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  • ASP.NET Core中IOC容器的实现原理

本章将和大家分享ASP.NET Core中IOC容器的实现原理。

首先我们需要了解什么是IOC,为什么要使用IOC容器?

一、依赖

类A用到了类B,我们就说类A依赖类B。

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using System;

namespace MyIOCDI
{
    public class Test
    {
        public void Show()
        {
            MyDependency myDependency = new MyDependency(); //全是细节
            myDependency.Show();
            Console.WriteLine($"This is {this.GetType().FullName}");
        }
    }

    public class MyDependency
    {
        public void Show()
        {
            Console.WriteLine($"This is {this.GetType().FullName}");
        }
    }
}
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上面的示例中,类Test就依赖了MyDependency类。

二、依赖倒置原则(Dependence Inversion Principle)

依赖倒置原则:高层模块不应该依赖于低层模块,二者都应该依赖于抽象。应该依赖于抽象,而不是依赖细节。

什么是高层模块?这里的使用者Test类就称为高层模块。什么是低层模块?被使用者MyDependency类就称为低层模块。上面的示例中我们的高层模块就依赖于我们的低层模块。

那么这样子有什么不好呢?

  1、面向对象语言开发,就是类与类之间进行交互,如果高层直接依赖低层的细节,细节是多变的,那么低层的变化就导致上层的变化;

  2、如果层数多了,低层的修改会直接水波效应传递到最上层,一点细微的改动都会导致整个系统从下往上的修改。

因此,上例按照依赖倒置原则修改如下:

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using System;

namespace MyIOCDI
{
    public class Test
    {
        public void Show()
        {
            IDepenency myDependency = new MyDependency(); //左边抽象右边细节
            myDependency.Show();
            Console.WriteLine($"This is {this.GetType().FullName}");
        }
    }

    public class MyDependency : IDepenency
    {
        public void Show()
        {
            Console.WriteLine($"This is {this.GetType().FullName}");
        }
    }

    public interface IDepenency
    {
        void Show();
    }
}
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三、IOC控制反转

控制反转是一种思想,所谓“控制反转”就是反转获得依赖对象的过程。

上面示例经过改造后虽然遵循了“依赖倒置原则”,但是违背了“开放封闭原则”,因为如果有一天想要修改变量myDependency为YourDependency类的实例,则需要修改Test类。

因此,我们需要反转这种创建对象的过程:

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using System;

namespace MyIOCDI
{
    public class Test
    {
        private readonly IDepenency _myDependency;
        public Test(IDepenency myDependency)
        {
            this._myDependency = myDependency;
        }

        public void Show()
        {
            _myDependency.Show();
            Console.WriteLine($"This is {this.GetType().FullName}");
        }
    }

    public class MyDependency : IDepenency
    {
        public void Show()
        {
            Console.WriteLine($"This is {this.GetType().FullName}");
        }
    }

    public interface IDepenency
    {
        void Show();
    }
}
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上例中,将 _myDependency 的创建过程“反转”给了调用者。

四、依赖注入(Dependency Injection)

依赖注入是一种在类及其依赖对象之间实现控制反转(IOC)思想的技术。

所谓依赖注入,就是由IOC容器在运行期间,动态地将某种依赖关系注入到对象之中。

依赖注入就是能做到构造某个对象时,将依赖的对象自动初始化并注入 。

IOC是目标是效果,需要DI依赖注入的手段。

三种注入方式:构造函数注入--属性注入--方法注入(按时间顺序)。

构造函数注入用的最多,默认找参数最多的构造函数,可以不用特性,可以去掉对容器的依赖。

五、IOC容器的实现原理

IOC容器的实现原理:

  1、启动时保存注册信息。

  2、在构造某个对象时,根据注册信息使用反射加特性,将依赖的对象自动初始化并注入。

  3、对对象进行生命周期管理或者进行AOP扩展等。

下面我们重点来看下如何创建一个简易的IOC容器(当然,实际使用的IOC容器要比这复杂的多)。

首先来看下项目的目录结构:

此处IOC容器中用到的自定义特性如下所示:

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using System;

namespace TianYaSharpCore.IOCDI.CustomAttribute
{
    /// <summary>
    /// 构造函数注入特性
    /// </summary>
    [AttributeUsage(AttributeTargets.Constructor)]
    public class ConstructorInjectionAttribute : Attribute
    {

    }
}
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using System;

namespace TianYaSharpCore.IOCDI.CustomAttribute
{
    /// <summary>
    /// 方法注入特性
    /// </summary>
    [AttributeUsage(AttributeTargets.Method)]
    public class MethodInjectionAttribute : Attribute
    {

    }
}
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using System;

namespace TianYaSharpCore.IOCDI.CustomAttribute
{
    /// <summary>
    /// 常量
    /// </summary>
    [AttributeUsage(AttributeTargets.Parameter)]
    public class ParameterConstantAttribute : Attribute
    {

    }
}
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using System;

namespace TianYaSharpCore.IOCDI.CustomAttribute
{
    /// <summary>
    /// 简称(别名)
    /// </summary>
    [AttributeUsage(AttributeTargets.Parameter | AttributeTargets.Property)]
    public class ParameterShortNameAttribute : Attribute
    {
        public string ShortName { get; private set; }
        public ParameterShortNameAttribute(string shortName)
        {
            this.ShortName = shortName;
        }
    }
}
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using System;

namespace TianYaSharpCore.IOCDI.CustomAttribute
{
    /// <summary>
    /// 属性注入特性
    /// </summary>
    [AttributeUsage(AttributeTargets.Property)]
    public class PropertyInjectionAttribute : Attribute
    {

    }
}
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创建一个简易的IOC容器,如下所示:

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using System;

namespace TianYaSharpCore.IOCDI.CustomContainer
{
    public class IOCContainerRegistModel
    {
        public Type TargetType { get; set; }

        /// <summary>
        /// 生命周期
        /// </summary>
        public LifetimeType Lifetime { get; set; }

        /// <summary>
        /// 仅限单例
        /// </summary>
        public object SingletonInstance { get; set; }
    }

    /// <summary>
    /// 生命周期
    /// </summary>
    public enum LifetimeType
    {
        Transient, //瞬时
        Singleton,
        Scope, //作用域
        PerThread //线程单例
        //外部可释放单例
    }
}
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using System;

namespace TianYaSharpCore.IOCDI.CustomContainer
{
    /// <summary>
    /// IOC容器接口
    /// </summary>
    public interface ITianYaIOCContainer
    {
        void Register<TFrom, TTo>(string shortName = null, object[] paraList = null, LifetimeType lifetimeType = LifetimeType.Transient)
            where TTo : TFrom;
        TFrom Resolve<TFrom>(string shortName = null);
        ITianYaIOCContainer CreateChildContainer();
    }
}
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using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;

using TianYaSharpCore.IOCDI.CustomAttribute;

namespace TianYaSharpCore.IOCDI.CustomContainer
{
    /// <summary>
    /// IOC容器
    /// </summary>
    public class TianYaIOCContainer : ITianYaIOCContainer
    {
        #region 字段或者属性

        /// <summary>
        /// 保存注册信息
        /// </summary>
        private Dictionary<string, IOCContainerRegistModel> _tianYaContainerDictionary = new Dictionary<string, IOCContainerRegistModel>();

        /// <summary>
        /// 保存常量的值
        /// </summary>
        private Dictionary<string, object[]> _tianYaContainerValueDictionary = new Dictionary<string, object[]>();

        /// <summary>
        /// 作用域单例的对象
        /// </summary>
        private Dictionary<string, object> _tianYaContainerScopeDictionary = new Dictionary<string, object>();

        #endregion 字段或者属性

        #region 构造函数

        /// <summary>
        /// 无参构造行数
        /// </summary>
        public TianYaIOCContainer()
        {

        }

        /// <summary>
        /// 主要在创建子容器的时候使用
        /// </summary>
        private TianYaIOCContainer(Dictionary<string, IOCContainerRegistModel> tianYaContainerDictionary,
            Dictionary<string, object[]> tianYaContainerValueDictionary, Dictionary<string, object> tianYaContainerScopeDictionary)
        {
            this._tianYaContainerDictionary = tianYaContainerDictionary;
            this._tianYaContainerValueDictionary = tianYaContainerValueDictionary;
            this._tianYaContainerScopeDictionary = tianYaContainerScopeDictionary;
        }

        #endregion 构造函数

        /// <summary>
        /// 创建子容器
        /// </summary>
        public ITianYaIOCContainer CreateChildContainer()
        {
            return new TianYaIOCContainer(this._tianYaContainerDictionary, this._tianYaContainerValueDictionary,
                new Dictionary<string, object>()); //没有注册关系,最好能初始化进去
        }

        /// <summary>
        /// 获取键
        /// </summary>
        private string GetKey(string fullName, string shortName) => $"{fullName}___{shortName}";

        /// <summary>
        /// 加个参数区分生命周期--而且注册关系得保存生命周期
        /// </summary>
        /// <typeparam name="TFrom">要添加的服务的类型</typeparam>
        /// <typeparam name="TTo">要使用的实现的类型</typeparam>
        /// <param name="shortName">简称(别名)(主要用于解决单接口多实现)</param>
        /// <param name="paraList">常量参数</param>
        /// <param name="lifetimeType">生命周期</param>
        public void Register<TFrom, TTo>(string shortName = null, object[] paraList = null, LifetimeType lifetimeType = LifetimeType.Transient)
            where TTo : TFrom
        {
            this._tianYaContainerDictionary.Add(this.GetKey(typeof(TFrom).FullName, shortName), new IOCContainerRegistModel()
            {
                Lifetime = lifetimeType,
                TargetType = typeof(TTo)
            });

            if (paraList != null && paraList.Length > 0)
            {
                this._tianYaContainerValueDictionary.Add(this.GetKey(typeof(TFrom).FullName, shortName), paraList);
            }
        }

        /// <summary>
        /// 获取对象
        /// </summary>
        public TFrom Resolve<TFrom>(string shortName = null)
        {
            return (TFrom)this.ResolveObject(typeof(TFrom), shortName);
        }

        /// <summary>
        /// 递归--可以完成不限层级的对象创建
        /// </summary>
        private object ResolveObject(Type abstractType, string shortName = null)
        {
            string key = this.GetKey(abstractType.FullName, shortName);
            var model = this._tianYaContainerDictionary[key];

            #region 生命周期

            switch (model.Lifetime)
            {
                case LifetimeType.Transient:
                    Console.WriteLine("Transient Do Nothing Before");
                    break;
                case LifetimeType.Singleton:
                    if (model.SingletonInstance == null)
                    {
                        break;
                    }
                    else
                    {
                        return model.SingletonInstance;
                    }
                case LifetimeType.Scope:
                    if (this._tianYaContainerScopeDictionary.ContainsKey(key))
                    {
                        return this._tianYaContainerScopeDictionary[key];
                    }
                    else
                    {
                        break;
                    }
                default:
                    break;
            }

            #endregion 生命周期

            Type type = model.TargetType;

            #region 选择合适的构造函数

            ConstructorInfo ctor = null;
            //标记特性
            ctor = type.GetConstructors().FirstOrDefault(c => c.IsDefined(typeof(ConstructorInjectionAttribute), true));
            if (ctor == null)
            {
                //参数个数最多
                ctor = type.GetConstructors().OrderByDescending(c => c.GetParameters().Length).First();
            }
            //ctor = type.GetConstructors()[0]; //直接第一个

            #endregion 选择合适的构造函数

            #region 准备构造函数的参数

            List<object> paraList = new List<object>();
            object[] paraConstant = this._tianYaContainerValueDictionary.ContainsKey(key) ? this._tianYaContainerValueDictionary[key] : null; //常量找出来
            int iIndex = 0;
            foreach (var para in ctor.GetParameters())
            {
                if (para.IsDefined(typeof(ParameterConstantAttribute), true))
                {
                    paraList.Add(paraConstant[iIndex]);
                    iIndex++;
                }
                else
                {
                    Type paraType = para.ParameterType; //获取参数的类型
                    string paraShortName = this.GetShortName(para);
                    object paraInstance = this.ResolveObject(paraType, paraShortName);
                    paraList.Add(paraInstance);
                }
            }

            #endregion 准备构造函数的参数

            object oInstance = null;
            oInstance = Activator.CreateInstance(type, paraList.ToArray()); //创建对象,完成构造函数的注入

            #region 属性注入

            foreach (var prop in type.GetProperties().Where(p => p.IsDefined(typeof(PropertyInjectionAttribute), true)))
            {
                Type propType = prop.PropertyType;
                string paraShortName = this.GetShortName(prop);
                object propInstance = this.ResolveObject(propType, paraShortName);
                prop.SetValue(oInstance, propInstance);
            }

            #endregion 属性注入

            #region 方法注入 

            foreach (var method in type.GetMethods().Where(m => m.IsDefined(typeof(MethodInjectionAttribute), true)))
            {
                List<object> paraInjectionList = new List<object>();
                foreach (var para in method.GetParameters())
                {
                    Type paraType = para.ParameterType;//获取参数的类型 IUserDAL
                    string paraShortName = this.GetShortName(para);
                    object paraInstance = this.ResolveObject(paraType, paraShortName);
                    paraInjectionList.Add(paraInstance);
                }
                method.Invoke(oInstance, paraInjectionList.ToArray());
            }

            #endregion 方法注入

            #region 生命周期

            switch (model.Lifetime)
            {
                case LifetimeType.Transient:
                    Console.WriteLine("Transient Do Nothing After");
                    break;
                case LifetimeType.Singleton:
                    model.SingletonInstance = oInstance;
                    break;
                case LifetimeType.Scope:
                    this._tianYaContainerScopeDictionary[key] = oInstance;
                    break;
                default:
                    break;
            }

            #endregion 生命周期

            //return oInstance.AOP(abstractType); //AOP扩展
            return oInstance;
        }

        /// <summary>
        /// 获取简称(别名)
        /// </summary>
        private string GetShortName(ICustomAttributeProvider provider)
        {
            if (provider.IsDefined(typeof(ParameterShortNameAttribute), true))
            {
                var attribute = (ParameterShortNameAttribute)(provider.GetCustomAttributes(typeof(ParameterShortNameAttribute), true)[0]);
                return attribute.ShortName;
            }
            else
            {
                return null;
            }
        }
    }
}
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至此,我们就创建完了一个简易的IOC容器。

下面我们来添加一些用于测试的接口,如下所示:

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using System;

namespace MyIOCDI.IService
{
    public interface ITestServiceA
    {
        void Show();
    }
}
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using System;

namespace MyIOCDI.IService
{
    public interface ITestServiceB
    {
        void Show();
    }
}
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using System;

namespace MyIOCDI.IService
{
    public interface ITestServiceC
    {
        void Show();
    }
}
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using System;

namespace MyIOCDI.IService
{
    public interface ITestServiceD
    {
        void Show();
    }
}
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接口对应的实现,如下所示:

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using System;

using MyIOCDI.IService;

namespace MyIOCDI.Service
{
    public class TestServiceA : ITestServiceA
    {
        public TestServiceA()
        {
            Console.WriteLine($"{this.GetType().Name}被构造。。。");
        }

        public void Show()
        {
            Console.WriteLine($"This is {this.GetType().Name} Show");
        }
    }
}
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using System;

using MyIOCDI.IService;

namespace MyIOCDI.Service
{
    public class TestServiceB : ITestServiceB
    {
        public TestServiceB()
        {
            Console.WriteLine($"{this.GetType().Name}被构造。。。");
        }

        public void Show()
        {
            Console.WriteLine($"This is {this.GetType().Name} Show");
        }
    }
}
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using System;

using MyIOCDI.IService;

namespace MyIOCDI.Service
{
    public class TestServiceC : ITestServiceC
    {
        public TestServiceC()
        {
            Console.WriteLine($"{this.GetType().Name}被构造。。。");
        }

        public void Show()
        {
            Console.WriteLine($"This is {this.GetType().Name} Show");
        }
    }
}
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using System;

using MyIOCDI.IService;
using TianYaSharpCore.IOCDI.CustomAttribute;

namespace MyIOCDI.Service
{
    public class TestServiceD : ITestServiceD
    {
        /// <summary>
        /// 属性注入
        /// </summary>
        [PropertyInjection]
        public ITestServiceA TestServiceA { get; set; }

        /// <summary>
        /// 带有别名的属性注入
        /// </summary>
        [ParameterShortName("ServiceB")]
        [PropertyInjection]
        public ITestServiceB TestServiceB { get; set; }

        public TestServiceD()
        {
            Console.WriteLine($"{this.GetType().Name}被构造。。。");
        }

        #region 构造函数注入

        private readonly ITestServiceA _testServiceA;
        private readonly ITestServiceB _testServiceB;
        [ConstructorInjection] //优先选择带有构造函数注入特性的
        public TestServiceD(ITestServiceA testServiceA, [ParameterConstant] string sValue, ITestServiceB testServiceB, [ParameterConstant] int iValue)
        {
            Console.WriteLine($"{this.GetType().Name}--{sValue}--{iValue}被构造。。。");
            _testServiceA = testServiceA;
            _testServiceB = testServiceB;
        }

        #endregion 构造函数注入

        #region 方法注入

        private ITestServiceC _testServiceC;
        [MethodInjection]
        public void Init(ITestServiceC testServiceC)
        {
            _testServiceC = testServiceC;
        }

        #endregion 方法注入

        public void Show()
        {
            Console.WriteLine($"This is {this.GetType().Name} Show");
        }
    }
}
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最后来看下IOC容器的使用及其运行结果:

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using System;

using TianYaSharpCore.IOCDI.CustomContainer;
using MyIOCDI.IService;
using MyIOCDI.Service;

namespace MyIOCDI
{
    class Program
    {
        static void Main(string[] args)
        {
            ITianYaIOCContainer container = new TianYaIOCContainer();
            {
                //注册
                container.Register<ITestServiceA, TestServiceA>(); //将ITestServiceA注册到TestServiceA
                container.Register<ITestServiceB, TestServiceB>();
                container.Register<ITestServiceB, TestServiceB>(shortName: "ServiceB");
                container.Register<ITestServiceC, TestServiceC>();
                container.Register<ITestServiceD, TestServiceD>(paraList: new object[] { "浪子天涯", 666 }, lifetimeType: LifetimeType.Singleton);

                ITestServiceD d1 = container.Resolve<ITestServiceD>(); //创建对象交给IOC容器
                ITestServiceD d2 = container.Resolve<ITestServiceD>();
                d1.Show();
                Console.WriteLine($"object.ReferenceEquals(d1, d2) = {object.ReferenceEquals(d1, d2)}");
            }

            Console.ReadKey();
        }
    }
}
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运行结果如下:

生命周期为作用域的,其实就是子容器单例,如下所示:

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using System;

using TianYaSharpCore.IOCDI.CustomContainer;
using MyIOCDI.IService;
using MyIOCDI.Service;

namespace MyIOCDI
{
    class Program
    {
        static void Main(string[] args)
        {
            ITianYaIOCContainer container = new TianYaIOCContainer();
            //{
            //    //注册
            //    container.Register<ITestServiceA, TestServiceA>(); //将ITestServiceA注册到TestServiceA
            //    container.Register<ITestServiceB, TestServiceB>();
            //    container.Register<ITestServiceB, TestServiceB>(shortName: "ServiceB");
            //    container.Register<ITestServiceC, TestServiceC>();
            //    container.Register<ITestServiceD, TestServiceD>(paraList: new object[] { "浪子天涯", 666 }, lifetimeType: LifetimeType.Singleton);

            //    ITestServiceD d1 = container.Resolve<ITestServiceD>(); //创建对象交给IOC容器
            //    ITestServiceD d2 = container.Resolve<ITestServiceD>();
            //    d1.Show();
            //    Console.WriteLine($"object.ReferenceEquals(d1, d2) = {object.ReferenceEquals(d1, d2)}");
            //}

            {
                //生命周期:作用域
                //就是Http请求时,一个请求处理过程中,创建都是同一个实例;不同的请求处理过程中,就是不同的实例;
                //得区分请求,Http请求---Asp.NetCore内置Kestrel,初始化一个容器实例;然后每次来一个Http请求,就clone一个,
                //或者叫创建子容器(包含注册关系),然后一个请求就一个子容器实例,那么就可以做到请求单例了(其实就是子容器单例)
                //主要可以去做DbContext  Repository
                container.Register<ITestServiceA, TestServiceA>(lifetimeType: LifetimeType.Scope);
                ITestServiceA a1 = container.Resolve<ITestServiceA>();
                ITestServiceA a2 = container.Resolve<ITestServiceA>();

                Console.WriteLine(object.ReferenceEquals(a1, a2)); //T

                ITianYaIOCContainer container1 = container.CreateChildContainer();
                ITestServiceA a11 = container1.Resolve<ITestServiceA>();
                ITestServiceA a12 = container1.Resolve<ITestServiceA>();

                ITianYaIOCContainer container2 = container.CreateChildContainer();
                ITestServiceA a21 = container2.Resolve<ITestServiceA>();
                ITestServiceA a22 = container2.Resolve<ITestServiceA>();

                Console.WriteLine(object.ReferenceEquals(a11, a12)); //T
                Console.WriteLine(object.ReferenceEquals(a21, a22)); //T

                Console.WriteLine(object.ReferenceEquals(a11, a21)); //F
                Console.WriteLine(object.ReferenceEquals(a11, a22)); //F
                Console.WriteLine(object.ReferenceEquals(a12, a21)); //F
                Console.WriteLine(object.ReferenceEquals(a12, a22)); //F
            }

            Console.ReadKey();
        }
    }
}
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运行结果如下:

至此本文就全部介绍完了,如果觉得对您有所启发请记得点个赞哦!!!

 

Demo源码:

链接:https://pan.baidu.com/s/15xpmWbEDbkm7evpr4iIZNg 
提取码:ckes

此文由博主精心撰写转载请保留此原文链接:https://www.cnblogs.com/xyh9039/p/13663808.html

版权声明:如有雷同纯属巧合,如有侵权请及时联系本人修改,谢谢!!!


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