Manage software dependencies with ioc and aop
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The document discusses managing software dependencies through inversion of control (IoC) and aspect-oriented programming (AOP). It describes how dependencies can make software rigid, fragile, and difficult to maintain. It then shows how to decouple dependencies using IoC patterns like dependency injection and AOP to address cross-cutting concerns.
![Manage software dependencies with IoC and AOP Stefano Leli 14° Workshop DotNetMarche Friday 16 th April 2010 @sleli [email_address]](https://image.slidesharecdn.com/managesoftwaredependencieswithiocandaop-100525081217-phpapp02/85/Manage-software-dependencies-with-ioc-and-aop-1-320.jpg)
![Service Locator class ServiceLocator { /* Singleton instance */ private static ServiceLocator _instance; public static void Load(ServiceLocator arg) { _instance = arg; } /* Storing and Retrieve services */ private Dictionary<string, Object> _services = new Dictionary<string, Object>(); public Object RegisterService(String key) { return _instance._services[key]; } public static void Lookup(String key, Object service) { _services.Add(key, service); } }](https://image.slidesharecdn.com/managesoftwaredependencieswithiocandaop-100525081217-phpapp02/85/Manage-software-dependencies-with-ioc-and-aop-21-320.jpg)
Manage software dependencies with ioc and aop
- 1. Manage software dependencies with IoC and AOP Stefano Leli 14° Workshop DotNetMarche Friday 16 th April 2010 @sleli [email_address]
- 2. Software Dependencies Service Locator Inversion of Control Dependency Injection Aspect Oriented Programming Agenda
- 3. What is a Dependency?
- 4. Dependencies public RequestService() { ClassB b = new ClassB() b.DoService(); } dependent +DoService() ClassA +RequestService() ClassB
- 5. Layer Dependencies High-level modules should not depend on low-level modules. Both should depend on abstractions Robert C. Martin Presentation Layer Business Layer Data Access Layer Depends on DB Depends on Depends on
- 6. Why dependencies are evil? Tight coupling of software components hard to change because every change affects too many other parts of the system (Rigidity) When you make a change, unexpected parts of the system break. (Fragility) hard to reuse in another application. (Immobility) Software becomes hard to maintain Difficult to isolate when testing
- 7. Scenario
- 8. Copier Example Copier + PerformCopy() Keyboard + ReadFromKB(c : char ) Video + WriteToVideo () : char
- 9. class Copier { Keyboard _reader; Video _writer; public Copier() { _reader = new Keyboard(); _writer = new Video(); } public void PerformCopy() { int chr; while ( (chr = _reader.ReadFromKeyboard() ) != '\r') _writer.WriteToVideo(chr); } } Copier Example class Keyboard { public int ReadFromKeyboard() { return Console.ReadKey(true).KeyChar; } } class Video { public void WriteToVideo(int chr) { Console.Write((char)chr); } }
- 10. class Copier { Keyboard _reader; Video _writer; public Copier() { _ reader = new Keyboard(); _writer = new Video(); } public void PerformCopy() { int chr; while ( (chr = _reader.ReadFromKeyboard() ) != '\r') _writer.WriteToVideo(chr); } } Copier Example class Keyboard { public int ReadFromKeyboard() { return Console.ReadKey(true).KeyChar; } } class Video { public void WriteToVideo(int chr) { Console.Write((char)chr); } } Problem
- 11. Program to an interface, not an implementation
- 12. Copier Example <<create>> <<create>> Concrete class should depend on abstraction Robert Martin IWriter IReader Copier + PerformCopy() Keyboard + Read(c : char ) Video + Write () : char
- 13. class Copier { IReader _reader; IWriter _writer; public Copier() { _reader = new Keyboard(); _writer = new Video(); } public void PerformCopy() { int chr; while ( (chr = _reader.Read() ) != '\r') _writer.Write(chr); } } Copier Example class Keyboard : IReader { public int Read () { return Console.ReadKey(true).KeyChar; } } class Video : IWriter { public void Write (int chr) { Console.Write((char)chr); } }
- 14. class Copier { IReader _reader; IWriter _writer; public Copier() { _reader = new Keyboard(); _writer = new Video(); } public void PerformCopy() { int chr; while ( (chr = _reader.Read() ) != '\r') _writer.Write(chr); } } Copier Example class Keyboard : IReader { public int Read () { return Console.ReadKey(true).KeyChar; } } class Video : IWriter { public void Write (int chr) { Console.Write((char)chr); } } Problem Dependencies resolution is still here!!!
- 16. <<create>> Using a Factory <<create>> Copier + Copier(r : IReader, w : IWriter) + PerformCopy() IWriter IReader Keyboard + Read(c : char ) Video + Write () : char ReaderFactory + GetInstance() : IReader WriterFactory + GetInstance() : IWriter
- 17. class Copier { IReader _reader; IWriter _writer; public Copier() { _ reader = ReaderFactory. GetInstance (); _writer = WriterFactory. GetInstance (); } public void PerformCopy() { int chr; while ( (chr = _reader.Read() ) != '\r') _writer.Write(chr); } } Using a Factory class ReaderFactory { public static IReader GetInstance() { return new Keyboard(); } } class WriterFactory { public static IWriter GetInstance() { return new Video(); } }
- 18. class Copier { IReader _reader; IWriter _writer; public Copier() { _reader = ReaderFactory. GetInstance (); _writer = WriterFactory. GetInstance (); } public void PerformCopy() { int chr; while ( (chr = _reader.Read() ) != '\r') _writer.Write(chr); } } Using a Factory class ReaderFactory { public static IReader GetInstance() { return new Keyboard(); } } class WriterFactory { public static IWriter GetInstance() { return new Video(); } } We have just moved the problem!!! Problem
- 19. Service Locator << create >> <<create>> Copier + PerformCopy() ServiceLocator +Lookup() : Object +RegisterService(o : Object) _instance : ServiceLocator … IWriter IReader Keyboard + Read(c : char ) Video + Write () : char
- 20. Service Locator << create >> <<create>> Copier + PerformCopy() ServiceLocator +Lookup() : Object +RegisterService(o : Object) _instance : ServiceLocator … IWriter IReader Keyboard + Read(c : char ) Video + Write () : char
- 21. Service Locator class ServiceLocator { /* Singleton instance */ private static ServiceLocator _instance; public static void Load(ServiceLocator arg) { _instance = arg; } /* Storing and Retrieve services */ private Dictionary<string, Object> _services = new Dictionary<string, Object>(); public Object RegisterService(String key) { return _instance._services[key]; } public static void Lookup(String key, Object service) { _services.Add(key, service); } }
- 22. Service Locator class Copier { IReader _reader; IWriter _writer; public Copier() { _reader = (IReader)ServiceLocator.Lookup("reader"); _writer = (IWriter)ServiceLocator.Lookup("writer"); ; } public void PerformCopy() { int chr; while ( (chr = _reader.Read() ) != '\r') _writer.Write(chr); } } /* Configure Service Locator method */ private void configureLocator() { ServiceLocator locator = new ServiceLocator(); locator.LoadService("reader", new Keyboard()); locator.LoadService("writer", new Video()); ServiceLocator.Load(locator); }
- 23. Pro Help to avoid coupling Centralize dependencies resolution Cons Introduce dependencies with the locator Difficult to test Service Locator
- 24. I nversion o f C ontrol
- 25. Inversion of Control , or IoC , is an abstract principle describing an aspect of some software architecture designs in which the flow of control of a system is inverted in comparison to traditional programming. Hollywood Principle “ don't call us, we'll call you.” There are many implementations of IoC, Dependency Injections is one of there. What is IoC?
- 26. Technique for supplying an external dependency to a software component. Implemented by a Container (IoC) Creates and assembles component/objects and manages their lifecycle Generally configured by coding or external file Three forms of injection Constructor Injection Setter Injection Interface Injection What is Dependency Injection?
- 27. IoC Container Copier + Copier(r : IReader, w : IWriter) + PerformCopy() IWriter IReader Keyboard + Read(c : char ) Video + Write () : char
- 28. << create >> <<create>> IoC Container <<create>> Copier + Copier(r : IReader, w : IWriter) + PerformCopy() XML Config IWriter IReader Keyboard + Read(c : char ) Video + Write () : char IoCContainer …
- 29. DI: Constructor Injection class Copier { IReader _reader; IWriter _writer; public Copier( IReader reader, IWriter writer ) { _reader = reader; _writer = writer; } public void PerformCopy() { int chr; while ( (chr = _reader.Read() ) != '\r') _writer.Write(chr); } } To prefer in case of Mandatory Dependencies
- 30. DI: Setter Injection class Copier { private IReader _reader; public IReader Reader { set{_reader = value;} } private IWriter _writer ; public IWriter Writer { set{_writer = value;} } public void PerformCopy() { int chr; while ((chr = _reader.Read()) != '\r') _writer.Write(chr); } } To prefer in case of Optional Dependencies
- 31. DI: Interface Injection class Copier { private IReader _reader; public void InjectReader(IReader reader) { _reader = reader; } private IWriter _writer; public void InjectWriter(IWriter writer) { _writer = writer; } public void PerformCopy() { int chr; while ((chr = _reader.Read()) != '\r') _writer.Write(chr); } } interface IReaderInject { void injectReader(IReader reader); } interface IWriterInject { void injectWriter(IWriter reader); } Quite Never Used
- 32. Pro High Decoupling level Completely transparent to the Domain Model High Configurable Integrated with lots of framework Cons Difficult to understand by newbie Complex to debug DI: Consideration
- 33. A spect O riented P rogramming
- 34. AOP is a programming paradigm AOP is a new way of thinking about software design Enhance OOP in separating concerns to improve modularization OOP modularizes concerns AOP addresses cross-cutting concerns What is AOP?
- 35. Separation of Concern Searching Booking Payment
- 36. Separation of Concern Reduce software complexity Limit the impact of change Facilitate reuse Simplify components integration Booking Payment Searching OOP Searching Booking Payment
- 37. Crosscutting Concern Crosscutting concerns are functionalities that span multiple modules Security Logging Transaction Management … Hard to model with traditional OOP approach Code Scattering Code Tangling Booking Security Logging Payment Security Logging Searching Security Logging OOP Crosscutting Concerns Searching Booking Payment
- 38. Crosscutting Concern Booking Payment Searching Security Logging AOP Booking Security Logging Payment Security Logging Searching Security Logging OOP Crosscutting Concerns Searching Booking Payment
- 39. How it works… Object_B Object_A Object Oriented Flow
- 40. How it works… Aspect Object_B Object_A advice Object Oriented Flow Aspect Oriented Flow pointcut = method_B Target Object = Object_B jointpoint = method invocation
- 41. How it works… Aspect Equivalent to class in OOP Used to describe a Crosscutting Concern Aspect Object_B Object_A advice Object Oriented Flow Aspect Oriented Flow pointcut = method_B Target Object = Object_B jointpoint = method invocation
- 42. How it works… Join Point Well-defined point during the execution of a program (e.g. method invocation, attribute access, exception handling,…) Aspect Object_B Object_A advice Object Oriented Flow Aspect Oriented Flow pointcut = method_B Target Object = Object_B jointpoint = method invocation
- 43. How it works… Advice action taken by an aspect at a particular join point Aspect Object_B Object_A advice Object Oriented Flow Aspect Oriented Flow pointcut = method_B Target Object = Object_B jointpoint = method invocation
- 44. How it works… Pointcut Predicate that matches join points Advice is associated with a pointcut expression and runs at any join point matched by the pointcut Aspect Object_B Object_A advice Object Oriented Flow Aspect Oriented Flow pointcut = method_B Target Object = Object_B jointpoint = method invocation
- 45. How it works… Target Object Also called Advised Object Object being advised by one or more aspects Aspect Object_B Object_A advice Object Oriented Flow Aspect Oriented Flow pointcut = method_B Target Object = Object_B jointpoint = method invocation
- 46. Weaving Run-Time Weaving Compile-Time Weaving … behind the scenes Aspect Object_B Object_A advice Object Oriented Flow Aspect Oriented Flow pointcut = method_B Target Object = Object_B jointpoint = method invocation Weaving
- 47. References Martin Fowler Inversion of Control Containers and the Dependency Injection pattern Robert C. Martin The Dependency Inversion Principle AOP Alliance
- 48. Questions?
- 49. Slide and Materials www.dotnetmarche.org Grazie!