)HttpContext.Current.Cache[cacheKey];
            }
            lblCacheContent.Text = cacheContent;
        }

通过这个例子可以很容易证明：
1. HttpContext.Cache保存的Cache，HttpContext.Cache和HttpRuntime.Cache都可以读取。
2. HttpRuntime.Cache保存的Cache，HttpContext.Cache和HttpRuntime.Cache都可以读取。
3. 无论是哪个用户通过什么方式对Cache的改变，其他用户无论用什么方式读取的Cache内容也会随之变。

原文地址：  HttpContext.Current.Cache vs. HttpRuntime.Cache 

.NET中Cache有两种调用方式：HttpContext.Current.Cache 和 HttpRuntime.Cache，这两种方式有什么区别呢？我们先看MSDN上的解释：
      HttpContext.Current.Cache：为当前 HTTP 请求获取Cache对象。
      HttpRuntime.Cache：获取当前应用程序的Cache。

      我们再用.NET Reflector工具看看HttpContext.Cache和HttpRuntime.Cache的实现：

HttpContext.Cache和HttpRuntime.Cache实现
    //System.Web.HttpContext.Cache属性实现
    public sealed class HttpContext
    {
        public Cache Cache
        {
            get
            {
                return HttpRuntime.Cache;
            }
        }
    }


    //System.Web.HttpRuntime.Cache属性实现
    public sealed class HttpRuntime
    {
        public static Cache Cache
        {
            get
            {
                if (AspInstallDirectoryInternal == null)
                {
                    throw new HttpException(SR.GetString("Aspnet_not_installed", new object[] { VersionInfo.SystemWebVersion }));
                }
                Cache cache = _theRuntime._cachePublic;
                if (cache == null)
                {
                    CacheInternal cacheInternal = CacheInternal;
                    CacheSection cacheSection = RuntimeConfig.GetAppConfig().Cache;
                    cacheInternal.ReadCacheInternalConfig(cacheSection);
                    _theRuntime._cachePublic = cacheInternal.CachePublic;
                    cache = _theRuntime._cachePublic;
                }
                return cache;
            }
        }
    }

       通过上面的代码我们可以看出：HttpContext.Current.Cache是调用HttpRuntime.Cache实现的，两者指向同一Cache对象。那么两者到底有没有区别的？既然两个指向的是同一Cache对象，两者的差别只能出现在HttpContext和HttpRuntime上了。我们再来看看MSDN中HttpContext和HttpRuntime的定义。
      HttpContext：封装有关个别HTTP请求的所有HTTP特定的信息，HttpContext.Current为当前的HTTP请求获取HttpContext对象。
      HttpRuntime：为当前应用程序提供一组ASP.NET运行时服务。

      由上面的定义可以看出：HttpRuntime.Cache相当于就是一个缓存具体实现类，这个类虽然被放在了System.Web命名空间下，但是非Web应用下也是可以使用；HttpContext.Current.Cache是对上述缓存类的封装，由于封装到了HttpContext类中，局限于只能在知道HttpContext下使用，即只能用于Web应用。

      下面的例子可以很好的说明这一点：

HttpContext.Cache和HttpRuntime.Cache的示例
    class CacheTest
    {
        static void Main(string[] args)
        {       
            System.Web.Caching.Cache httpRuntimeCache = System.Web.HttpRuntime.Cache;
            httpRuntimeCache.Insert("httpRuntimeCache", "I am stored in HttpRuntime.Cache");

            if (httpRuntimeCache != null)
            {
                Console.WriteLine("httpRuntimeCache:" + httpRuntimeCache["httpRuntimeCache"]);
            }

            System.Web.HttpContext httpContext = System.Web.HttpContext.Current;
            if (httpContext == null)
            {
                Console.WriteLine("HttpContext object is null in Console Project");
            }
            else
            {
                System.Web.Caching.Cache httpContextCache = httpContext.Cache;
                httpContextCache.Insert("httpContextCache", "I am stored in HttpRuntime.Cache");
                if (httpContextCache == null)
                {
                    Console.WriteLine("httpContextCache is null");
                }
            }
             
            Console.ReadLine();
        }
    }

      输出结果：httpRuntimeCache:I am stored in HttpRuntime.Cache
      HttpContext object is null in Console Project

      综上：我们在使用Cache时，尽量使用HttpRuntime.Cache，既能减少出错，也减少了一次函数调用。

      参考资料：HttpRuntime.Cache 与HttpContext.Current.Cache的疑问，HttpRuntime.Cache vs. HttpContext.Current.Cache