利用.NET Core类库System.Reflection.DispatchProxy实现简易Aop

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背景

Aop即是面向切面编程，众多Aop框架里Castle是最为人所知的，另外还有死去的Spring.NET，当然，.NET Core社区新秀AspectCore在性能与功能上都非常优秀，已经逐渐被社区推崇和有越来越多的人使用。感谢柠檬同学的礼物！

如果大家出于自身需求或者学习，想实现一个Aop，是不是觉得一来就要使用Emit去做？最近我了解到了System.Reflection.DispatchProxy这个corefx类库，已经实现了动态代理功能。

System.Reflection.DispatchProxy

下面演示一下它的使用方法：

class Program { static void Main(string[] args) { //创建代理类，并把SampleProxy作为拦截器注入 var sampleProxy = (targetInterface)SampleProxy.Create<targetInterface, SampleProxy>(); //执行接口方法 sampleProxy.Write("here is invoke by proxy"); } }//需要被生成代理实例的接口 public interface targetInterface { //这个方法会被代理类实现 void Write(string writesomeshing); }public class SampleProxy : DispatchProxy { /// <summary> /// 拦截调用 /// </summary> /// <param name="method">所拦截的方法信息</param> /// <param name="parameters">所拦截方法被传入的参数指</param> /// <returns></returns> protected override object Invoke(MethodInfo targetMethod, object[] args) { Console.WriteLine(args[0]); return null; } }

改造成一款简易AOP

为什么？

System.Reflection.DispatchProxy只有一个Api，就是objecct Create<T,TProxy>() where TProxy:DispatchProxy,约束了只能传入泛型参数，并不能从方法传入类型，这就会带来很多问题。而更可气的是，给官方提了issue之后，还是不给增加这个api……

改造方法

幸好，在那个issue下，issue作者提供了一个解决方案，就是用反射来构造这个泛型方法。我还在这基础上，封装了一下，加入了传入拦截器实例和传入拦截器构造方法参数的功能。

/// <summary> /// 拦截器接口 /// </summary> public interface IInterceptor { /// <summary> /// 拦截器调用 /// </summary> /// <param name="target">代理实例</param> /// <param name="method">所拦截的方法</param> /// <param name="parameters">所拦截方法传入的参数值</param> /// <returns>返回值会传递给方法返回值</returns> object Intercept(object target, MethodInfo method, object[] parameters); }

拦截器要实现这个接口，下面是对DispatchProxy的封装，实现更多创建代理实例的方法

public class ProxyGenerator : DispatchProxy { private IInterceptor interceptor { get; set; } /// <summary> /// 创建代理实例 /// </summary> /// <param name="targetType">所要代理的接口类型</param> /// <param name="interceptor">拦截器</param> /// <returns>代理实例</returns> public static object Create(Type targetType, IInterceptor interceptor) { object proxy = GetProxy(targetType); ((ProxyGenerator)proxy).CreateInstance(interceptor); return proxy; } /// <summary> /// 创建代理实例 /// </summary> /// <param name="targetType">所要代理的接口类型</param> /// <param name="interceptorType">拦截器类型</param> /// <param name="parameters">拦截器构造函数参数值</param> /// <returns>代理实例</returns> public static object Create(Type targetType, Type interceptorType, params object[] parameters) { object proxy = GetProxy(targetType); ((ProxyGenerator)proxy).CreateInstance(interceptorType, parameters); return proxy; } /// <summary> /// 创建代理实例 TTarget:所要代理的接口类型 TInterceptor:拦截器类型 /// </summary> /// <param name="parameters">拦截器构造函数参数值</param> /// <returns>代理实例</returns> public static TTarget Create<TTarget, TInterceptor>(params object[] parameters) where TInterceptor : IInterceptor { var proxy = GetProxy(typeof(TTarget)); ((ProxyGenerator)proxy).CreateInstance(typeof(TInterceptor), parameters); return (TTarget)proxy; } private static object GetProxy(Type targetType) { var callexp = Expression.Call(typeof(DispatchProxy), nameof(DispatchProxy.Create), new[] { targetType, typeof(ProxyGenerator) }); return Expression.Lambda<Func<object>>(callexp).Compile()(); } private void CreateInstance(Type interceptorType, object[] parameters) { var ctorParams = parameters.Select(x => x.GetType()).ToArray(); var paramsExp = parameters.Select(x => Expression.Constant(x)); var newExp = Expression.New(interceptorType.GetConstructor(ctorParams), paramsExp); this.interceptor = Expression.Lambda<Func<IInterceptor>>(newExp).Compile()(); } private void CreateInstance(IInterceptor interceptor) { this.interceptor = interceptor; } protected override object Invoke(MethodInfo method, object[] parameters) { return this.interceptor.Intercept(method, parameters); } }

使用方法

class Program { static void Main(string[] args) { var poxy1 = (targetInterface)ProxyGenerator.Create(typeof(targetInterface), new SampleProxy("coreproxy1")); poxy1.Write("here was invoked"); //---> "here was invoked by coreproxy1" var poxy2 = (targetInterface)ProxyGenerator.Create(typeof(targetInterface), typeof(SampleProxy), "coreproxy2"); poxy2.Write("here was invoked"); //---> "here was invoked by coreproxy2" var poxy3 = ProxyGenerator.Create<targetInterface, SampleProxy>("coreproxy3"); poxy3.Write("here was invoked"); //---> "here was invoked by coreproxy3" } } public class SampleProxy : IInterceptor { private string proxyName { get; } public SampleProxy(string name) { this.proxyName = name; } public object Intercept(MethodInfo method, object[] parameters) { Console.WriteLine(parameters[0] + " by " + proxyName); return null; } } public interface targetInterface { void Write(string writesome); }