让MEF插上AOP的翅膀

1. 什么是MEF

   Git：https://github.com/MicrosoftArchive/mef

   MEF也是一款ioc框架，貌似历史比较悠久了。

   这里有一篇.net阵容里面主流ioc比较。

   https://www.cnblogs.com/liping13599168/archive/2011/07/17/2108734.html

    

2. AOP

   引用百度。

   在软件业，AOP为Aspect Oriented Programming的缩写，意为：面向切面编程，通过预编译方式和运行期动态代理实现程序功能的统一维护的一种技术。AOP是OOP的延续，是软件开发中的一个热点，也是Spring框架中的一个重要内容，是函数式编程的一种衍生范型。利用AOP可以对业务逻辑的各个部分进行隔离，从而使得业务逻辑各部分之间的耦合度降低，提高程序的可重用性，同时提高了开发的效率。

3. 背景

   线上有个报表项目，最近监控发现有个报表查询比较频繁，导致db压力大，现需要对查询频次较多的报表进行缓存。

    

4. 代码实现

   Nugget 引用Castle.Core

   1自定义ExportProved

public
class
AOPExportProvider : ExportProvider, IDisposable

{

private
CatalogExportProvider _exportProvider;

 

public AOPExportProvider(Func<ComposablePartCatalog> catalogResolver)

{

_exportProvider = new
CatalogExportProvider(catalogResolver(),true);

 

//support recomposition

_exportProvider.ExportsChanged += (s, e) => OnExportsChanged(e);

_exportProvider.ExportsChanging += (s, e) => OnExportsChanging(e);

}

 

 

public
ExportProvider SourceProvider

{

get

{

return _exportProvider.SourceProvider;

}

set

{

_exportProvider.SourceProvider = value;

}

}

 

 

protected
override
IEnumerable<Export> GetExportsCore(

ImportDefinition definition, AtomicComposition atomicComposition)

{

IEnumerable<Export> exports = _exportProvider.GetExports(definition, atomicComposition);

return exports.Select(export => new
Export(export.Definition, () => GetValue(export)));

}

 

private
object GetValue(Export innerExport)

{

var value = innerExport.Value;

IInterceptor[] attribs = value.GetType().GetCustomAttributes(typeof(IInterceptor), true).Cast<IInterceptor>().ToArray();

if (attribs.Length == 0)

return value;

ProxyGenerator generator = new
ProxyGenerator();

object proxy = generator.CreateClassProxy(value.GetType(), attribs);

 

PropertyInfo[] propertyInfo= value.GetType().GetProperties();

Type proxyType = proxy.GetType().BaseType;

foreach (var item in propertyInfo)

{

PropertyInfo property = proxyType.GetProperty(item.Name);

if (property == null) continue;

property.SetValue(proxy, item.GetValue(value,null),null);

}

return proxy;

}

 

 

public
void Dispose()

{

_exportProvider.Dispose();

}

}

 

2 在web启动的时候 指定自定义exportprovide

public
static
class
MefConfig

{

public
static
void RegisterMef()

{

var container = ConfigureContainer();

ControllerBuilder.Current.SetControllerFactory(new
MefControllerFactory(container));

var dependencyResolver = System.Web.Http.GlobalConfiguration.Configuration.DependencyResolver;

}

 

private
static
CompositionContainer ConfigureContainer()

{

Func<ComposablePartCatalog> catalogResolver = () =>

{

 

AggregateCatalog catalog = new
AggregateCatalog();

catalog.Catalogs.Add(new
DirectoryCatalog(AppDomain.CurrentDomain.SetupInformation.PrivateBinPath, "Mw*.dll"));

return catalog;

};

AOPExportProvider provider = new
AOPExportProvider(catalogResolver);

CompositionContainer container = new
CompositionContainer(provider);

provider.SourceProvider = container;

AppDomain.CurrentDomain.SetData("Container", container);

return container;

}

}

3 实现Interceptor

[Export(typeof(IInterceptor))]

public
class
CacheInterceptor : Attribute, IInterceptor

{

private
ICache _cacheProvider;

public CacheInterceptor(){

_cacheProvider = ((CompositionContainer)AppDomain.CurrentDomain.GetData("Container")).GetExportedValue<ICache>();

}

private
char _linkChar = ':';

public
void Intercept(IInvocation invocation)

{

var qCachingAttribute = this.GetQCachingAttributeInfo(invocation.MethodInvocationTarget ?? invocation.Method);

if (qCachingAttribute != null)

{

ProceedCaching(invocation, qCachingAttribute);

}

else

{

invocation.Proceed();

}

}

private
QCachingAttribute GetQCachingAttributeInfo(MethodInfo method)

{

return method.GetCustomAttributes(true).FirstOrDefault(x => x.GetType() == typeof(QCachingAttribute)) as
QCachingAttribute;

}

private
void ProceedCaching(IInvocation invocation, QCachingAttribute attribute)

{

var cacheKey = attribute.Key;

if(string.IsNullOrEmpty(cacheKey))

cacheKey= GenerateCacheKey(invocation);

 

var cacheValue = _cacheProvider.Get(cacheKey, x => { return
null; });

if (cacheValue != null)

{

invocation.ReturnValue = cacheValue;

return;

}

 

invocation.Proceed();

 

if (!string.IsNullOrWhiteSpace(cacheKey))

{

_cacheProvider.Set(cacheKey, invocation.ReturnValue, TimeSpan.FromSeconds(attribute.AbsoluteExpiration));

}

}

private
string GenerateCacheKey(IInvocation invocation)

{

var typeName = invocation.TargetType.Name;

var methodName = invocation.Method.Name;

var methodArguments = this.FormatArgumentsToPartOfCacheKey(invocation.Arguments);

 

return
this.GenerateCacheKey(typeName, methodName, methodArguments);

}

//拼接缓存的键

private
string GenerateCacheKey(string typeName, string methodName, IList<string> parameters)

{

var builder = new
StringBuilder();

 

builder.Append(typeName);

builder.Append(_linkChar);

 

builder.Append(methodName);

builder.Append(_linkChar);

 

foreach (var param in parameters)

{

builder.Append(param);

builder.Append(_linkChar);

}

 

return builder.ToString().TrimEnd(_linkChar);

}

 

private
IList<string> FormatArgumentsToPartOfCacheKey(IList<object> methodArguments, int maxCount = 5)

{

return methodArguments.Select(this.GetArgumentValue).Take(maxCount).ToList();

}

//处理方法的参数，可根据情况自行调整

private
string GetArgumentValue(object arg)

{

if (arg is
int || arg is
long || arg is
string)

return arg.ToString();

 

if (arg is
DateTime)

return ((DateTime)arg).ToString("yyyyMMddHHmmss");

 

if (arg is
IQCachable)

return ((IQCachable)arg).CacheKey;

 

return
null;

}

}

4 定义拦截Attribute

[AttributeUsage(AttributeTargets.Method, Inherited = true)]

public
class
QCachingAttribute: Attribute

{

public
int AbsoluteExpiration { get; set; } = 30;

public
string Key { get; set; }

}

}

5配置使用Interceptor

[Export(typeof(ICompanyDaily))]

[CacheInterceptor]

public
class
CompanyDaily : ICompanyDaily

{

[Import]

public
ItbshopRepository _shopRepository { get; set; }

[QCaching(AbsoluteExpiration =60*60*8)]

public
virtual
DataTable GetSalesDetailStatistics(DateTime sellDateBegin, DateTime sellDateEnd, string sShopGUID, string mAreaId, int classify, string types)

{

string beginDate = sellDateBegin.ToString("yyyy-MM-dd");

string endDate = sellDateEnd.ToString("yyyy-MM-dd");

try

{

//dosomething

return dtChart;

}

catch (Exception exp)

{

throw exp;

}

}

Ps:拦截的方法必须是virtual