HttpRuntime.Cache

a.在Web开发中，我们经常能够使用到缓存对象(Cache),在ASP.NET中提供了两种缓存对象，HttpContext.Current.Cache和HttpRuntime.Cache,那么他们有什么区别呢？下面简单描述一下：

　　　　(1)：HttpContext.Current.Cache 为当前Http请求获取Cache对象，通俗来说就是由于此缓存封装在了HttpContenxt中，而HttpContext只局限于Web中，所以此缓存信息只能够在Web中使用。

　　　　(2)：HttpRuntime.Cache 获取当前应用程序的Cache，通俗来说就是此缓存信息虽然被放在了System.Web命名空间下，但是非Web程序也可以使用此缓存。

----------------------------------属性介绍-----------------------------------------------------------------------------------

//
???????// 摘要:
???????// ????向 System.Web.Caching.Cache 中插入具有依赖项和到期策略的对象。
???????//
???????// 参数:
???????// ??key:
???????// ????用于引用该对象的缓存键。
???????//
???????// ??value:
???????// ????要插入缓存中的对象。
???????//
???????// ??dependencies:
???????// ????所插入对象的文件依赖项或缓存键依赖项。 当任何依赖项更改时，该对象即无效，并从缓存中移除。 如果没有依赖项，则此参数包含 null。
???????//
???????// ??absoluteExpiration:
???????// ????所插入对象将到期并被从缓存中移除的时间。 要避免可能的本地时间问题（例如从标准时间改为夏时制），请使用 System.DateTime.UtcNow
???????// ????而不是 System.DateTime.Now 作为此参数值。 如果使用绝对到期，则 slidingExpiration 参数必须为 System.Web.Caching.Cache.NoSlidingExpiration。
???????//
???????// ??slidingExpiration:
???????// ????最后一次访问所插入对象时与该对象到期时之间的时间间隔。 如果该值等效于 20 分钟，则对象在最后一次被访问 20 分钟之后将到期并被从缓存中移除。
???????// ????如果使用可调到期，则 absoluteExpiration 参数必须为 System.Web.Caching.Cache.NoAbsoluteExpiration。
???????//
???????// 异常:
???????// ??System.ArgumentNullException:
???????// ????key 或 value 参数为 null。
???????//
???????// ??System.ArgumentOutOfRangeException:
???????// ????将 slidingExpiration 参数设置为小于 TimeSpan.Zero 或大于一年的等效值。
???????//
???????// ??System.ArgumentException:
???????// ????为要添加到 Cache 中的项设置 absoluteExpiration 和 slidingExpiration 参数。
???????public void Insert(string key, object value, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration);

--------------------公共类-------------------------------------------------------------------------------------------------------------------------------------------------

/// <summary>
???/// HttpRuntime Cache读取设置缓存信息封装
???/// 使用描述：给缓存赋值使用HttpRuntimeCache.Set(key,value....)等参数(第三个参数可以传递文件的路径(HttpContext.Current.Server.MapPath()))
???/// 读取缓存中的值使用JObject jObject=HttpRuntimeCache.Get(key) as JObject，读取到值之后就可以进行一系列判断
???/// </summary>
???public class HttpRuntimeCache
???{
???????/// <summary>
???????/// 设置缓存过期时间，可从配置文件中读取
???????/// </summary>
???????private static double Seconds = string.IsNullOrEmpty(ConfigurationManager.AppSettings["AbsoluteExpiration"]) ? 10 : Double.Parse(ConfigurationManager.AppSettings["AbsoluteExpiration"]);

???????/// <summary>
???????/// 缓存指定对象，设置缓存
???????/// </summary>
???????public static bool Set(string key, object value)
???????{
???????????return Set(key, value, null, DateTime.Now.AddSeconds(Seconds), Cache.NoSlidingExpiration, CacheItemPriority.Default, CachedItemRemoveCallBack);
???????}

???????/// <summary>
???????/// ?缓存指定对象，设置缓存
???????/// </summary>
???????public static bool Set(string key, object value, string path)
???????{
???????????try
???????????{
???????????????var cacheDependency = new CacheDependency(path);
???????????????return Set(key, value, cacheDependency);
???????????}
???????????catch
???????????{
???????????????return false;
???????????}
???????}

???????/// <summary>
???????/// 缓存指定对象，设置缓存
???????/// </summary>
???????public static bool Set(string key, object value, CacheDependency cacheDependency)
???????{
???????????return Set(key, value, cacheDependency, Cache.NoAbsoluteExpiration, Cache.NoSlidingExpiration,
???????????????CacheItemPriority.Default, null);
???????}

???????/// <summary>
???????/// 缓存指定对象，设置缓存
???????/// </summary>
???????public static bool Set(string key, object value, double seconds, bool isAbsulute)
???????{
???????????return Set(key, value, null, (isAbsulute ? DateTime.Now.AddSeconds(seconds) : Cache.NoAbsoluteExpiration),
???????????????(isAbsulute ? Cache.NoSlidingExpiration : TimeSpan.FromSeconds(seconds)), CacheItemPriority.Default, CachedItemRemoveCallBack);
???????}

???????/// <summary>
???????/// 获取缓存对象
???????/// </summary>
???????public static object Get(string key)
???????{
???????????return GetPrivate(key);
???????}

???????/// <summary>
???????/// 判断缓存中是否含有缓存该键
???????/// </summary>
???????public static bool Exists(string key)
???????{
???????????return (GetPrivate(key) != null);
???????}

???????/// <summary>
???????/// 移除缓存对象
???????/// </summary>
???????/// <param name="key"></param>
???????/// <returns></returns>
???????public static bool Remove(string key)
???????{
???????????if (string.IsNullOrEmpty(key))
???????????{
???????????????return false;
???????????}
???????????HttpRuntime.Cache.Remove(key);
???????????return true;
???????}

???????/// <summary>
???????/// 移除所有缓存
???????/// </summary>
???????/// <returns></returns>
???????public static bool RemoveAll()
???????{
???????????IDictionaryEnumerator iDictionaryEnumerator = HttpRuntime.Cache.GetEnumerator();
???????????while (iDictionaryEnumerator.MoveNext())
???????????{
???????????????HttpRuntime.Cache.Remove(Convert.ToString(iDictionaryEnumerator.Key));
???????????}
???????????return true;
???????}

???????//------------------------提供给上面方法进行调用-----------------------------------
???????/// <summary>
???????/// 设置缓存
???????/// </summary>
???????public static bool Set(string key, object value, CacheDependency cacheDependency, DateTime absoluteExpiration,
???????????TimeSpan slidingExpiration, CacheItemPriority cacheItemPriority, CacheItemRemovedCallback cacheItemRemovedCallback)
???????{
???????????if (string.IsNullOrEmpty(key) || value == null)
???????????{
???????????????return false;
???????????}
???????????HttpRuntime.Cache.Insert(key, value, cacheDependency, absoluteExpiration, slidingExpiration, cacheItemPriority,
???????????????cacheItemRemovedCallback);
???????????return true;
???????}

???????/// <summary>
???????/// 获取缓存
???????/// </summary>
???????private static object GetPrivate(string key)
???????{
???????????return string.IsNullOrEmpty(key) ? null : HttpRuntime.Cache.Get(key);
???????}
???????/// <summary>
???????/// 缓存到期后的回调函数,更新缓存
???????/// </summary>
???????/// <param name="key">缓存名称</param>
???????/// <param name="value">缓存的值</param>
???????/// <param name="reason">缓存到期的原因</param>
???????private static void CachedItemRemoveCallBack(string key, object value, CacheItemRemovedReason reason)
???????{
???????????if (!Exists(key))
???????????{
???????????????//更新缓存

???????????}
???????}
???}