我们已经实现了用户注册功能，现在想增加日志记录功能。具体来讲就是在用户注册前后，分别输出一条日志。我们当然可以修改原有的业务代码。
现在换个角度来问两个问题：
1. 团队开发中，我们很可能根本拿不到源代码，那又怎么去增加这个功能呢？
2. 这次需求是增加日志，以后再增加其他需求（比如异常处理），是不是仍然要改业务类呢？
总结一下：
我们要在不修改原有类业务代码的前提下，去做类的增强。我们的设计要符合面向对象的原则：对扩展开放，对修改封闭！
都有哪些办法呢？我们尝试以下几种方法：
上次我们使用unity实现了log日志的增强，这次我们来实现异常处理、权限验证两个需求；并且不使用拦截器的方式，而是使用Attribute给原有业务类来打标签的方式来达到业务增强的目的。
原有业务类
业务模型
namespace testAopByDecorator
{
public class User
{
public string Name { get; set; }
public int Id { get; set; }
}
}接口设计
namespace testAopByDecorator
{
public interface IUserProcessor
{
void RegisterUser(User user);
}
}业务实现
using System;
namespace testAopByDecorator
{
public class UserProcessor : IUserProcessor
{
public void RegisterUser(User user)
{
if (user == null)
{
return;
}
Console.WriteLine(string.Format("注册了一个用户{0}：{1}", user.Id, user.Name));
}
}
}上层调用
using System;
namespace testAopByDecorator
{
class Program
{
private static User user = new User { Id = 1, Name = "滇红" };
static void Main(string[] args)
{
Register();
Console.ReadKey();
}
private static void Register()
{
IUserProcessor processor = new UserProcessor();
processor.RegisterUser(user);
}
}
}使用Unity做类的增强
我们将使用第三方的Unity来对原有的类做业务增强，首先使用NuGet安装。 
日志Attribute类
using System;
using Microsoft.Practices.Unity;
using Microsoft.Practices.Unity.InterceptionExtension;
namespace testAopByUnityAttribute
{
public class LogHandlerAttribute : HandlerAttribute
{
public override ICallHandler CreateHandler(IUnityContainer container)
{
ICallHandler handler = new UserProcessorLog { Order = this.Order };
return handler;
}
}
public class UserProcessorLog : ICallHandler
{
public int Order { get; set; }
public IMethodReturn Invoke(IMethodInvocation input, GetNextHandlerDelegate getNext)
{
User user = input.Inputs[0] as User;
before(user);
InvokeHandlerDelegate delegateMethod = getNext();
IMethodReturn returnMessag = delegateMethod(input, getNext);
after(user);
return returnMessag;
}
private void after(User user)
{
Console.WriteLine("日志结束：" + user.Name);
}
private void before(User user)
{
Console.WriteLine("日志开始：" + user.Name);
}
}
}
异常Attribute类
using System;
using Microsoft.Practices.Unity;
using Microsoft.Practices.Unity.InterceptionExtension;
namespace testAopByUnityAttribute
{
public class ExceptionHandlerAttribute : HandlerAttribute
{
public override ICallHandler CreateHandler(IUnityContainer container)
{
ICallHandler handler = new UserProcessorException { Order = this.Order };
return handler;
}
}
public class UserProcessorException : ICallHandler
{
public int Order { get; set; }
public IMethodReturn Invoke(IMethodInvocation input, GetNextHandlerDelegate getNext)
{
User user = input.Inputs[0] as User;
before(user);
InvokeHandlerDelegate delegateMethod = getNext();
IMethodReturn returnMessag = delegateMethod(input, getNext);
if (returnMessag.Exception != null)
{
Console.WriteLine("捕获了异常：" + returnMessag.Exception.Message);
returnMessag.Exception = null; //结束异常栈
}
after(user);
return returnMessag;
}
private void after(User user)
{
Console.WriteLine("异常捕获后：" + user.Name);
}
private void before(User user)
{
Console.WriteLine("异常捕获前：" + user.Name);
}
}
}
权限Attribute类
using System;
using Microsoft.Practices.Unity;
using Microsoft.Practices.Unity.InterceptionExtension;
namespace testAopByUnityAttribute
{
public class AuthorizeHandlerAttribute : HandlerAttribute
{
public override ICallHandler CreateHandler(IUnityContainer container)
{
ICallHandler handler = new UserProcessorAuthorize { Order = this.Order };
return handler;
}
}
public class UserProcessorAuthorize : ICallHandler
{
public int Order { get; set; }
public IMethodReturn Invoke(IMethodInvocation input, GetNextHandlerDelegate getNext)
{
User user = input.Inputs[0] as User;
Console.WriteLine("权限验证中......");
if(user == null || !user.Name.Equals("admin"))
{
//抛出异常
return input.CreateExceptionMethodReturn(new Exception("没有这个用户！"));
}
before(user);
InvokeHandlerDelegate delegateMethod = getNext();
IMethodReturn returnMessage = delegateMethod(input, getNext);
after(user);
return returnMessage;
}
private void after(User user)
{
Console.WriteLine("用户注册后：" + user.Name);
}
private void before(User user)
{
Console.WriteLine("用户注册前：" + user.Name);
}
}
}
给业务接口打标签，原有业务类会自动继承
namespace testAopByUnityAttribute
{
//使用Order来决定特性的执行时序
[ExceptionHandler(Order =1)]
[LogHandler(Order = 2)]
[AuthorizeHandler(Order =3)]
public interface IUserProcessor
{
void RegisterUser(User user);
}
}
上层调用
using Microsoft.Practices.Unity;
using Microsoft.Practices.Unity.InterceptionExtension;
using System;
namespace testAopByUnityAttribute
{
class Program
{
private static User user = new User { Id = 1, Name = "admin" };
static void Main(string[] args)
{
RegisterAndLog();
Console.ReadKey();
}
private static void RegisterAndLog()
{
//创建容器
IUnityContainer container = new UnityContainer();
//注册服务
container.RegisterType<IUserProcessor, UserProcessor>();
//扩展拦截器
container.AddNewExtension<Interception>().Configure<Interception>()
.SetInterceptorFor<IUserProcessor>(new InterfaceInterceptor());
//调用服务
IUserProcessor processor = container.Resolve<IUserProcessor>();
try
{
processor.RegisterUser(user);
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
}
}
对比一下扩展前后的业务展现
