如果您正在使用ASP.NET,可以使用Cache
类(System.Web.Caching
)。
这里有一个很好的辅助类:c-cache-helper-class
如果您指的是Windows窗体应用程序中的缓存,那取决于您尝试做什么以及在何处缓存数据。
我们已经针对某些方法实现了Web服务后面的缓存(使用System.Web.Caching
对象)。
但是,您可能还需要查看Caching Application Block。(请参见此处),它是.NET Framework 2.0的企业库的一部分。
MemoryCache是框架中一个不错的起点,但您也可以考虑使用开源库LazyCache,因为它具有比内存缓存更简单的API,并且具有内置锁定以及其他一些对开发人员友好的功能。它也可以在nuget上获得。
这里给您举个例子:
// Create our cache service using the defaults (Dependency injection ready).
// Uses MemoryCache.Default as default so cache is shared between instances
IAppCache cache = new CachingService();
// Declare (but don't execute) a func/delegate whose result we want to cache
Func<ComplexObjects> complexObjectFactory = () => methodThatTakesTimeOrResources();
// Get our ComplexObjects from the cache, or build them in the factory func
// and cache the results for next time under the given key
ComplexObject cachedResults = cache.GetOrAdd("uniqueKey", complexObjectFactory);
MemoryCache等存在一些限制:
您的工作负载将决定这些问题的严重程度。缓存的替代方法是限制缓存中对象的数量(而不是估算使用的内存)。然后,缓存替换策略确定在缓存已满时要丢弃哪个对象。
下面是一个简单缓存的源代码,采用最近最少使用的驱逐策略:
public sealed class ClassicLru<K, V>
{
private readonly int capacity;
private readonly ConcurrentDictionary<K, LinkedListNode<LruItem>> dictionary;
private readonly LinkedList<LruItem> linkedList = new LinkedList<LruItem>();
private long requestHitCount;
private long requestTotalCount;
public ClassicLru(int capacity)
: this(Defaults.ConcurrencyLevel, capacity, EqualityComparer<K>.Default)
{
}
public ClassicLru(int concurrencyLevel, int capacity, IEqualityComparer<K> comparer)
{
if (capacity < 3)
{
throw new ArgumentOutOfRangeException("Capacity must be greater than or equal to 3.");
}
if (comparer == null)
{
throw new ArgumentNullException(nameof(comparer));
}
this.capacity = capacity;
this.dictionary = new ConcurrentDictionary<K, LinkedListNode<LruItem>>(concurrencyLevel, this.capacity + 1, comparer);
}
public int Count => this.linkedList.Count;
public double HitRatio => (double)requestHitCount / (double)requestTotalCount;
///<inheritdoc/>
public bool TryGet(K key, out V value)
{
Interlocked.Increment(ref requestTotalCount);
LinkedListNode<LruItem> node;
if (dictionary.TryGetValue(key, out node))
{
LockAndMoveToEnd(node);
Interlocked.Increment(ref requestHitCount);
value = node.Value.Value;
return true;
}
value = default(V);
return false;
}
public V GetOrAdd(K key, Func<K, V> valueFactory)
{
if (this.TryGet(key, out var value))
{
return value;
}
var node = new LinkedListNode<LruItem>(new LruItem(key, valueFactory(key)));
if (this.dictionary.TryAdd(key, node))
{
LinkedListNode<LruItem> first = null;
lock (this.linkedList)
{
if (linkedList.Count >= capacity)
{
first = linkedList.First;
linkedList.RemoveFirst();
}
linkedList.AddLast(node);
}
// Remove from the dictionary outside the lock. This means that the dictionary at this moment
// contains an item that is not in the linked list. If another thread fetches this item,
// LockAndMoveToEnd will ignore it, since it is detached. This means we potentially 'lose' an
// item just as it was about to move to the back of the LRU list and be preserved. The next request
// for the same key will be a miss. Dictionary and list are eventually consistent.
// However, all operations inside the lock are extremely fast, so contention is minimized.
if (first != null)
{
dictionary.TryRemove(first.Value.Key, out var removed);
if (removed.Value.Value is IDisposable d)
{
d.Dispose();
}
}
return node.Value.Value;
}
return this.GetOrAdd(key, valueFactory);
}
public bool TryRemove(K key)
{
if (dictionary.TryRemove(key, out var node))
{
// If the node has already been removed from the list, ignore.
// E.g. thread A reads x from the dictionary. Thread B adds a new item, removes x from
// the List & Dictionary. Now thread A will try to move x to the end of the list.
if (node.List != null)
{
lock (this.linkedList)
{
if (node.List != null)
{
linkedList.Remove(node);
}
}
}
if (node.Value.Value is IDisposable d)
{
d.Dispose();
}
return true;
}
return false;
}
// Thead A reads x from the dictionary. Thread B adds a new item. Thread A moves x to the end. Thread B now removes the new first Node (removal is atomic on both data structures).
private void LockAndMoveToEnd(LinkedListNode<LruItem> node)
{
// If the node has already been removed from the list, ignore.
// E.g. thread A reads x from the dictionary. Thread B adds a new item, removes x from
// the List & Dictionary. Now thread A will try to move x to the end of the list.
if (node.List == null)
{
return;
}
lock (this.linkedList)
{
if (node.List == null)
{
return;
}
linkedList.Remove(node);
linkedList.AddLast(node);
}
}
private class LruItem
{
public LruItem(K k, V v)
{
Key = k;
Value = v;
}
public K Key { get; }
public V Value { get; }
}
}
int capacity = 666;
var lru = new ConcurrentLru<int, SomeItem>(capacity);
var value = lru.GetOrAdd(1, (k) => new SomeItem(k));
Install-Package BitFaster.Caching
您的问题需要更多的澄清。C#是一种语言而不是框架。您必须指定要实现缓存的框架。如果我们考虑您想在ASP.NET中实现它,那么它完全取决于您从缓存中想要什么。您可以在进程内缓存之间进行选择(这将使数据保留在应用程序的堆内),或者在进程外缓存之间进行选择(在这种情况下,您可以将数据存储在除堆之外的其他内存中,例如Amazon Elastic缓存服务器)。还有另一个决策需要做出,即客户端缓存或服务器端缓存之间的选择。通常,在解决方案中,您必须为缓存不同的数据开发不同的解决方案。因为基于四个因素(可访问性、持久性、大小、成本),您必须决定需要哪种解决方案。
我之前写过这个程序,看起来运行得很好。它允许您通过使用不同的类型来区分不同的缓存存储:ApplicationCaching<MyCacheType1>, ApplicationCaching<MyCacheType2>...
。
您可以决定允许某些存储在执行后持久化,而其他存储则会过期。
您需要引用Newtonsoft.Json
序列化器(或使用替代品),当然所有要缓存的对象或值类型都必须可序列化。
使用MaxItemCount
来设置任何一个存储中项目数量的限制。
一个单独的Zipper类(请参见下面的代码)使用System.IO.Compression
。这最小化了存储的大小,并有助于加快加载时间。
public static class ApplicationCaching<K>
{
//====================================================================================================================
public static event EventHandler InitialAccess = (s, e) => { };
//=============================================================================================
static Dictionary<string, byte[]> _StoredValues;
static Dictionary<string, DateTime> _ExpirationTimes = new Dictionary<string, DateTime>();
//=============================================================================================
public static int MaxItemCount { get; set; } = 0;
private static void OnInitialAccess()
{
//-----------------------------------------------------------------------------------------
_StoredValues = new Dictionary<string, byte[]>();
//-----------------------------------------------------------------------------------------
InitialAccess?.Invoke(null, EventArgs.Empty);
//-----------------------------------------------------------------------------------------
}
public static void AddToCache<T>(string key, T value, DateTime expirationTime)
{
try
{
//-----------------------------------------------------------------------------------------
if (_StoredValues is null) OnInitialAccess();
//-----------------------------------------------------------------------------------------
string strValue = JsonConvert.SerializeObject(value);
byte[] zippedValue = Zipper.Zip(strValue);
//-----------------------------------------------------------------------------------------
_StoredValues.Remove(key);
_StoredValues.Add(key, zippedValue);
//-----------------------------------------------------------------------------------------
_ExpirationTimes.Remove(key);
_ExpirationTimes.Add(key, expirationTime);
//-----------------------------------------------------------------------------------------
}
catch (Exception ex)
{
throw ex;
}
}
//=============================================================================================
public static T GetFromCache<T>(string key, T defaultValue = default)
{
try
{
//-----------------------------------------------------------------------------------------
if (_StoredValues is null) OnInitialAccess();
//-----------------------------------------------------------------------------------------
if (_StoredValues.ContainsKey(key))
{
//------------------------------------------------------------------------------------------
if (_ExpirationTimes[key] <= DateTime.Now)
{
//------------------------------------------------------------------------------------------
_StoredValues.Remove(key);
_ExpirationTimes.Remove(key);
//------------------------------------------------------------------------------------------
return defaultValue;
//------------------------------------------------------------------------------------------
}
//------------------------------------------------------------------------------------------
byte[] zippedValue = _StoredValues[key];
//------------------------------------------------------------------------------------------
string strValue = Zipper.Unzip(zippedValue);
T value = JsonConvert.DeserializeObject<T>(strValue);
//------------------------------------------------------------------------------------------
return value;
//------------------------------------------------------------------------------------------
}
else
{
return defaultValue;
}
//---------------------------------------------------------------------------------------------
}
catch (Exception ex)
{
throw ex;
}
}
//=============================================================================================
public static string ConvertCacheToString()
{
//-----------------------------------------------------------------------------------------
if (_StoredValues is null || _ExpirationTimes is null) return "";
//-----------------------------------------------------------------------------------------
List<string> storage = new List<string>();
//-----------------------------------------------------------------------------------------
string strStoredObject = JsonConvert.SerializeObject(_StoredValues);
string strExpirationTimes = JsonConvert.SerializeObject(_ExpirationTimes);
//-----------------------------------------------------------------------------------------
storage.AddRange(new string[] { strStoredObject, strExpirationTimes});
//-----------------------------------------------------------------------------------------
string strStorage = JsonConvert.SerializeObject(storage);
//-----------------------------------------------------------------------------------------
return strStorage;
//-----------------------------------------------------------------------------------------
}
//=============================================================================================
public static void InializeCacheFromString(string strCache)
{
try
{
//-----------------------------------------------------------------------------------------
List<string> storage = JsonConvert.DeserializeObject<List<string>>(strCache);
//-----------------------------------------------------------------------------------------
if (storage != null && storage.Count == 2)
{
//-----------------------------------------------------------------------------------------
_StoredValues = JsonConvert.DeserializeObject<Dictionary<string, byte[]>>(storage.First());
_ExpirationTimes = JsonConvert.DeserializeObject<Dictionary<string, DateTime>>(storage.Last());
//-----------------------------------------------------------------------------------------
if (_ExpirationTimes != null && _StoredValues != null)
{
//-----------------------------------------------------------------------------------------
for (int i = 0; i < _ExpirationTimes.Count; i++)
{
string key = _ExpirationTimes.ElementAt(i).Key;
//-----------------------------------------------------------------------------------------
if (_ExpirationTimes[key] < DateTime.Now)
{
ClearItem(key);
}
//-----------------------------------------------------------------------------------------
}
//-----------------------------------------------------------------------------------------
if (MaxItemCount > 0 && _StoredValues.Count > MaxItemCount)
{
IEnumerable<KeyValuePair<string, DateTime>> countedOutItems = _ExpirationTimes.OrderByDescending(o => o.Value).Skip(MaxItemCount);
for (int i = 0; i < countedOutItems.Count(); i++)
{
ClearItem(countedOutItems.ElementAt(i).Key);
}
}
//-----------------------------------------------------------------------------------------
return;
//-----------------------------------------------------------------------------------------
}
//-----------------------------------------------------------------------------------------
}
//-----------------------------------------------------------------------------------------
_StoredValues = new Dictionary<string, byte[]>();
_ExpirationTimes = new Dictionary<string, DateTime>();
//-----------------------------------------------------------------------------------------
}
catch (Exception)
{
throw;
}
}
//=============================================================================================
public static void ClearItem(string key)
{
//-----------------------------------------------------------------------------------------
if (_StoredValues.ContainsKey(key))
{
_StoredValues.Remove(key);
}
//-----------------------------------------------------------------------------------------
if (_ExpirationTimes.ContainsKey(key))
_ExpirationTimes.Remove(key);
//-----------------------------------------------------------------------------------------
}
//=============================================================================================
}
您可以轻松地使用类似以下代码的缓存功能...
//------------------------------------------------------------------------------------------------------------------------------
string key = "MyUniqueKeyForThisItem";
//------------------------------------------------------------------------------------------------------------------------------
MyType obj = ApplicationCaching<MyCacheType>.GetFromCache<MyType>(key);
//------------------------------------------------------------------------------------------------------------------------------
if (obj == default)
{
obj = new MyType(...);
ApplicationCaching<MyCacheType>.AddToCache(key, obj, DateTime.Now.AddHours(1));
}
string bulkCache = ApplicationCaching<MyType>.ConvertCacheToString();
//--------------------------------------------------------------------------------------------------------
if (bulkCache != "")
{
Properties.Settings.Default.*MyType*DataCachingStore = bulkCache;
}
//--------------------------------------------------------------------------------------------------------
try
{
Properties.Settings.Default.Save();
}
catch (IsolatedStorageException)
{
//handle Isolated Storage exceptions here
}
private static void ApplicationCaching_InitialAccess(object sender, EventArgs e)
{
//-----------------------------------------------------------------------------------------
string storedCache = Properties.Settings.Default.*MyType*DataCachingStore;
ApplicationCaching<MyCacheType>.InializeCacheFromString(storedCache);
//-----------------------------------------------------------------------------------------
}
最后这里是Zipper类...
public class Zipper
{
public static void CopyTo(Stream src, Stream dest)
{
byte[] bytes = new byte[4096];
int cnt;
while ((cnt = src.Read(bytes, 0, bytes.Length)) != 0)
{
dest.Write(bytes, 0, cnt);
}
}
public static byte[] Zip(string str)
{
var bytes = Encoding.UTF8.GetBytes(str);
using (var msi = new MemoryStream(bytes))
using (var mso = new MemoryStream())
{
using (var gs = new GZipStream(mso, CompressionMode.Compress))
{
CopyTo(msi, gs);
}
return mso.ToArray();
}
}
public static string Unzip(byte[] bytes)
{
using (var msi = new MemoryStream(bytes))
using (var mso = new MemoryStream())
{
using (var gs = new GZipStream(msi, CompressionMode.Decompress))
{
CopyTo(gs, mso);
}
return Encoding.UTF8.GetString(mso.ToArray());
}
}
}
Hashtable menuTable = new Hashtable();
menuTable.add("Home","default.aspx");
Cache["menu"] = menuTable;
然后再次检索它
Hashtable menuTable = (Hashtable)Cache["menu"];