Introduction to aop
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The document introduces aspects-oriented programming (AOP) as a way to separate cross-cutting concerns from core functionality in code. It discusses problems with duplicating code for logging, validation, and other concerns across classes. The solutions section evaluates different AOP approaches: 1) using higher-order functions, 2) dynamic proxies through dependency injection containers, 3) modifying bytecode through IL transformations, and 4) compile-time modifications. While each approach has advantages, build-time AOP frameworks avoid low-level bytecode work while still providing powerful code transformations.
Introduction to aop
- 1. Introduction to AOP Dror Helper @dhelper
- 2. About.Me Software developer and technical lead PostSharp MVP Blogger: http://blog.drorhelper.com
- 3. Developer write code void transfer(Account fromAcc, Account toAcc, int amount) { if (fromAcc.getBalance() < amount) { throw new InsufficientFundsException(); } fromAcc.withdraw(amount); toAcc.deposit(amount); }
- 4. Permission support – Right away! void transfer(Account fromAcc, Account toAcc, int amount, User user) { if (! checkUserPermission(user)) { throw new UnauthorizedUserException(); } if (fromAcc.getBalance() < amount) { throw new InsufficientFundsException(); } fromAcc.withdraw(amount); toAcc.deposit(amount); }
- 5. Need to check parameters – Done! void transfer(Account fromAcc, Account toAcc, int amount, User user) { if(fromAcc == null || toAcc == null) { throw new IllegalArgumentException (); } if(balance <= 0) { throw new IllegalArgumentException (); } if (! checkUserPermission(user)) { throw new UnauthorizedUserException(); } if (fromAcc.getBalance() < amount) { throw new InsufficientFundsException(); } fromAcc.withdraw(amount); toAcc.deposit(amount); }
- 6. Needs logging – no problems! void transfer(Account fromAcc, Account toAcc, int amount, User user) { logger.info("transferring money..."); if(balance <= 0) { throw new IllegalArgumentException (); } if (! checkUserPermission(user)) { logger.info("User has no permission."); throw new UnauthorizedUserException(); } if (fromAcc.getBalance() < amount) { logger.info("Insufficient Funds, sorry"); throw new InsufficientFundsException(); } fromAcc.withdraw(amount); toAcc.deposit(amount);
- 7. And finally – exception handling void transfer(Account fromAcc, Account toAcc, int amount, User user) { logger.info("transferring money..."); if(balance <= 0) { throw new IllegalArgumentException (); } if (! checkUserPermission(user)) { logger.info("User has no permission."); throw new UnauthorizedUserException(); } if (fromAcc.getBalance() < amount) { logger.info("Insufficient Funds, sorry"); throw new InsufficientFundsException(); } try { fromAcc.withdraw(amount); toAcc.deposit(amount); } catch(Exception exc) { logger.info(“failed transaction."); return; }
- 8. What can we do?
- 9. The Problem Code duplication Hard to read Difficult to maintain Not all programmers code the same Ctrl + C, Ctrl + V
- 10. Problem - Cross cutting concerns Customer Product Order Logging Cross-Cutting Security Concerns Caching
- 11. Non-Functional Requirements Security Caching Tracing Exception handling Monitoring Validation Persistence Transactions Thread sync
- 12. Solution AOP Separation of concerns Extension of OOP 1. Encapsulate Cross cutting concerns into aspects 2. Apply aspects to code
- 13. Why AOP • AOP exist for more then 15 Mature years Industry • Industry standard adopted Observed • -15% lines of code Benefits • -20% decoupling
- 14. Terminology
- 15. Join Point static void Main() { myClass1.Func1 var myClass1 = new MyClass(); var myClass2 = new MyClass(); myClass1.Func1(); myClass1.Func2(2, 3); myClass1.Func2 myClass2.Func2(4, 5); } myClass2.Func2
- 16. Point Cuts myClass1.Func1 myClass1.Func2 Before Func2 myClass2.Func2
- 17. Advice The code to run Typically small Injected at join point
- 18. Aspect Join Point + Advice = Aspect
- 19. How to “do” AOP
- 20. Our example for today – the calculator
- 22. #1 Functional programming Using higher order functions to “warp” existing code Decorator pattern
- 23. 1# Functional Programming + - No additional You cannot automatically dependency in your pass context from the caller to the aspect code build or runtime code. Must modify the code of Programmers are every method to which already familiar with the you want to add the technology. aspect. Aspect composition is less convenient.
- 24. Why not use existing tools
- 25. What IoC containers can do for you? Enable Dependency Injection (DI) Create objects and satisfy it’s dependencies A lot more..
- 26. #2 Dynamic proxies Framework Application Proxy Aspect Object
- 27. .NET IoC tools Unity http://unity.codeplex.com/ Spring.NET http://www.springframework.net/ Castle http://www.castleproject.org/
- 28. Dynamic proxies + - You may already be Very limited aspect-oriented features. using a DI framework. Your objects must be instantiated using the Aspects can be container configured after build. Does not work on static, non-public, and/or Some aspects may be non-virtual methods provided by the Does not work on framework. fields, properties, or events.
- 29. #3 MSIL transformations IL Final Code Compile weaving Assembly
- 30. IL transformation tools Mono.Cecil http://www.mono-project.com/Cecil NotifyPropertyWeaver http://code.google.com/p/notifypropertyweaver/
- 31. MSIL transformations + - Very powerful. You can Requires an advanced knowledge of MSIL. achieve virtually any code transformation Very low level These frameworks are typically do not compose well when many are free of charge and applied to the same backed by large method. companies. No Visual Studio tooling.
- 32. #4 Build time AOP Build Process Intermediate Final Source Compiler Assembly AOP Assembly Code (IL) Aspects
- 33. Summery Use AOP because: Less code = fewer bugs Less code = easier to read and maintain Reduce duplicate code Improve team work/architecture Reduce development cost
- 34. Resources Cross Cutting Concerns blog http://crosscuttingconcerns.com/ My blog: http://blog.drorhelper.com
Editor's Notes
- #11: Non functional requirments
- #16: A call to a methodThe method’s executionAssignment to a variableReturn statementObject constructionConditional checkComparisonException handlerLoops
- #17: A group of Join pointFilter drivenAttribute driven
- #25: IoC containers
- #27: Using IoC containers
- #30: Add IL in compile timeDifficult and fragile“Mini AOPs”
- #33: Adding step to compilationUsing IL weavingShow diagram