一起谈.NET技术，浅析ASP.NET清空缓存时遇到的问题

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();
}

/// <summary>
/// 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 } );
}
}