AspectJ2EE/Clasa Israel Institute of Technology The Computer Science department Itay Maman

2 Talk outline  Our Group  Overview of AspectJ2EE Weaving mechanism  The Clasa language  A generic middleware platform: The vision

3 Overview of AspectJ2EE  The key issue: Weaving can be achieved via sub-classing The sub-class will inject the additional code into its super class Each aspect is actually a type-to-subtype mapping Hence, aspects in AspectJ2EE are called: Shakeins Objects must be created through an object factory  (the dynamic type of the object is different from its static type)

4 AspectJ2EE: What the System Generates (Assumes 4 Applied aspects) Lifecycle management is an aspect

5 Current focus: Clasa (1/4) Motivation  Describing the characteristic of a class is not an easy task  Example 1- Let ’ s define a stateless class as a class with no fields. Can it have static fields? Can its super class have a private instance field?  Example 2- NoName is a class without a “ getName() ” method Can it have a static getName() method? Can its super class have a private non-static getName() method?

6 Current focus: Clasa (2/4) Motivation (continued)  There is a major gap between the intuition and the formal definition  This gap must be bridged when: Statistical analysis is applied over classes A refactoring tool is developed A point-cut is defined …  Current point-cut constructs lack in their expressive power Thus, they cannot capture the wide spectrum of Java element

7 Current focus: Clasa (3/4) What is Clasa?  A language over the domain of Java programs A Jar file can be thought of as a database A Clasa function can be thought of as a query  Main features Built-in functions for handling relations Pattern matching Elegant syntax Static, strong typing, with type inference  Implementation is based on ideas drawn from languages such as Icon, Prolog  By using Clasa, one can precisely define complex pointcuts

8 Current focus: Clasa (4/4) Some Clasa queries has_age := abstract class { public int getAge(); public void setAge(int); } primitive := boolean | char | int | long | float | double; serializeable := primitive | implements: { ‘java.lang.Serializeable‘) non_private_ctor := [public|protected|default] ctor; singleton := class { no non_private_ctor; static T create(); private static T field; }

9 Generic middleware platform (GMF) 1/4 1 st approach  What AspectJ2EE needs? An infrastructure which provides core J2EE services:  Persistency  Security  Transaction  Logging  … The protocol should be minimal but complete  No fancy (compound) operations  Just like the APIs provided by an operating system

10 (1 st approach continued)  What AspectJ2EE does not need? AspectJ2EE ’ s weaver is based on inheritance  The advice is woven by means of sub-classing  sub-classing is a built-in mechanism of Java =>No “ Aspect awareness ” : Neither the GMF nor the JVM need to support aspects  A “ nice to have ” feature: GMF will allow client code to customize the type of each created object Can be thought of as a built-in object factory Increases POJOness of the code Generic middleware platform (GMF) 2/4

11 2 nd approach  Let ’ s think of the GMF abstractly … 1. Provides a set of built-in aspects 2. Allows developers to define new aspects 3. Is implemented by aspects ?! => one aspect-weaving mechanism that is used both internally and externally  Pros Small, compact core A Highly customizable GMF  Cons Bootstrapping Not specifically related to middleware platforms Performance Generic middleware platform (GMF) 3/4

12 (2 nd approach continued)  What is the minimal kernel of such a GMF? A Pointcut matching engine “ primitive ” aspect: Object creation  The type-to-subtype mapping is just a parameter “ primitive ” aspect: System configuration change  The bottom line: A small kernel A huge library Almost every thing can be customized Generic middleware platform (GMF) 4/4

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