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Automating Crosscutting Modification

Automating Crosscutting Modification. By Michael Kleyman. When AOP is Used?. It is usually said that aspects represent crosscutting concerns. No clear definition of such a concern. AOP can be dangerous when overused. Trivial Examples. Logging Authorization. Telecom Example.

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Automating Crosscutting Modification

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  1. Automating Crosscutting Modification By Michael Kleyman

  2. When AOP is Used? • It is usually said that aspects represent crosscutting concerns. • No clear definition of such a concern. • AOP can be dangerous when overused.

  3. Trivial Examples • Logging • Authorization

  4. Telecom Example • Calls, messaging etc. are the core concepts • Represented by classes, such as Call or Connection • Billing is the crosscutting concern, represented by an aspect. • Payment calculation initiated in advices to methods of the core classes.

  5. When AOP is helpful, but not used • Corporate policies do not allow use of experimental, immature technologies • An aspect allows rapid modification of existing code, but the resulting program structure is not the best possible structure • Crosscutting modification as opposed to crosscutting concern

  6. Example: Object Pooling • Goal: reuse objects instead of creating new ones • Can be represented by a factory class. • Introducing object pooling into existing system is difficult. • AspectJ allows an easy but controversial solution

  7. What is ACME • Convert AspectJ solution to pure Java • Prove of concept • Based on specific examples • Additional examples may be covered later

  8. Key Goals • Java code must produce exactly the same results as the aspect code. • Java code should not be significantly longer than the aspect code. • The produced code should be easily modified and used.

  9. Key Goals (Continued) • The generated code must look similar to code written by a human programmer. • Based on commonly used patterns and idioms.

  10. ACME vs. AspectJ Compiler • Must not support the entire language • Must generate meaningful names (possibly with user’s help) • May not use some complicated structures used in the compiler.

  11. Workflow with ACME • Implement the required modification using aspects • Test the implementation • When the result is satisfactory, run ACME to generate pure Java code with same functionality

  12. Creating Singleton Class • Aspect interacts with other code through pointcuts on functions of a single class. • Aspect is converted to a class automatically. • All calls that are advised by the aspect are replaced by calls to the singleton. • Example: object pooling.

  13. Inlining Aspect Code • Aspect may be used to modify both interface and behavior of an existing class. • Involves both advises and inter-type member declarations. • Example: modification of the Point class. • Example: introduction of transactions

  14. Automatic Modification • Add the member introduced by the inter-type declaration to the class • Add a function for each advice • Replace all calls advised by the aspect by calls to the new functions

  15. Aspect Hierarchies • Allow code reuse in several aspects • Typically involve abstract pointcuts and concrete implementation of the advices • Transformed into hierarchies of classes where the leaves are implemented as singletons.

  16. When ACME helps? • Evolution aid: test before changing the system. • Refactoring • Eases adoption of aspect technology

  17. When not? • Aspect represent crosscutting concerns • Aspects used as a configuration tool for different application of the system

  18. Unsupported Language Features • Wildcards • Type-dependent pointcut definitions • Implicit type casting • Compile-time applications of aspects, such as “declare error” • Execution pointcuts

  19. More on execution join points • Require replacing the implementation of functions, not the calls to them. • With inheritance require replacing several functions for each advice. • Anything but the simplest around advice must be transformed to very complicated code • Very limited benefit

  20. Case Study • ACME was applied to Shay Raz’s work on system scaling with aspects. • Some aspects required cosmetic changes before processing. • Some can not be processed because they involve implicit type casting. • Possible solution: rewrite the aspects, removing abstract pointcuts from the base aspect.

  21. Implementation Details • Built as an Eclipse plugin • Uses JDT library for Java source manipulation • There is no such library for AspectJ code

  22. Algorithm Steps • Parse the AspectJ files • Create new classes for “singleton” aspects. • Add new members to existing classes • Find advised function calls (using JDT) • Replace these calls by calls to generated functions

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