ASP.NET清空缓存时遇到的问题简析

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]); 
 } 

//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); 
} 

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 } ); 
 } 
}