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
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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]);
}
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就可以了。
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。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:
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//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);
}
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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,主干是代码,代码的思路和我一样,贴过来也供参考。
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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 } );
}
}
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以上就是对ASP.NET清空缓存时遇到问题详细分析,为了让大家更好地解决此类问题,希望本文对大家的学习有所帮助。