基于DDD的.NET开发框架 - ABP缓存Caching实现

返回ABP系列

ABP是“ASP.NET Boilerplate Project (ASP.NET样板项目)”的简称。

ASP.NET Boilerplate是一个用最佳实践和流行技术开发现代WEB应用程序的新起点，它旨在成为一个通用的WEB应用程序框架和项目模板。

ABP的官方网站：http://www.aspnetboilerplate.com

ABP官方文档：http://www.aspnetboilerplate.com/Pages/Documents

Github上的开源项目：https://github.com/aspnetboilerplate

一、基本概念

ABP中有两种cache的实现方式：MemroyCache 和 RedisCache，两者都继承至ICache接口（准确说是CacheBase抽象类）。ABP核心模块封装了MemroyCache 来实现ABP中的默认缓存功能。 Abp.RedisCache这个模块封装RedisCache来实现缓存（通过StackExchange.Redis这个类库访问redis）。

1、ICacheManager：

缓存的主要接口是ICacheManager。注入该接口并使用该接口获得一个缓存对象：

        public class TestAppService : ApplicationService
        {
            private readonly ICacheManager _cacheManager;

            public TestAppService(ICacheManager cacheManager)
            {
                _cacheManager = cacheManager;
            }

            public Item GetItem(int id)
            {
                //从缓存中获取
                return _cacheManager
                        .GetCache("MyCache")
                        .Get(id.ToString(), () => GetFromDatabase(id)) as Item;
            }

            public Item GetFromDatabase(int id)
            {
                //... 从数据库中检索
            }
        }

不要在构造函数中使用GetCache方法。如果你的类是transient（每次使用都会创建）的，那么这可能会释放缓存，因为第二次创建类的对象时，会再次调用构造函数，之前的第一次的缓存可能会被释放。

2、ICache：

ICacheManager.GetCache方法返回一个ICache。缓存对象是单例的，第一次请求时会创建缓存，以后都是返回相同的缓存对象。因此，我们可以在不同的类（客户端）中共享具有相同名字的相同缓存。

在样例代码中，我们看到了ICache.Get方法的简单使用。它有两个参数：

key：缓存中一个条目的唯一字符串键。

factory：没有找到给定key的缓存条目时调用的action。工厂方法应该创建并返回实际的条目。如果给定的key在缓存中找到了，那么不会调用该action。ICache接口也有像GetOrDefault,Set,Remove,Clear的方法。同时，这些方法也有async版本。

3、ITypedCache：

ICache接口的key为string类型，value为object类型。ITypeCache是ICache的包装器，提供类型安全、泛型的cache。为了将ICache转为ITypedCache，我们可以使用AsTyped扩展方法，如下所示：

ITypedCache<int, Item> myCache = _cacheManager.GetCache("MyCache").AsTyped<int, Item>();

这样，就不需要转换直接可以使用Get方法。

4、配置

缓存的默认有效期是60min。如果你在60min内都没有使用缓存中的元素，那么它会自动从缓存中移除。对于所有的缓存或者特定的某个缓存，你都可以配置有效期。

//为所有缓存配置有效期
Configuration.Caching.ConfigureAll(cache =>
{
    cache.DefaultSlidingExpireTime = TimeSpan.FromHours(2);
});

//为特定的缓存配置有效期
Configuration.Caching.Configure("MyCache", cache =>
{
    cache.DefaultSlidingExpireTime = TimeSpan.FromHours(8);
});

把上面代码放到模块中的PreInitialize方法中。有了这样的配置，MyCache会有8小时的有效期，而其他cache会有2小时有效期。

cache只要首次创建（第一次请求时），就会调用配置的action。配置并不只局限于DefaultSlidingExpireTime（默认有效期），因为cache对象是一个ICache，你可以使用它的属性和方法自由地配置并初始化。

5、Redis缓存集成

ABP默认缓存管理是使用内存缓存。可以使用Redis作为分布式缓存服务器。

首先，需要安装abp.rediscache NuGet包添加到您的应用程序（可以把它安装到您的Web项目）。然后添加一个AbpRedisCacheModule依赖，在你的模块PreInitialize配置使用：

//...引入命名空间
using Abp.Runtime.Caching.Redis;
namespace MyProject.AbpZeroTemplate.Web
{
    [DependsOn(
        //...模块依赖
        typeof(AbpRedisCacheModule))]
    public class MyProjectWebModule : AbpModule
    {
        public override void PreInitialize()
        {
            //...配置
            Configuration.Caching.UseRedis();
        }
        //...other code
    }
}

Abp.RedisCache默认使用“localhost”作为默认连接字符串。您可以将连接字符串添加到配置文件中以重写它:

<add name="Abp.Redis.Cache" connectionString="localhost"/>

还可以添加设置里设置Redis数据库ID。例如:

<add key="Abp.Redis.Cache.DatabaseId" value="2"/>

注：在ABP中使用Redis缓存请先安装Redis服务器，更多redis配置信息

二、ABP缓存Caching源代码分析

目录结构：

类图：

ICache：缓存的接口

using System;
using System.Threading.Tasks;

namespace Abp.Runtime.Caching
{
    /// <summary>
    /// Defines a cache that can be store and get items by keys.
    /// </summary>
    public interface ICache : IDisposable
    {
        /// <summary>
        /// Unique name of the cache.
        /// </summary>
        string Name { get; }

        /// <summary>
        /// Default sliding expire time of cache items.
        /// Default value: 60 minutes. Can be changed by configuration.
        /// </summary>
        TimeSpan DefaultSlidingExpireTime { get; set; }

        /// <summary>
        /// Gets an item from the cache.
        /// </summary>
        /// <param name="key">Key</param>
        /// <param name="factory">Factory method to create cache item if not exists</param>
        /// <returns>Cached item</returns>
        object Get(string key, Func<string, object> factory);

        /// <summary>
        /// Gets an item from the cache.
        /// </summary>
        /// <param name="key">Key</param>
        /// <param name="factory">Factory method to create cache item if not exists</param>
        /// <returns>Cached item</returns>
        Task<object> GetAsync(string key, Func<string, Task<object>> factory);

        /// <summary>
        /// Gets an item from the cache or null if not found.
        /// </summary>
        /// <param name="key">Key</param>
        /// <returns>Cached item or null if not found</returns>
        object GetOrDefault(string key);

        /// <summary>
        /// Gets an item from the cache or null if not found.
        /// </summary>
        /// <param name="key">Key</param>
        /// <returns>Cached item or null if not found</returns>
        Task<object> GetOrDefaultAsync(string key);

        /// <summary>
        /// Saves/Overrides an item in the cache by a key.
        /// </summary>
        /// <param name="key">Key</param>
        /// <param name="value">Value</param>
        /// <param name="slidingExpireTime">Sliding expire time</param>
        void Set(string key, object value, TimeSpan? slidingExpireTime = null);

        /// <summary>
        /// Saves/Overrides an item in the cache by a key.
        /// </summary>
        /// <param name="key">Key</param>
        /// <param name="value">Value</param>
        /// <param name="slidingExpireTime">Sliding expire time</param>
        Task SetAsync(string key, object value, TimeSpan? slidingExpireTime = null);

        /// <summary>
        /// Removes a cache item by it's key.
        /// </summary>
        /// <param name="key">Key</param>
        void Remove(string key);

        /// <summary>
        /// Removes a cache item by it's key (does nothing if given key does not exists in the cache).
        /// </summary>
        /// <param name="key">Key</param>
        Task RemoveAsync(string key);

        /// <summary>
        /// Clears all items in this cache.
        /// </summary>
        void Clear();

        /// <summary>
        /// Clears all items in this cache.
        /// </summary>
        Task ClearAsync();
    }
}

CacheBase：缓存基类

using System;
using System.Threading.Tasks;
using Nito.AsyncEx;

namespace Abp.Runtime.Caching
{
    /// <summary>
    /// Base class for caches.
    /// It's used to simplify implementing <see cref="ICache"/>.
    /// </summary>
    public abstract class CacheBase : ICache
    {
        public string Name { get; private set; }

        public TimeSpan DefaultSlidingExpireTime { get; set; }

        protected readonly object SyncObj = new object();

        private readonly AsyncLock _asyncLock = new AsyncLock();

        /// <summary>
        /// Constructor.
        /// </summary>
        /// <param name="name"></param>
        protected CacheBase(string name)
        {
            Name = name;
            DefaultSlidingExpireTime = TimeSpan.FromHours(1);
        }

        public virtual object Get(string key, Func<string, object> factory)
        {
            var cacheKey = key;
            var item = GetOrDefault(key);
            if (item == null)
            {
                lock (SyncObj)
                {
                    item = GetOrDefault(key);
                    if (item == null)
                    {
                        item = factory(key);
                        if (item == null)
                        {
                            return null;
                        }

                        Set(cacheKey, item);
                    }
                }
            }

            return item;
        }

        public virtual async Task<object> GetAsync(string key, Func<string, Task<object>> factory)
        {
            var cacheKey = key;
            var item = await GetOrDefaultAsync(key);
            if (item == null)
            {
                using (await _asyncLock.LockAsync())
                {
                    item = await GetOrDefaultAsync(key);
                    if (item == null)
                    {
                        item = await factory(key);
                        if (item == null)
                        {
                            return null;
                        }

                        await SetAsync(cacheKey, item);
                    }
                }
            }

            return item;
        }

        public abstract object GetOrDefault(string key);

        public virtual Task<object> GetOrDefaultAsync(string key)
        {
            return Task.FromResult(GetOrDefault(key));
        }

        public abstract void Set(string key, object value, TimeSpan? slidingExpireTime = null);

        public virtual Task SetAsync(string key, object value, TimeSpan? slidingExpireTime = null)
        {
            Set(key, value, slidingExpireTime);
            return Task.FromResult(0);
        }

        public abstract void Remove(string key);

        public virtual Task RemoveAsync(string key)
        {
            Remove(key);
            return Task.FromResult(0);
        }

        public abstract void Clear();

        public virtual Task ClearAsync()
        {
            Clear();
            return Task.FromResult(0);
        }

        public virtual void Dispose()
        {

        }
    }
}

ITypedCache/TypedCacheWrapper: 支持泛型key和value的缓存接口与实现，其内部通过封装ICache实例和CacheExtension定义的对ICache的扩展方法来是实现泛型版本的Icache.

using System;
using System.Threading.Tasks;

namespace Abp.Runtime.Caching
{
    /// <summary>
    /// Implements <see cref="ITypedCache{TKey,TValue}"/> to wrap a <see cref="ICache"/>.
    /// </summary>
    /// <typeparam name="TKey"></typeparam>
    /// <typeparam name="TValue"></typeparam>
    public class TypedCacheWrapper<TKey, TValue> : ITypedCache<TKey, TValue>
    {
        public string Name
        {
            get { return InternalCache.Name; }
        }

        public TimeSpan DefaultSlidingExpireTime
        {
            get { return InternalCache.DefaultSlidingExpireTime; }
            set { InternalCache.DefaultSlidingExpireTime = value; }
        }

        public ICache InternalCache { get; private set; }

        /// <summary>
        /// Creates a new <see cref="TypedCacheWrapper{TKey,TValue}"/> object.
        /// </summary>
        /// <param name="internalCache">The actual internal cache</param>
        public TypedCacheWrapper(ICache internalCache)
        {
            InternalCache = internalCache;
        }

        public void Dispose()
        {
            InternalCache.Dispose();
        }

        public void Clear()
        {
            InternalCache.Clear();
        }

        public Task ClearAsync()
        {
            return InternalCache.ClearAsync();
        }

        public TValue Get(TKey key, Func<TKey, TValue> factory)
        {
            return InternalCache.Get(key, factory);
        }

        public Task<TValue> GetAsync(TKey key, Func<TKey, Task<TValue>> factory)
        {
            return InternalCache.GetAsync(key, factory);
        }

        public TValue GetOrDefault(TKey key)
        {
            return InternalCache.GetOrDefault<TKey, TValue>(key);
        }

        public Task<TValue> GetOrDefaultAsync(TKey key)
        {
            return InternalCache.GetOrDefaultAsync<TKey, TValue>(key);
        }

        public void Set(TKey key, TValue value, TimeSpan? slidingExpireTime = null)
        {
            InternalCache.Set(key.ToString(), value, slidingExpireTime);
        }

        public Task SetAsync(TKey key, TValue value, TimeSpan? slidingExpireTime = null)
        {
            return InternalCache.SetAsync(key.ToString(), value, slidingExpireTime);
        }

        public void Remove(TKey key)
        {
            InternalCache.Remove(key.ToString());
        }

        public Task RemoveAsync(TKey key)
        {
            return InternalCache.RemoveAsync(key.ToString());
        }
    }
}

CacheExtension: 定义了ICache的扩展方法. 最关键的是如下两个支持泛型的方法：GetOrDefault和GetOrDefaultAsync。如下，内部调用ICache实例的相应方法并通过类型转换。

using System;
using System.Threading.Tasks;

namespace Abp.Runtime.Caching
{
    /// <summary>
    /// Extension methods for <see cref="ICache"/>.
    /// </summary>
    public static class CacheExtensions
    {
        public static object Get(this ICache cache, string key, Func<object> factory)
        {
            return cache.Get(key, k => factory());
        }

        public static Task<object> GetAsync(this ICache cache, string key, Func<Task<object>> factory)
        {
            return cache.GetAsync(key, k => factory());
        }

        public static ITypedCache<TKey, TValue> AsTyped<TKey, TValue>(this ICache cache)
        {
            return new TypedCacheWrapper<TKey, TValue>(cache);
        }
        
        public static TValue Get<TKey, TValue>(this ICache cache, TKey key, Func<TKey, TValue> factory)
        {
            return (TValue)cache.Get(key.ToString(), (k) => (object)factory(key));
        }

        public static TValue Get<TKey, TValue>(this ICache cache, TKey key, Func<TValue> factory)
        {
            return cache.Get(key, (k) => factory());
        }

        public static async Task<TValue> GetAsync<TKey, TValue>(this ICache cache, TKey key, Func<TKey, Task<TValue>> factory)
        {
            var value = await cache.GetAsync(key.ToString(), async (keyAsString) =>
            {
                var v = await factory(key);
                return (object)v;
            });

            return (TValue)value;
        }

        public static Task<TValue> GetAsync<TKey, TValue>(this ICache cache, TKey key, Func<Task<TValue>> factory)
        {
            return cache.GetAsync(key, (k) => factory());
        }

        public static TValue GetOrDefault<TKey, TValue>(this ICache cache, TKey key)
        {
            var value = cache.GetOrDefault(key.ToString());
            if (value == null)
            {
                return default(TValue);
            }

            return (TValue) value;
        }

        public static async Task<TValue> GetOrDefaultAsync<TKey, TValue>(this ICache cache, TKey key)
        {
            var value = await cache.GetOrDefaultAsync(key.ToString());
            if (value == null)
            {
                return default(TValue);
            }

            return (TValue)value;
        }
    }
}

AbpCacheNames:定义了四个cache的key常量,这几个cache是供ABP框架使用的

namespace Abp.Runtime.Caching
{
    /// <summary>
    /// Names of standard caches used in ABP.
    /// </summary>
    public static class AbpCacheNames
    {
        /// <summary>
        /// Application settings cache: AbpApplicationSettingsCache.
        /// </summary>
        public const string ApplicationSettings = "AbpApplicationSettingsCache";

        /// <summary>
        /// Tenant settings cache: AbpTenantSettingsCache.
        /// </summary>
        public const string TenantSettings = "AbpTenantSettingsCache";

        /// <summary>
        /// User settings cache: AbpUserSettingsCache.
        /// </summary>
        public const string UserSettings = "AbpUserSettingsCache";

        /// <summary>
        /// Localization scripts cache: AbpLocalizationScripts.
        /// </summary>
        public const string LocalizationScripts = "AbpLocalizationScripts";
    }
}

ICacheConfigurator/CacheConfigurator：封装了cache的name和对该cahce的初始化方法，通过初始化方法可以完成对cache的配置

using System;

namespace Abp.Runtime.Caching.Configuration
{
    internal class CacheConfigurator : ICacheConfigurator
    {
        public string CacheName { get; private set; }

        public Action<ICache> InitAction { get; private set; }

        public CacheConfigurator(Action<ICache> initAction)
        {
            InitAction = initAction;
        }

        public CacheConfigurator(string cacheName, Action<ICache> initAction)
        {
            CacheName = cacheName;
            InitAction = initAction;
        }
    }
}

ICachingConfiguration/CachingConfiguration: 该接口提供完成cache的配置的方法。具体是通过封装了一个ICacheConfigurator集合，并调用CacheConfigurator的InitAction来配置cache。

using System;
using System.Collections.Generic;
using System.Collections.Immutable;
using Abp.Configuration.Startup;

namespace Abp.Runtime.Caching.Configuration
{
    internal class CachingConfiguration : ICachingConfiguration
    {
        public IAbpStartupConfiguration AbpConfiguration { get; private set; }

        public IReadOnlyList<ICacheConfigurator> Configurators
        {
            get { return _configurators.ToImmutableList(); }
        }
        private readonly List<ICacheConfigurator> _configurators;

        public CachingConfiguration(IAbpStartupConfiguration abpConfiguration)
        {
            AbpConfiguration = abpConfiguration;

            _configurators = new List<ICacheConfigurator>();
        }

        public void ConfigureAll(Action<ICache> initAction)
        {
            _configurators.Add(new CacheConfigurator(initAction));
        }

        public void Configure(string cacheName, Action<ICache> initAction)
        {
            _configurators.Add(new CacheConfigurator(cacheName, initAction));
        }
    }
}

ICacheManager/CacheManagerBase: 该接口和实现用于生成，配置以及销毁ICache实例。具体是通过ICachingConfiguration对象来初始化cache, 并通过ConcurrentDictionary<string, ICache>来存放和管理cache.

AbpMemoryCache：通过MemoryCache来实现Icache.

AbpMemoryCacheManager：重写了CacheManagerBase的CreateCacheImplementation方法，该方法用于创建真实的Icache对象。 具体到AbpMemoryCacheManager就是创建AbpMemoryCache。