net core天马行空系列：原生DI+AOP实现spring boot注解式编程

       写过spring boot之后，那种无处不在的注解让我非常喜欢，比如属性注入@autowire，配置值注入@value，声明式事物@Transactional等，都非常简洁优雅，那么我就在想，这些在net core里能实现么？经过一番摸索，终于实现并整理成此文。

       IOC方面，个人非常喜欢net core自带的DI，因为他注册服务简洁优雅，3个生命周期通俗易懂，所以就没使用autofac等其他容器，AOP方面，使用了业内鼎鼎大名的Castle.DynamicProxy(简称DP),所以要在nuget中添加Castle.Core的依赖包，这里大家可能会有疑问，利用mvc的actionFilter不就可以实现了么，为什么还要引用DP呢，因为呀，actionFilter只在controller层有效，普通类他就无能为力了，而DP无所不能。

1.定义注解和需要用到的类

属性注入注解

  [AttributeUsage(AttributeTargets.Property)]
    public class AutowiredAttribute : Attribute
    {
    }

配置值注入注解

   [AttributeUsage(AttributeTargets.Property)]
    public class ValueAttribute : Attribute
    {
        public ValueAttribute(string value = "")
        {
            this.Value = value;
        }

        public string Value { get; }
    }

声明式事物注解

   [AttributeUsage(AttributeTargets.Method)]
    public class TransactionalAttribute : Attribute
    {
    }

工作单元接口及实现类，用来实现事物操作，注入级别为scope，一次请求公用一个工作单元实例

    public interface IUnitOfWork : IDisposable
    {
        /// <summary>
        /// 开启事务
        /// </summary>
        void BeginTransaction();
        
        /// <summary>
        /// 提交
        /// </summary>
        void Commit();

        /// <summary>
        /// 事物回滚
        /// </summary>
        void RollBack();
    }

   public class UnitOfWork : IUnitOfWork
    {
        public void BeginTransaction()
        {
            Console.WriteLine("开启事务");
        }

        public void Commit()
        {
            Console.WriteLine("提交事务");
        }

        public void Dispose()
        {
            //throw new System.NotImplementedException();
        }

        public void RollBack()
        {
            Console.WriteLine("回滚事务");
        }
    }

拦截器

  /// <summary>
    /// 事物拦截器
    /// </summary>
    public class TransactionalInterceptor : StandardInterceptor
    {
        private IUnitOfWork Uow { set; get; }

        public TransactionalInterceptor(IUnitOfWork uow)
        {
            Uow = uow;
        }

        protected override void PreProceed(IInvocation invocation)
        {
            Console.WriteLine("{0}拦截前", invocation.Method.Name);

            var method = invocation.TargetType.GetMethod(invocation.Method.Name);
            if (method != null && method.GetCustomAttribute<TransactionalAttribute>() != null)
            {
                Uow.BeginTransaction();
            }
        }

        protected override void PerformProceed(IInvocation invocation)
        {
            invocation.Proceed();
        }

        protected override void PostProceed(IInvocation invocation)
        {
            Console.WriteLine("{0}拦截后， 返回值是{1}", invocation.Method.Name, invocation.ReturnValue);

            var method = invocation.TargetType.GetMethod(invocation.Method.Name);
            if (method != null && method.GetCustomAttribute<TransactionalAttribute>() != null)
            {
                Uow.Commit();
            }
        }
    }

用来测试注入效果的接口以及实现类，这里我们定义一辆汽车，汽车拥有一个引擎（属性注入），它能点火启动，点火操作带事物，这里为了演示【接口-实现类】注入和【实现类】注入2种情况，引擎就没添加接口，只有实现类，并且AOP拦截仅有【实现类】的类时，只能拦截虚方法，所以Start和Stop函数为虚函数。

   /// <summary>
    /// 汽车引擎
    /// </summary>
    public class Engine
    {
        [Value("HelpNumber")]
        public string HelpNumber { set; get; }

        public virtual void Start()
        {
            Console.WriteLine("发动机启动");
            Stop();
        }

        public virtual void Stop()
        {
            Console.WriteLine("发动机熄火,拨打求救电话" + HelpNumber);
        }
    }

   public interface ICar
    {
        Engine Engine { set; get; }

        void Fire();
    }

    public class Car : ICar
    {
        [Autowired]
        public Engine Engine { set; get; }

        [Value("oilNo")]
        public int OilNo { set; get; }

        [Transactional]
        public void Fire()
        {
            Console.WriteLine("加满" + OilNo + "号汽油,点火");
            Engine.Start();
        }
    }

控制器HomeController

 public class HomeController : Controller
    {
        [Autowired]
        public ICar Car{ set; get; }

        [Value("description")]
        public string Description { set; get; }

        public IActionResult Index()
        {
            var car = Car;

            Console.WriteLine(Description);

            Car.Fire();

            return View();
        }
    }

 修改appsettings.json，添加一些测试键值对，（如果测试时发现输出的中文乱码，把appsettings.json保存为utf8格式即可），具体代码如下，

{
  "Logging": {
    "LogLevel": {
      "Default": "Warning"
    }
  },
  "AllowedHosts": "*",
  "oilNo": 95,
  "HelpNumber": "110",
  "description": "我要开始飙车了"
}

2.效果图

从上图可以看到，正常注入，正常开启拦截器和事务，正确读取配置值。

从上图可以看到，我们的控制器，ICar和Engine全部都是动态代理类，注入正常。

3.核心代码

第一部分，添加一个扩展类，名叫SummerBootExtentions.cs，代码如下

public static class SummerBootExtentions
    {
        /// <summary>
        /// 瞬时
        /// </summary>
        /// <typeparam name="TService"></typeparam>
        /// <typeparam name="TImplementation"></typeparam>
        /// <param name="services"></param>
        /// <param name="interceptorTypes"></param>
        /// <returns></returns>
        public static IServiceCollection AddSbTransient<TService, TImplementation>(this IServiceCollection services, params Type[] interceptorTypes)
        {
            return services.AddSbService(typeof(TService), typeof(TImplementation), ServiceLifetime.Transient, interceptorTypes);
        }

        /// <summary>
        /// 请求级别
        /// </summary>
        /// <typeparam name="TService"></typeparam>
        /// <typeparam name="TImplementation"></typeparam>
        /// <param name="services"></param>
        /// <param name="interceptorTypes"></param>
        /// <returns></returns>
        public static IServiceCollection AddSbScoped<TService, TImplementation>(this IServiceCollection services, params Type[] interceptorTypes)
        {
            return services.AddSbService(typeof(TService), typeof(TImplementation), ServiceLifetime.Scoped, interceptorTypes);
        }

        /// <summary>
        /// 单例
        /// </summary>
        /// <typeparam name="TService"></typeparam>
        /// <typeparam name="TImplementation"></typeparam>
        /// <param name="services"></param>
        /// <param name="interceptorTypes"></param>
        /// <returns></returns>
        public static IServiceCollection AddSbSingleton<TService, TImplementation>(this IServiceCollection services, params Type[] interceptorTypes)
        {
            return services.AddSbService(typeof(TService), typeof(TImplementation), ServiceLifetime.Singleton, interceptorTypes);
        }

        public static IServiceCollection AddSbService(this IServiceCollection services, Type serviceType, Type implementationType,
            ServiceLifetime lifetime, params Type[] interceptorTypes)
        {
            services.Add(new ServiceDescriptor(implementationType, implementationType, lifetime));

            object Factory(IServiceProvider provider)
            {
                var target = provider.GetService(implementationType);
                var properties = implementationType.GetTypeInfo().DeclaredProperties;

                foreach (PropertyInfo info in properties)
                {
                    //属性注入
                    if (info.GetCustomAttribute<AutowiredAttribute>() != null)
                    {
                        var propertyType = info.PropertyType;
                        var impl = provider.GetService(propertyType);
                        if (impl != null)
                        {
                            info.SetValue(target, impl);
                        }
                    }

                    //配置值注入
                    if (info.GetCustomAttribute<ValueAttribute>() is ValueAttribute valueAttribute)
                    {
                        var value = valueAttribute.Value;
                        if (provider.GetService(typeof(IConfiguration)) is IConfiguration configService)
                        {
                            var pathValue = configService.GetSection(value).Value;
                            if (pathValue != null)
                            {
                                var pathV = Convert.ChangeType(pathValue, info.PropertyType);
                                info.SetValue(target, pathV);
                            }
                        }

                    }
                }

                List<IInterceptor> interceptors = interceptorTypes.ToList()
                    .ConvertAll<IInterceptor>(interceptorType => provider.GetService(interceptorType) as IInterceptor);

                var proxy = new ProxyGenerator().CreateInterfaceProxyWithTarget(serviceType, target, interceptors.ToArray());

                return proxy;
            };

            var serviceDescriptor = new ServiceDescriptor(serviceType, Factory, lifetime);
            services.Add(serviceDescriptor);

            return services;
        }

        /// <summary>
        /// 瞬时
        /// </summary>
        /// <typeparam name="TService"></typeparam>
        /// <param name="services"></param>
        /// <param name="interceptorTypes"></param>
        /// <returns></returns>
        public static IServiceCollection AddSbTransient<TService>(this IServiceCollection services, params Type[] interceptorTypes)
        {
            return services.AddSbService(typeof(TService), ServiceLifetime.Transient, interceptorTypes);
        }

        /// <summary>
        /// 请求
        /// </summary>
        /// <typeparam name="TService"></typeparam>
        /// <param name="services"></param>
        /// <param name="interceptorTypes"></param>
        /// <returns></returns>
        public static IServiceCollection AddSbScoped<TService>(this IServiceCollection services, params Type[] interceptorTypes)
        {
            return services.AddSbService(typeof(TService), ServiceLifetime.Scoped, interceptorTypes);
        }

        /// <summary>
        /// 单例
        /// </summary>
        /// <typeparam name="TService"></typeparam>
        /// <param name="services"></param>
        /// <param name="interceptorTypes"></param>
        /// <returns></returns>
        public static IServiceCollection AddSbSingleton<TService>(this IServiceCollection services, params Type[] interceptorTypes)
        {
            return services.AddSbService(typeof(TService), ServiceLifetime.Singleton, interceptorTypes);
        }

        public static IServiceCollection AddSbService(this IServiceCollection services, Type serviceType,
            ServiceLifetime lifetime, params Type[] interceptorTypes)
        {
            if (services == null)
                throw new ArgumentNullException(nameof(services));
            if (serviceType == (Type)null)
                throw new ArgumentNullException(nameof(serviceType));

            object Factory(IServiceProvider provider)
            {
                List<IInterceptor> interceptors = interceptorTypes.ToList()
                    .ConvertAll<IInterceptor>(interceptorType => provider.GetService(interceptorType) as IInterceptor);


                var proxy = new ProxyGenerator().CreateClassProxy(serviceType, interceptors.ToArray());

                var properties = serviceType.GetTypeInfo().DeclaredProperties;

                foreach (PropertyInfo info in properties)
                {
                    //属性注入
                    if (info.GetCustomAttribute<AutowiredAttribute>() != null)
                    {
                        var propertyType = info.PropertyType;
                        var impl = provider.GetService(propertyType);
                        if (impl != null)
                        {
                            info.SetValue(proxy, impl);
                        }
                    }

                    //配置值注入
                    if (info.GetCustomAttribute<ValueAttribute>() is ValueAttribute valueAttribute)
                    {
                        var value = valueAttribute.Value;
                        if (provider.GetService(typeof(IConfiguration)) is IConfiguration configService)
                        {
                            var pathValue = configService.GetSection(value).Value;
                            if (pathValue != null)
                            {
                                var pathV = Convert.ChangeType(pathValue, info.PropertyType);
                                info.SetValue(proxy, pathV);
                            }
                        }
                    }
                }

                return proxy;
            };

            var serviceDescriptor = new ServiceDescriptor(serviceType, Factory, lifetime);
            services.Add(serviceDescriptor);

            return services;
        }

        /// <summary>
        /// 添加summer boot扩展
        /// </summary>
        /// <param name="builder"></param>
        /// <returns></returns>
        public static IMvcBuilder AddSB(this IMvcBuilder builder)
        {
            if (builder == null)
                throw new ArgumentNullException(nameof(builder));
            ControllerFeature feature = new ControllerFeature();
            builder.PartManager.PopulateFeature<ControllerFeature>(feature);
            foreach (Type type in feature.Controllers.Select<TypeInfo, Type>((Func<TypeInfo, Type>)(c => c.AsType())))
                builder.Services.TryAddTransient(type, type);
            builder.Services.Replace(ServiceDescriptor.Transient<IControllerActivator, SbControllerActivator>());

            return builder;
        }
    }

第二部分，添加一个自定义控制器激活类，用以替换掉mvc自带的激活类，这个类命名为SbControllerActivator.cs，代码如下

    public class SbControllerActivator : IControllerActivator
    {
        /// <inheritdoc />
        public object Create(ControllerContext actionContext)
        {
            if (actionContext == null)
                throw new ArgumentNullException(nameof(actionContext));

            Type serviceType = actionContext.ActionDescriptor.ControllerTypeInfo.AsType();

            var target = actionContext.HttpContext.RequestServices.GetRequiredService(serviceType);

            var properties = serviceType.GetTypeInfo().DeclaredProperties;
            var proxy = new ProxyGenerator().CreateClassProxyWithTarget(serviceType, target);

            foreach (PropertyInfo info in properties)
            {
                //属性注入
                if (info.GetCustomAttribute<AutowiredAttribute>() != null)
                {
                    var propertyType = info.PropertyType;
                    var impl = actionContext.HttpContext.RequestServices.GetService(propertyType);
                    if (impl != null)
                    {
                        info.SetValue(proxy, impl);
                    }
                }

                //配置值注入
                if (info.GetCustomAttribute<ValueAttribute>() is ValueAttribute valueAttribute)
                {
                    var value = valueAttribute.Value;
                    if (actionContext.HttpContext.RequestServices.GetService(typeof(IConfiguration)) is IConfiguration configService)
                    {
                        var pathValue = configService.GetSection(value).Value;
                        if (pathValue != null)
                        {
                            var pathV = Convert.ChangeType(pathValue, info.PropertyType);
                            info.SetValue(proxy, pathV);
                        }
                    }

                }
            }

            return proxy;
        }

        /// <inheritdoc />
        public virtual void Release(ControllerContext context, object controller)
        {
        }
    }

第三部分，在Startup.cs中，修改ConfigureServices方法如下

 public void ConfigureServices(IServiceCollection services)
        {
            services.Configure<CookiePolicyOptions>(options =>
            {
                // This lambda determines whether user consent for non-essential cookies is needed for a given request.
                options.CheckConsentNeeded = context => true;
                options.MinimumSameSitePolicy = SameSiteMode.None;
            });

            
            services.AddMvc()
                .SetCompatibilityVersion(CompatibilityVersion.Version_2_1)
                .AddSB();

            services.AddSbScoped<Engine>(typeof(TransactionalInterceptor));
            
            services.AddScoped<IUnitOfWork,UnitOfWork>();
            services.AddScoped(typeof(TransactionalInterceptor));

            services.AddSbScoped<ICar, Car>(typeof(TransactionalInterceptor));

        }

       从上面代码我们可以看到，在addMvc后加上了我们替换默认控制器的AddSB方法，接管了控制器的生成。AddSbScoped<Engine>和AddSbScoped<ICar, Car>这种添加依赖注入的方式也保持了net core自带DI的原滋原味，简洁优雅，并且实现了动态代理，只需要在参数里添加拦截器，就能实时拦截，这里参数为params Type[],可以添加N个拦截器。

4.写在最后

   在博客园潜水了好几年，见证了net core从1.0到快出3.0，这也是第一次尝试着写博客，为net core的发扬光大尽自己的一份力。