aspnetcore中aop的实现

aaspnetcore开发框架中实现aop不仅仅在业务上，在代码的优雅简洁和架构的稳定上都有着至关重要。

下面介绍三种用过的。

第一种通过System.Reflection的DispatchProxy类来实现

首先新建一个aspnetcore项目

针对业务代码WarService加了一个代理的方法

public interface IWarService
    {
        string WipeOut();
        IWarService Proxy(IWarService warService);
    }

 public class WarService : IWarService
    {
        public IWarService Proxy(IWarService warService)
        {
            return WarDispatch<IWarService>.Create(warService);
        }

        public string WipeOut()
        {
            return "us is over";
        }
    }

具体的WarDispatch就是核心代码了，继承自DispatchProxy。这里的before和after的实现就是针对实现了代码的service提前挖坑。

public class WarDispatch<T> : DispatchProxy where T : class
    {
        private T Target { get; set; }
        public static T Create<T>(T target) where T : class
        {
            var proxy = Create<T, WarDispatch<T>>() as WarDispatch<T>;
            proxy.Target = target;
            return proxy as T;
        }

        protected override object? Invoke(MethodInfo? targetMethod, object?[]? args)
        {
            Before().Wait();
            var result = targetMethod.Invoke(Target, args);
            After().Wait();
            return result;
        }

        Task Before()
        {
            return Task.CompletedTask;
        }

        Task After()
        {
            return Task.CompletedTask;
        }
    }

实现代码也相当简单

[ApiController]
    [Route("[controller]")]
    public class RescueEarthController : ControllerBase
    {
        private IWarService _warService;

        public RescueEarthController(IWarService warService)
        {
            _warService = warService;
        }

        [HttpGet(Name = "AnnihilateHegemony")]
        public string AnnihilateHegemony()
        {
            var proxy = _warService.Proxy(_warService); //代理
            return proxy.WipeOut();
        }

        [HttpGet("two")]
        public string AnnihilateHegemonyTwo()
        {
            return _warService.WipeOut();
        }
    }

当然不要忘了注入下服务类

builder.Services.AddScoped<IWarService, WarService>();

上面的方式是我自己想出来的，具体到项目中需要改进的地方应该还有很多，但是足够简单，功能也比较单一。

下面简单介绍下AspectCore.DynamicProxy现成组件的代理使用。

首先引用aspnetcore.extensions.dependencyinjection包

在program中使用动态代码

 builder.Host.UseServiceProviderFactory(new DynamicProxyServiceProviderFactory());
            builder.Services.ConfigureDynamicProxy(o =>{
            //添加aop的配置
            //该项目用attribute所以无需配置

            });

内存的缓存代理

 public class CacheDeleteInterceptorAttribute:AbstractInterceptorAttribute
    {
        private readonly Type[] _types;
        private readonly string[] _methods;
        public CacheDeleteInterceptorAttribute(Type[] types, string[] methods)
        {
            if (types.Length != methods.Length)
            {
                throw new Exception("Types必须跟Methods数量一致");
            }
            _types = types;
            _methods = methods;
        }

        public override async Task Invoke(AspectContext context, AspectDelegate next)
        {
            var cache = context.ServiceProvider.GetService<MemoryCache>();
            await next(context);
            for (int i = 0; i < _types.Length; i++)
            {
                var type = _types[i];
                var method = _methods[i];
                string key = "Methods:" + type.FullName + "." + method;
                cache.Remove(key);
            }
        }
    }

 public class CacheInterceptorAttribute : AbstractInterceptorAttribute
    {
        public override async Task Invoke(AspectContext context, AspectDelegate next)
        {
            bool isAsync = context.IsAsync();
            var methodReturnType = context.GetReturnParameter().Type;
            if(methodReturnType==typeof(void)|| methodReturnType==typeof(Task) || methodReturnType == typeof(ValueTask))
            {
                await next(context);
                return;
            }
            var returnType = methodReturnType;
            if (isAsync)
            {
                returnType = returnType.GenericTypeArguments.FirstOrDefault();
            }
            //string param = GetParaName(context.Parameters); //获取方法的参数名,
            string key = $"Methods:{context.ImplementationMethod.DeclaringType.FullName}.{context.ImplementationMethod.Name}";//获取方法名称，也就是缓存key值
            var cache = context.ServiceProvider.GetService<MemoryCache>(); //可以使用自定义的redis或者其他缓存
            if (cache.Get(key) != null)
            {
                //反射获取缓存值
                var value = typeof(MemoryCache).GetMethod("MemoryCache.Get").MakeGenericMethod(returnType).Invoke(cache, new[] {
                    key
                    //, param
                });
                if (isAsync)
                {

                    //判断是Task还是ValueTask
                    if (methodReturnType == typeof(Task<>).MakeGenericType(returnType))
                    {
                        //反射获取Task<>类型的返回值，相当于Task.FromResult(value)
                        context.ReturnValue = typeof(Task).GetMethod(nameof(Task.FromResult)).MakeGenericMethod(returnType).Invoke(null, new[] { value });
                    }
                    else if (methodReturnType == typeof(ValueTask<>).MakeGenericType(returnType))
                    {
                        //反射构建ValueTask<>类型的返回值，相当于new ValueTask(value)
                        context.ReturnValue = Activator.CreateInstance(typeof(ValueTask<>).MakeGenericType(returnType), value);
                    }
                }
                else
                {
                    context.ReturnValue = value;
                }
                return;
            }
            await next(context);
            object returnValue;
            if (isAsync)
            {
                returnValue = await context.UnwrapAsyncReturnValue();
                //反射获取异步结果的值，相当于(context.ReturnValue as Task<>).Result
                //returnValue = typeof(Task<>).MakeGenericType(returnType).GetProperty(nameof(Task<object>.Result)).GetValue(context.ReturnValue);

            }
            else
            {
                returnValue = context.ReturnValue;
            }
            cache.Set(key
                //, param
                , returnValue);
            if(ExpireSeconds > 0)
            {
                cache.Set(key, TimeSpan.FromSeconds(ExpireSeconds));//设置key的过期时间
            }
        }

        //private string GetParaName(object[] parameters)
        //{
        //    throw new NotImplementedException();
        //}

        /// <summary>
        /// 缓存秒数
        /// </summary>
        public int ExpireSeconds { get; set; }
    }

dbcontext的代理

public class TransactionInterceptorAttribute : AbstractInterceptorAttribute
    {
        //public override async Task Invoke(AspectContext context, AspectDelegate next)
        //{
        //    var dbcontext = context.ServiceProvider.GetService<CommonDbContext>();
        //    if (dbcontext.Database.CurrentTransaction != null)
        //    {
        //        await dbcontext.Database.BeginTransactionAsync();
        //        try
        //        {
        //            await next(context);
        //            await dbcontext.Database.CommitTransactionAsync();
        //        }catch(Exception ex)
        //        {
        //           await dbcontext.Database.RollbackTransactionAsync();
        //            throw ex;
        //        }
        //    }
        //    else
        //    {
        //        await next(context);
        //    }
        //}//一个context

        public override async Task Invoke(AspectContext context, AspectDelegate next)
        {
            var dbcontext = context.ServiceProvider.GetService<CommonDbContext>();
            var dbcontextNext = context.ServiceProvider.GetService<NextDbContext>();
            var transactionManager = dbcontext.Database.GetService<IDbContextTransactionManager>();
            var transaction = await transactionManager.BeginTransactionAsync();

            if (transaction != null)
            {
                await dbcontext.Database.BeginTransactionAsync();
                try
                {
                    await next(context);
                    await transaction.CommitAsync();
                }
                catch (Exception ex)
                {
                    await transaction.RollbackAsync();
                    throw ex;
                }
            }
            else
            {
                await next(context);
            }
        }//多个context
    }

 public class CommonDbContext:DbContext
    {
        public CommonDbContext(DbContextOptions<CommonDbContext> options):base(options)
        {

        }
    }

    public class NextDbContext : DbContext
    {
        public NextDbContext(DbContextOptions<CommonDbContext> options) : base(options)
        {

        }
    }

使用就是这么简单

 public class TestOperatorDbBusiness
    {
        [TransactionInterceptor]
        public async ValueTask Add()
        {
            //TODO事务操作
        }
    }

上面的代理组件功能非常多，项目中需要自己去研究更多更全的用法。

上面代码的demo

exercisebook/AOP at main · liuzhixin405/exercisebook (github.com)

还有Castle.DynamicProxy，这个比较复杂一点。具体用法给个实例demo

exercisebook/AspNetCoreAOP at main · liuzhixin405/exercisebook (github.com)

总结：

一个aspnetcore中需要用到aop的地方非常多，框架自带的中间件，filter过滤器，efcore自带Interceptor都可以拿来用。

中间件例如mediator，这里面的拦截器也非常多，还有好多等待发掘。

当然自己也可以定义一些简单的中间层来做拦截。

相信多了解 在框架中有需要用的地方会事半功倍。