在网站中要做一个清理缓存的功能(也就是在缓存为到期之前就强制缓存过期),程序中有的地方使用的HttpRuntime.Cache来做的缓存,而和数据库交互部分则使用ObjectDataSource提供的缓存机制。清理HttpRuntime.Cache的缓存很简单,只要如下写就可以了。
- List<string> keys = new List<string>();
- // retrieve application Cache enumerator IDictionaryEnumerator enumerator = HttpRuntime.Cache.GetEnumerator();
- // copy all keys that currently exist in Cache
- while (enumerator.MoveNext()) {
- keys.Add(enumerator.Key.ToString());
- }
- // delete every key from cache
- for (int i = 0; i < keys.Count; i++)
- { HttpRuntime.Cache.Remove(keys[i]);
- }
本以为ObjectDataSource等数据源的缓存也是保存在HttpRuntime.Cache中,经过测试没想到竟然不是,因为执行上面的代码以后ObjectDataSource仍然是从缓存读取数据。
使用Reflector反编译发现ObjectDataSource是使用HttpRuntime.CacheInternal来实现的缓存,气氛呀,为什么微软总爱搞“特殊化”,对外提供一个Cache用,自己偷偷用CacheInternal做缓存。CacheInternal是internal 的,因此没法直接写代码调用,同时CacheInternal中也没提供清空缓存的方法,只能通过实验发现_caches._entries是保存缓存的 Hashtable,因此就用反射的方法调用CacheInternal,然后拿到_caches._entries,最后clear才算ok。
最终代码如下:
- //HttpRuntime下的CacheInternal属性(Internal的,内存中是CacheMulti类型)是ObjectDataSource等DataSource保存缓存的管理器
- //因为CacheInternal、_caches、_entries等都是internal或者private的,所以只能通过反射调用,而且可能会随着.Net升级而失效
- object cacheIntern = CommonHelper.GetPropertyValue(typeof(HttpRuntime), "CacheInternal") as IEnumerable;
- //_caches是CacheMulti中保存多CacheSingle的一个IEnumerable字段。
- IEnumerable _caches = CommonHelper.GetFieldValue(cacheIntern, "_caches") as IEnumerable; foreach (object cacheSingle in _caches) {
- ClearCacheInternal(cacheSingle);
- }
- private static void ClearCacheInternal(object cacheSingle)
- {
- //_entries是cacheSingle中保存缓存数据的一个private Hashtable
- Hashtable _entries = CommonHelper.GetFieldValue(cacheSingle, "_entries") as Hashtable;
- _entries.Clear();
- } mary>
- /// 得到type类型的静态属性propertyName的值
- /// </summary>
- /// <param name="type">
- </param>
- /// <param name="propertyName">
- </param>
- ///
- <returns>
- </returns>
- public static object GetPropertyValue(Type type, string propertyName)
- {
- foreach (PropertyInfo rInfo in type.GetProperties(BindingFlags.NonPublic | BindingFlags.Static | BindingFlags.Public | BindingFlags.Instance))
- {
- if (rInfo.Name == propertyName) {
- return rInfo.GetValue(null, new object[0]);
- }
- }
- throw new Exception("无法找到属性:" + propertyName);
- }
- /// <summary>
- /// 得到object对象的propertyName属性的值
- /// </summary>
- /// <param name="obj">
- </param>
- /// <param name="propertyName">
- </param>
- /// <returns>
- </returns>
- public static object GetPropertyValue(object obj, string propertyName)
- {
- Type type = obj.GetType();
- foreach (PropertyInfo rInfo in type.GetProperties(BindingFlags.NonPublic | BindingFlags.Static | BindingFlags.Public | BindingFlags.Instance))
- {
- if (rInfo.Name == propertyName) {
- return rInfo.GetValue(obj, new object[0]);
- }
- }
- throw new Exception("无法找到属性:" + propertyName);
- }
- public static object GetFieldValue(object obj, string fieldName)
- {
- Type type = obj.GetType();
- foreach (FieldInfo rInfo in type.GetFields(BindingFlags.NonPublic | BindingFlags.Static | BindingFlags.Public | BindingFlags.Instance))
- {
- if (rInfo.Name == fieldName) {
- return rInfo.GetValue(obj);
- }
- }
- throw new Exception("无法找到字段:" + fieldName);
- }
上面方法由于是通过crack的方法进行调用,可能有潜在的问题,因此仅供参考。
在google上搜索到另外一篇文章 http://www.msdnkk.hu/Articles/Clear_OutputCache-Minden_oldal_torlese ,由于是匈牙利文的,也看不懂在说什么,不过主干是代码,看他代码的思路和我一样,贴过来也供参考
- private void clearOutputCache()
- { Type ct = this.Cache.GetType();
- FieldInfo cif = ct.GetField( "_cacheInternal", BindingFlags.NonPublic | BindingFlags.Instance );
- Type cmt = Cache.GetType().Assembly.GetType( "System.Web.Caching.CacheMultiple" );
- Type cachekeyType = Cache.GetType().Assembly.GetType( "System.Web.Caching.CacheKey" );
- FieldInfo cachesfield = cmt.GetField( "_caches", BindingFlags.NonPublic | BindingFlags.Instance );
- object cacheInternal = cif.GetValue( this.Cache );
- object caches = cachesfield.GetValue( cacheInternal );
- Type arrayType = typeof( Array );
- MethodInfo arrayGetter = arrayType.GetMethod( "GetValue", new Type[] { typeof( int ) } );
- object cacheSingle = arrayGetter.Invoke( caches, new object[] { 1 } );
- FieldInfo entriesField = cacheSingle.GetType().GetField( "_entries", BindingFlags.Instance | BindingFlags.NonPublic );
- Hashtable entries = (Hashtable) entriesField.GetValue( cacheSingle );
- List<object> keys = new List<object>();
- foreach( object o in entries.Keys ) {
- keys.Add( o );
- }
- MethodInfo remove = cacheInternal.GetType().GetMethod( "Remove", BindingFlags.NonPublic | BindingFlags.Instance, null, new Type[] { cachekeyType, typeof( CacheItemRemovedReason )
- }, null );
- foreach( object key in keys )
- {
- remove.Invoke( cacheInternal, new object[] { key, CacheItemRemovedReason.Removed
- }
- );
- }
- }