实现一个基于动态代理的 AOP
Intro
上次看基于动态代理的 AOP 框架实现,立了一个 Flag, 自己写一个简单的 AOP 实现示例,今天过来填坑了
目前的实现是基于 Emit 来做的,后面有时间再写一个基于 Roslyn 来实现的示例
效果演示
演示代码:
切面逻辑定义:
public class TryInvokeAspect : AbstractAspect
{public override void Invoke(MethodInvocationContext methodInvocationContext, Action next){Console.WriteLine($"begin invoke method {methodInvocationContext.ProxyMethod.Name} in {GetType().Name}...");try{next();}catch (Exception e){Console.WriteLine($"Invoke {methodInvocationContext.ProxyMethod.DeclaringType?.FullName}.{methodInvocationContext.ProxyMethod.Name} exception");Console.WriteLine(e);}Console.WriteLine($"end invoke method {methodInvocationContext.ProxyMethod.Name} in {GetType().Name}...");}
}
public class TryInvoke1Aspect : AbstractAspect
{public override void Invoke(MethodInvocationContext methodInvocationContext, Action next){Console.WriteLine($"begin invoke method {methodInvocationContext.ProxyMethod.Name} in {GetType().Name}...");try{next();}catch (Exception e){Console.WriteLine($"Invoke {methodInvocationContext.ProxyMethod.DeclaringType?.FullName}.{methodInvocationContext.ProxyMethod.Name} exception");Console.WriteLine(e);}Console.WriteLine($"end invoke method {methodInvocationContext.ProxyMethod.Name} in {GetType().Name}...");}
}
public class TryInvoke2Aspect : AbstractAspect
{public override void Invoke(MethodInvocationContext methodInvocationContext, Action next){Console.WriteLine($"begin invoke method {methodInvocationContext.ProxyMethod.Name} in {GetType().Name}...");try{next();}catch (Exception e){Console.WriteLine($"Invoke {methodInvocationContext.ProxyMethod.DeclaringType?.FullName}.{methodInvocationContext.ProxyMethod.Name} exception");Console.WriteLine(e);}Console.WriteLine($"end invoke method {methodInvocationContext.ProxyMethod.Name} in {GetType().Name}...");}
}
测试服务定义
// 测试接口定义
public interface ITestService
{[TryInvokeAspect]void Test();[TryInvokeAspect][TryInvoke1Aspect][TryInvoke2Aspect]void Test1(int a, string b);[TryInvokeAspect]string Test2();[TryInvokeAspect]int Test3();
}
// 测试接口实例定义
public class TestService : ITestService
{[TryInvokeAspect]public virtual string TestProp { get; set; }public void Test(){Console.WriteLine("test invoked");}public virtual void Test1(int a, string b){Console.WriteLine($"a:{a}, b:{b}");}[TryInvoke1Aspect]public virtual string Test2(){return "Hello";}[TryInvokeAspect]public virtual int Test3(){return 1;}
}
测试代码:
//var testService = ProxyGenerator.Instance.CreateInterfaceProxy<ITestService>();
var testService = ProxyGenerator.Instance.CreateInterfaceProxy<ITestService, TestService>();
// var testService = ProxyGenerator.Instance.CreateClassProxy<TestService>();
// testService.TestProp = "12133";
testService.Test();
Console.WriteLine();
testService.Test1(1, "str");
var a = testService.Test2();
var b = testService.Test3();
Console.WriteLine($"a:{a}, b:{b}");
Console.ReadLine();
输出效果:
整体结构
ProxyGenerator
ProxyGenerator
代理生成器,用来创建代理对象
public class ProxyGenerator
{public static readonly ProxyGenerator Instance = new ProxyGenerator();public object CreateInterfaceProxy(Type interfaceType){var type = ProxyUtil.CreateInterfaceProxy(interfaceType);return Activator.CreateInstance(type);}public object CreateInterfaceProxy(Type interfaceType, Type implementationType){var type = ProxyUtil.CreateInterfaceProxy(interfaceType, implementationType);return Activator.CreateInstance(type);}public object CreateClassProxy(Type classType, params Type[] interfaceTypes){var type = ProxyUtil.CreateClassProxy(classType, interfaceTypes);return Activator.CreateInstance(type);}public object CreateClassProxy(Type classType, Type implementationType, params Type[] interfaceTypes){var type = ProxyUtil.CreateClassProxy(implementationType, interfaceTypes);return Activator.CreateInstance(type);}
}
为了更方便的使用泛型,定义了几个扩展方法:
public static class Extensions
{public static TInterface CreateInterfaceProxy<TInterface>(this ProxyGenerator proxyGenerator) =>(TInterface)proxyGenerator.CreateInterfaceProxy(typeof(TInterface));public static TInterface CreateInterfaceProxy<TInterface, TImplement>(this ProxyGenerator proxyGenerator) where TImplement : TInterface =>(TInterface)proxyGenerator.CreateInterfaceProxy(typeof(TInterface), typeof(TImplement));public static TClass CreateClassProxy<TClass>(this ProxyGenerator proxyGenerator) where TClass : class =>(TClass)proxyGenerator.CreateClassProxy(typeof(TClass));public static TClass CreateClassProxy<TClass, TImplement>(this ProxyGenerator proxyGenerator) where TImplement : TClass =>(TClass)proxyGenerator.CreateClassProxy(typeof(TClass), typeof(TImplement));
}
AbstractAspect
AbstractAspect
切面抽象类,继承了 Attribute
,可以继承它来实现自己的切面逻辑
public abstract class AbstractAspect : Attribute
{public abstract void Invoke(MethodInvocationContext methodInvocationContext, Action next);
}
MethodInvocationContext
MethodInvocationContext
方法执行上下文,包含了执行方法时的原始方法信息以及代理方法信息,方法参数,方法返回值
public class MethodInvocationContext
{public MethodInfo ProxyMethod { get; }public MethodInfo MethodBase { get; }public object ProxyTarget { get; }public object Target { get; }public object[] Parameters { get; }public object ReturnValue { get; set; }public MethodInvocationContext(MethodInfo method, MethodInfo methodBase, object proxyTarget, object target, object[] parameters){ProxyMethod = method;MethodBase = methodBase;ProxyTarget = proxyTarget;Target = target;Parameters = parameters;}
}
代理方法逻辑
生成代理的方法在上一节已经介绍,主要就是通过 Emit 生成代理类,要写一些 Emit 代码, Emit 不在今天的讨论范围内,这里不多介绍,生成代理方法的时候,会检查方法上的 Attribute
,如果是切面逻辑就注册切面逻辑,最后像 asp.net core 中间件一样组装在一起拼成一个委托。
核心代码如下:
// var invocation = new MethodInvocationContext(method, methodBase, this, parameters);
var localAspectInvocation = il.DeclareLocal(typeof(MethodInvocationContext));
il.Emit(OpCodes.Ldloc, localCurrentMethod);
il.Emit(OpCodes.Ldloc, localMethodBase);
il.Emit(OpCodes.Ldarg_0);
il.Emit(OpCodes.Ldloc, localTarget);
il.Emit(OpCodes.Ldloc, localParameters);
// 创建一个 MethodInvocationContext 实例
il.New(typeof(MethodInvocationContext).GetConstructors()[0]);
il.Emit(OpCodes.Stloc, localAspectInvocation);
// AspectDelegate.InvokeAspectDelegate(invocation);
il.Emit(OpCodes.Ldloc, localAspectInvocation);
var invokeAspectDelegateMethod =typeof(AspectDelegate).GetMethod(nameof(AspectDelegate.InvokeAspectDelegate));
// 执行方法以及注册的切面逻辑
il.Call(invokeAspectDelegateMethod);
il.Emit(OpCodes.Nop);
if (method.ReturnType != typeof(void))
{// 获取方法返回值il.Emit(OpCodes.Ldloc, localAspectInvocation);var getMethod = typeof(MethodInvocationContext).GetProperty("ReturnValue").GetGetMethod();il.EmitCall(OpCodes.Callvirt, getMethod, Type.EmptyTypes);if (method.ReturnType.IsValueType){// 如果是值类型,做一下类型转换il.EmitCastToType(typeof(object), method.ReturnType);}il.Emit(OpCodes.Stloc, localReturnValue);il.Emit(OpCodes.Ldloc, localReturnValue);
}
il.Emit(OpCodes.Ret);
注册并执行切面逻辑代码实现:
// 缓存方法体执行的委托,包含切面逻辑的执行和方法的调用
private static readonly ConcurrentDictionary<string, Action<MethodInvocationContext>> _aspectDelegates = new ConcurrentDictionary<string, Action<MethodInvocationContext>>();
public static void InvokeAspectDelegate(MethodInvocationContext context)
{var action = _aspectDelegates.GetOrAdd($"{context.ProxyMethod.DeclaringType}.{context.ProxyMethod}", m =>{// 获取切面逻辑,这里根据切面类型做了一个去重var aspects = new List<AbstractAspect>(8);if (context.MethodBase != null){// 获取类方法上的切面逻辑foreach (var aspect in context.MethodBase.GetCustomAttributes<AbstractAspect>()){if (!aspects.Exists(x => x.GetType() == aspect.GetType())){aspects.Add(aspect);}}}// 获取接口方法上的切面var methodParameterTypes = context.ProxyMethod.GetParameters().Select(p => p.GetType()).ToArray();foreach (var implementedInterface in context.ProxyTarget.GetType().GetImplementedInterfaces()){var method = implementedInterface.GetMethod(context.ProxyMethod.Name, methodParameterTypes);if (null != method){foreach (var aspect in method.GetCustomAttributes<AbstractAspect>()){if (!aspects.Exists(x => x.GetType() == aspect.GetType())){aspects.Add(aspect);}}}}// 构建切面逻辑执行管道,类似于 asp.net core 里的请求管道, 以原始方法调用作为中间件的最后一步var builder = PipelineBuilder.Create<MethodInvocationContext>(x => x.Invoke());foreach (var aspect in aspects){// 注册切面逻辑builder.Use(aspect.Invoke);}// 构建方法执行委托return builder.Build();});// 执行委托action.Invoke(context);// 检查返回值,防止切面逻辑管道的中断执行导致值类型返回值没有赋值if (context.ProxyMethod.ReturnType != typeof(void)){if (context.ReturnValue == null && context.ProxyMethod.ReturnType.IsValueType){// 为值类型返回值设置默认值作为返回值context.ReturnValue = Activator.CreateInstance(context.ProxyMethod.ReturnType);}}
}
More
以上基本可以实现一个 AOP 功能,但是从扩展性以及功能上来说都还比较欠缺,基于 Attribute
的方式固然可以实现功能,但是太不灵活,如果我要在一个无法修改的接口上的某一个方法做一个切面逻辑,显然只使用 Attribute
是做不到的,还是 Fluent-API 的方式比较灵活。
像做一层 AOP 的抽象,切面逻辑通过 Fluent-API 的方式来注册,大概的 API 可能是这样的:
var settings = FluentAspects.For<ITestService>();
setting.PropertySetter(x=>x.TestProp).InterceptWith<TryInterceptor>().InterceptWith<TryInterceptor1>();
setting.Method(x=> x.Test2()).InterceptWith<TryInterceptor>().InterceptWith<TryInterceptor1>();
然后基于 AspectCore
和 Castle.Core
来实现具体的 AOP 功能,暂时先想一下,争取尽快的发布一个基本可用的版本,然后之前基于 EF Core 的自动审计也可以基于 AOP 来实现了,这样就不需要显示继承 AuditDbContext
了~
文章所有源码可以在 Github 上获取到,Github 地址:https://github.com/WeihanLi/SamplesInPractice/tree/master/AopSample
Reference
让 .NET 轻松构建中间件模式代码
让 .NET 轻松构建中间件模式代码--支持中间件管道的中断和分支
NET 下基于动态代理的 AOP 框架实现揭秘
EF Core 数据变更自动审计设计
AopSample
AspectCore