一个简单的AOP框架学习
在.Net Unity2.0中的Interception，按三种方式实现:
1.TransparentProxy/RealProxy Interceptor 即Remoting代理机制。
2.Interface Interceptor 即动态代码 （Emit编程)实现
3.Virtual Method Interceptor 也是动态代码实现，Emit编程基本类似于IL编程了。
实例拦截与类型拦截
1.实例拦截
TransparentProxy 与 Interface Interceptor 属于实例拦截，所谓实例拦截就是被拦截对象完整而独立的在内参中存在。Client端通过代理类与被拦截对象发生通信（方法调用）。
2.类型拦截
Virtual Method 方式属于类型拦截，内参中不存在被拦截类型的实例，拦截框架通过动态代码生成被拦截类型的子类型程序集，该程序集被加载后对应的子类型被实例化于内存中与Client发生通信
下面针对TransparentProxy/RealProxy 与 Interface Interceptor帖出手头上dll实现的代码
1.TransparentProxy/RealProxy实现
using System.Reflection;
using System.Runtime.Remoting.Proxies;
using System.Runtime.Remoting.Messaging;
using System.Runtime.Remoting;
internal class TransparentProxy : RealProxy
{
// Fields
private readonly MarshalByRefObject m_Target;
// Methods
public TransparentProxy(MarshalByRefObject target)
: base (target.GetType())
{
this .m_Target = target;
}
public static object GetProxy(MarshalByRefObject target)
{
TransparentProxy proxy = new TransparentProxy(target);
return proxy.GetTransparentProxy();
}
public override IMessage Invoke(IMessage msg)
{
IMessage message = null ;
IMethodCallMessage callMsg = msg as IMethodCallMessage;
if (callMsg != null )
{
object [] customAttributes = callMsg.MethodBase.GetCustomAttributes( true );
this .InvokeBeforeAttribute(customAttributes, callMsg);
try
{
message = RemotingServices.ExecuteMessage( this .m_Target, callMsg);
}
catch (Exception exception)
{
this .InvokeExceptionAttribute(customAttributes, callMsg, exception);
throw ;
}
this .InvokeAfterAttribute(customAttributes, callMsg, ((ReturnMessage)message).ReturnValue);
}
return message;
}
//..........
//............
}
类TransproxyProxy中维护着一个到target类实例的引用(必须是MarshalByRefObject类型的子类），最终的方法调用会通过消息机制到达target实例--语句RemotingServices.ExecuteMessage(this.m_Target, callMsg);,在调用目标对象的目标方法之前会调用InvokeBeforeAttribute，错误时会调用InvokeExceptionAttribute,而完成后调用 InvokeAfterAttribute .这里需要注意的是Unity2.0 Interception 中将要调用的InterceptionBehavior构建成管道模型，编程时会有Scop样的开闭结构，而这里的实现只是顺序的调用，这点需要加以区分 。InvokeBeforeAttribute等方法实现如下
private void InvokeAfterAttribute( object [] attributes, IMethodCallMessage callMsg, object result)
{
foreach ( object obj2 in attributes)
{
AfterAttribute attribute = obj2 as AfterAttribute;
if (attribute != null )
{
attribute.Invoke( this .m_Target, callMsg.MethodBase, callMsg.InArgs, result);
}
}
List<IInterception> interceptionList = ProxyBuilder.GetInterceptionList( this .m_Target.GetType().FullName + "." + callMsg.MethodName, InterceptionType.After);
if (interceptionList != null )
{
foreach (IInterception interception in interceptionList)
{
interception.Invoke( this .m_Target, callMsg.MethodBase, callMsg.InArgs, result);
}
}
}
2.Interface Interceptor 代码
public static object GetProxyInstance( object target, Type interfaceType)
{
return Activator.CreateInstance(GetProxyType(target.GetType(), interfaceType), new object [] { target, interfaceType });
}
private static Type GetProxyType(Type targetType, Type interfaceType)
{
AppDomain domain = Thread.GetDomain();
AssemblyName name = new AssemblyName();
name.Name = "TempAssemblyInjection" ;
AssemblyName name2 = name;
AssemblyBuilder assemblyBuilder = domain.DefineDynamicAssembly(name2, AssemblyBuilderAccess.Run);
ModuleBuilder builder = assemblyBuilder.DefineDynamicModule( "TempClassInjection" );
Type type = builder.GetType( "TempAssemblyInjection__Proxy" + interfaceType.Name + targetType.Name);
if (type != null )
{
return type;
}
m_TypeBuilder = builder.DefineType( "TempAssemblyInjection__Proxy" + interfaceType.Name + targetType.Name, TypeAttributes.Public, targetType.BaseType, new Type[] { interfaceType });
m_Target = m_TypeBuilder.DefineField( "target" , interfaceType, FieldAttributes.Private);
m_Interface = m_TypeBuilder.DefineField( "iface" , typeof (Type), FieldAttributes.Private);
CreateConstructor(m_TypeBuilder, m_Target, m_Interface);
foreach (MethodInfo info in interfaceType.GetMethods())
{
CreateProxyMethod(info, m_TypeBuilder);
}
return m_TypeBuilder.CreateType();
}
上面代码通过Emit编程动态构建程序集，程序集中包括一个到目标类的代理类,针对给定接口中的方法签名逐个创建代理方法--语句CreateProxyMethod(info, m_TypeBuilder);
另外可以看到代理类型的程序集只在第一次访问时被创建
--语句
Type type = builder.GetType("TempAssemblyInjection__Proxy" + interfaceType.Name + targetType.Name);
if (type != null)
{
return type;
}
建立的代理类定义类似如下代码:
public class TempAssemblyInjection__ProxyIAnimalDog : IAnimal
{
// Fields
private Type iface;
private IAnimal target;
// Methods
public TempAssemblyInjection__ProxyIAnimalDog( object obj1, Type type1)
{
this .target = (IAnimal) obj1;
this .iface = type1;
}
public override int Run( int num1, int num2)
{
object [] parameters = new object [] { num1, num2 };
return ( int ) DynamicProxy.InterceptHandler( this .target, <BR> Helper.GetMethodFromType( this .target.GetType(), MethodBase.GetCurrentMethod()),<BR> parameters, <BR> Helper.AspectUnion(Helper.GetMethodFromType( this .iface, MethodBase.GetCurrentMethod()).GetCustomAttributes( typeof (AspectAttribute), true ))<BR> );
}
}
DynamicProxy.InterceptHandler的代码
public static object InterceptHandlerMethod( object target, MethodBase method, object [] parameters, AspectAttribute[] attributes)
{
object obj2;
foreach (AspectAttribute attribute in attributes)
{
if (attribute is BeforeAttribute)
{
attribute.Invoke(target, method, parameters, null );
}
}
foreach (IInterception interception in ProxyBuilder.GetInterceptionList(target.GetType().FullName + "." + method.Name, InterceptionType.Before))
{
interception.Invoke(target, method, parameters, null );
}
try
{
obj2 = target.GetType().GetMethod(method.Name).Invoke(target, parameters);
}
catch (Exception exception)
{
foreach (AspectAttribute attribute2 in attributes)
{
if (attribute2 is ExceptionAttribute)
{
attribute2.Invoke(target, method, parameters, exception);
}
}
foreach (IInterception interception2 in ProxyBuilder.GetInterceptionList(target.GetType().FullName + "." + method.Name, InterceptionType.Exception))
{
interception2.Invoke(target, method, parameters, exception);
}
throw ;
}
foreach (AspectAttribute attribute3 in attributes)
{
if (attribute3 is AfterAttribute)
{
attribute3.Invoke(target, method, parameters, obj2);
}
}
foreach (IInterception interception3 in ProxyBuilder.GetInterceptionList(target.GetType().FullName + "." + method.Name, InterceptionType.After))
{
interception3.Invoke(target, method, parameters, obj2);
}
return obj2;
}
// Properties
public static Callback InterceptHandler
{
get
{
return new Callback(DynamicProxy.InterceptHandlerMethod);
}
}
完成代码与使用Demo请下载演示包
================================== 点这里下载 =========================
http://www.cnblogs.com/wdfrog/archive/2011/03/18/1988091.html
作者： Leo_wl
出处： http://www.cnblogs.com/Leo_wl/
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