关于缓存的设计
1、什么情况下用缓存

缓存是提高应用程序性能的最好方法之一。运用缓存可以优化数据查询，避免不必要的网络数据回传，和避免执行不必要的完全相同的数据处理逻辑。在实现缓存的时候我们要确定什么时候装入缓存数据。用异步装入缓存或用批处理方式来避免出现客户端数据延迟。
一般来说在一定时间内请求了相同的业务逻辑而没有变更的话，可以采用缓存来设计。数据请求频繁的的请求不适合采用缓存，如论坛的回复，但是论坛的主题是可以采用缓存设计的。

2、缓存设计的步骤
确定缓存数据结构：即设计中哪些数据用到了缓存，设计这些数据的缓存结构
确定缓存什么数据
确定缓存过期规则和清理
确定如何装入缓存数据

3、示例 Community Server的缓存类

复制代码 代码如下:
using System;
using System.Collections;
using System.Text.RegularExpressions;
using System.Web;
using System.Web.Caching;

namespace Larry.Cache
{
/// <summary>
/// 缓存类 Community Server的缓存类
/// </summary>
public class BaseCache
{
/// <summary>
/// CacheDependency 说明
/// 如果您向 Cache 中添加某个具有依赖项的项，当依赖项更改时，
/// 该项将自动从 Cache 中删除。例如，假设您向 Cache 中添加某项，
/// 并使其依赖于文件名数组。当该数组中的某个文件更改时，
/// 与该数组关联的项将从缓存中删除。
/// [C#]
/// Insert the cache item.
/// CacheDependency dep = new CacheDependency(fileName, dt);
/// cache.Insert("key", "value", dep);
/// </summary>
public static readonly int DayFactor = ;
public static readonly int HourFactor = ;
public static readonly int MinuteFactor = ;
public static readonly double SecondFactor = 0.;

private static readonly System.Web.Caching.Cache _cache;

private static int Factor = ;

/// <summary>
/// 单件模式
/// </summary>
static BaseCache()
{
HttpContext context = HttpContext.Current;
if (context != null)
{
_cache = context.Cache;
}
else
{
_cache = HttpRuntime.Cache;
}
}

/// <summary>
/// 一次性清除所有缓存
/// </summary>
public static void Clear()
{
IDictionaryEnumerator CacheEnum = _cache.GetEnumerator();
ArrayList al = new ArrayList();
while (CacheEnum.MoveNext()) //逐个清除
{
al.Add(CacheEnum.Key);
}

foreach (string key in al)
{
_cache.Remove(key);
}

}



public static void RemoveByPattern(string pattern)
{
IDictionaryEnumerator CacheEnum = _cache.GetEnumerator();
Regex regex = new Regex(pattern, RegexOptions.IgnoreCase | RegexOptions.Singleline | RegexOptions.Compiled);
while (CacheEnum.MoveNext())
{
if (regex.IsMatch(CacheEnum.Key.ToString()))
_cache.Remove(CacheEnum.Key.ToString());
}
}

/// <summary>
/// 清除特定的缓存
/// </summary>
/// <param name="key"></param>
public static void Remove(string key)
{
_cache.Remove(key);
}

/// <summary>
/// 缓存OBJECT.
/// </summary>
/// <param name="key"></param>
/// <param name="obj"></param>
public static void Insert(string key, object obj)
{
Insert(key, obj, null, );
}

/// <summary>
/// 缓存obj 并建立依赖项
/// </summary>
/// <param name="key"></param>
/// <param name="obj"></param>
/// <param name="dep"></param>
public static void Insert(string key, object obj, CacheDependency dep)
{
Insert(key, obj, dep, MinuteFactor * );
}

/// <summary>
/// 按秒缓存对象
/// </summary>
/// <param name="key"></param>
/// <param name="obj"></param>
/// <param name="seconds"></param>
public static void Insert(string key, object obj, int seconds)
{
Insert(key, obj, null, seconds);
}

/// <summary>
/// 按秒缓存对象 并存储优先级
/// </summary>
/// <param name="key"></param>
/// <param name="obj"></param>
/// <param name="seconds"></param>
/// <param name="priority"></param>
public static void Insert(string key, object obj, int seconds, CacheItemPriority priority)
{
Insert(key, obj, null, seconds, priority);
}

/// <summary>
/// 按秒缓存对象 并建立依赖项
/// </summary>
/// <param name="key"></param>
/// <param name="obj"></param>
/// <param name="dep"></param>
/// <param name="seconds"></param>
public static void Insert(string key, object obj, CacheDependency dep, int seconds)
{
Insert(key, obj, dep, seconds, CacheItemPriority.Normal);
}

/// <summary>
/// 按秒缓存对象 并建立具有优先级的依赖项
/// </summary>
/// <param name="key"></param>
/// <param name="obj"></param>
/// <param name="dep"></param>
/// <param name="seconds"></param>
/// <param name="priority"></param>
public static void Insert(string key, object obj, CacheDependency dep, int seconds, CacheItemPriority priority)
{
if (obj != null)
{
_cache.Insert(key, obj, dep, DateTime.Now.AddSeconds(Factor * seconds), TimeSpan.Zero, priority, null);
}

}

public static void MicroInsert(string key, object obj, int secondFactor)
{
if (obj != null)
{
_cache.Insert(key, obj, null, DateTime.Now.AddSeconds(Factor * secondFactor), TimeSpan.Zero);
}
}

/// <summary>
/// 最大时间缓存
/// </summary>
/// <param name="key"></param>
/// <param name="obj"></param>
public static void Max(string key, object obj)
{
Max(key, obj, null);
}

/// <summary>
/// 具有依赖项的最大时间缓存
/// </summary>
/// <param name="key"></param>
/// <param name="obj"></param>
/// <param name="dep"></param>
public static void Max(string key, object obj, CacheDependency dep)
{
if (obj != null)
{
_cache.Insert(key, obj, dep, DateTime.MaxValue, TimeSpan.Zero, CacheItemPriority.AboveNormal, null);
}
}

/// <summary>
/// Insert an item into the cache for the Maximum allowed time
/// </summary>
/// <param name="key"></param>
/// <param name="obj"></param>
public static void Permanent(string key, object obj)
{
Permanent(key, obj, null);
}

public static void Permanent(string key, object obj, CacheDependency dep)
{
if (obj != null)
{
_cache.Insert(key, obj, dep, DateTime.MaxValue, TimeSpan.Zero, CacheItemPriority.NotRemovable, null);
}
}

public static object Get(string key)
{
return _cache[key];
}

/// <summary>
/// Return int of seconds * SecondFactor
/// </summary>
public static int SecondFactorCalculate(int seconds)
{
// Insert method below takes integer seconds, so we have to round any fractional values
return Convert.ToInt(Math.Round((double)seconds * SecondFactor));
}
}
}

其实这个类就是一个单件模式的设计 和缓存的公共操作方法，其中CacheDependency表示建立缓存依赖项，CacheItemPriority表示缓存的优先级。S使用如下

复制代码 代码如下:
public static CardShop.Model.Systems GetConfig()
{
const string cacheKey = "WebConfig";
CardShop.Model.Systems sampleCacheTable = Larry.Cache.BaseCache.Get(cacheKey) as CardShop.Model.Systems;
if (sampleCacheTable == null)
{
OprationCheck.Message("第一次加载使用缓存");
sampleCacheTable = model;
Larry.Cache.BaseCache.Insert(cacheKey, sampleCacheTable, 24 * Larry.Cache.BaseCache.MinuteFactor);
}
else
{
OprationCheck.Message("已经加载了缓存不需要再加载");
}
return sampleCacheTable;
}