Aspect Oriented Programming

Transcription

1 Aspect Oriented Programming Why, What and How? Andy Clement AspectJ Committer IBM Hursley Park 1

2 Agenda Why? Why do we need AOP? What? What is AOP? AspectJ How? The need for tool support Demo: AspectJ Development Tools (AJDT) for Eclipse Demo: Using AOP on real middleware Adopting the technology 2

3 Good Modularity: What oo is good at 3 XML parsing in org.apache.tomcat Red shows relevant lines of code Nicely fits in one box

4 Good Modularity: What oo is good at 4 URL pattern matching in org.apache.tomcat Red shows relevant lines of code Nicely fits in two boxes (using inheritance)

5 No Modularity: What oo is bad at 5 Where is logging in org.apache.tomcat? Not in just one place, not even in a small number of places Scattered and tangled

6 The Cost of Tangled Code Redundant code Same fragment of code in many places e.g. Difficult to reason about Non-explicit structure The big picture of the tangling isn t clear Difficult to change Have to find all the code involved And be sure to change it consistently And be sure not to break it by accident 6

7 AO tries to recognize Crosscutting concerns: Are inherent in any complex system Have a clear purpose Have a natural structure Lets capture them explicitly: In a modular way With language and tool support 7 When designing software, the ideal mapping is 1..1: One concept at the design level maps to one class or package (one module) at the code level

8 AspectJ An aspect oriented programming (AOP) language Java language extension Divides system into core concerns (classes) crosscutting concerns (aspects) Broad IDE support Eclipse, Emacs, JBuilder, NetBeans, 8

9 What is an AspectJ Aspect? Aspects are... At the design level concerns that crosscut At the implementation level a programming construct Aspect = pointcut + advice 9

10 What s a Pointcut? Join point An event in the execution of Java program. e.g. Method call, field access, exception handler, object initialization 10 Pointcut Picks out joinpoints in a particular system e.g. call of method foo(), set of field x, constructor for object Fred Can also expose context from the matched join point

11 Types of Pointcuts Event based - well defined execution points, e.g. method calls, executions field gets / sets exception handling object and class initialisation Scoping - only select joinpoints within a certain scope, e.g. within a set of packages, within the implementation of a method, in the control flow of some event (e.g. downstream of an unsecured call) 11 Context matching - expose context at the joinpoint, e.g. identity of the caller identity of the target object exception being handled value being put into a field

12 What s Advice? Advice Java logic to execute when conditions of a pointcut are met. Types of Advice: before() Executes before the joinpoint after() throwing/returning Executes after the joinpoint, execution can be made conditional on how joinpoint exits (i.e. with/without exception) around() Executes instead of the joinpoint has a choice about whether to invoke the original logic 12 Can be parameterized to process context exposed by the pointcut

13 Eclipse is #1 for AOSD AspectJ Development Tools (AJDT) for Eclipse Open Source Developed in Hursley Partnership with AspectJ team Fully tested in WebSphere Studio and Rational Eclipse based tools 13

14 AJDT Demo - Figures! " #$#%& " 14

15 Webservices Invocation Framework Middleware component Simple Java API for invoking webservices, no matter how or where they are provided Released to Apache But IBM wants a version tightly coupled to IBMs normal qualities of service IBM tracing/monitoring/management How do we manage this? Manage an IBM internal of the apache codebase? Put the IBM facilities into the open source codebase? 15

16 AJDT Demo - WSIF ' ()! " #$#%& " 16

17 Demo conclusions Capabilities of AOP technology look very promising Code size reduction No tangling Faster development times Product-line engineering 17

18 Eliminating tangling BEFORE! "# $$%&## '(# ('()*+('!!, --.. %-- /0-- %-- /- -#0! &&- && '(#( ( AFTER! "#!, -- /- -#0! Crosscutting concerns extracted 18 Example: Code to handle EJB Entity bean passivation

19 Adopting AOP reward 19 time & confidence

20 Adopting AOP reward Risky Space 20 time & confidence

21 Adopting AOP reward exploration/ enforcement auxiliary / infrastructure core / business AO Analysis, AO Design, AO Strategy 21 time & confidence

22 Exploration & Enforcement Aspects to monitor, analyze, debug system Can use individually or share with team Aspects that ensure design integrity Can run privately, as part of nightly build, or shared w/ team Sharing with team can be supported by integration in IDE or including in ant script No runtime dependency on AspectJ production code has not been touched by AspectJ 22

23 Don t use System.err.println!!! Warn developers using System.out, System.err and printstacktrace #0-# &&& #0 # 1,! #-2 2..,! %-0&& #0 #& 1 & & !,-5#64 -,&1 #.. #& 1 78#'0!-&&7 23

24 Architectural Layering Persistence Layer 4 Model Layer 3 View Layer 2 24 Controller Layer 1

25 Map packages to components # 9!0 #0 :, 1,!,2 #0 ;- 1,! -2 #0 %-- 1,! --2 #0 1,! #2 < 25

26 External calls into components < #0,% ,2..:, #0 -% ;- #0 --% %-- #0 #% #2.. #0% =- =-2 2 < 26

27 Compile warnings for illegal calls < -,&1 1--%-- 1 7> ,&1 1,%--..% , -----,7 -,&1 1-%--.. %-- 33:, 1 7-, , ,&1 1#%--..; #- --#-7 -,& 1% !--- -!

28 Auxiliary/Infrastructure Whole team awareness developers know aspects are there runtime dependency on aspectjrt.jar But only some developers change working practices change day-to-day tools Easily understood business case 28

29 Examples 29 Tracing, logging Error and exception handling Monitoring and statistics gathering Transactions Session management (for e.g. persistence) Threading Synchronization Caching Remote access

30 Building the Case Factors: Number of source files in project Average time spent per file over a release (e.g. on tracing code)?@@-?a0/)a#!0 A@@-?A0/*A#,6?@@@-?A0/+#,6 30

31 Building the Case You can certainly write and test a simple tracing aspect in < 25 hours write and test a good tracing aspect in < 50 hours and save a lot of time?@@-?a0/)a#!0 A@@-?A0/*A#,6?@@@-?A0/+#,6 31

32 Core/Business Aspects Using aspects when implementing application s core functionality (e.g. security) Requires full team buy-in to AspectJ Changes to tool set (e.g. JDT -> AJDT) You ll be ready if you followed staged approach enough developers will understand technology enough developers will be aware of value management will be aware of value 32

33 CapitalOne BEA icecentric (icecentric.com) - CRM company Virtusa Virtusa.com (a global provider of software development services) fcspartners.fi Siruis Software Cardinal Health, Dublin, OH BerMark Dynamics Inc. Tavant Technologies Asset Group, part of SAIC - fortune 500. asset.com Haywood Associates SpinSoftware The Middleware Company atsistemas (atsistemas.com) Wells Fargo IntelliJ Bell Canada (sympatico.ca) Dimension Data Husky Injection Molding Systems husky.ca Covansys Global Technology Services covansys.com OleCenter Addecco Group olecenter.com Bell South (.net) EDS Simtel Group Simtel.ie HP Data Transfer datatransfer.com.ar matrix-media.com MetCash (marketing an distribution) metcash.com SG Corporate & Investmen Banking (sgcib.com Intuit intuit.com Disney disney.com CrimsonLogic crimsonlogic.com Reflective Solutions reflective.com (J2EE consultancy) New Aspects of Software etracksolutions.com Nulogy Corporation nulogy.com SAS sas.com VMS vmsinfo.com Deloitte dc.com Global Net Services gnsi.com A G Edwards (finance company) AGEDWARDS.com Akzo Nobel (pharmaceuticals) AkzoNobel.com Perot Systems (trcinc.com) Siemens ESRI (GPS and mapping software specialists) esri.com Computer Sciences Corporation csc.com 33 Oracle ARINC "the world leader in transportation communications and systems engineering" Arinc.com MAN-Corporate hpsglobal.com CheckFree Allstate Insurance *posters to AspectJ user mailing list, Jan-May 2004, where affiliation can be determined.

34 Summary Object Oriented Development has some shortcomings for coping with certain kinds of feature/concern AOP can help solve this problem You need tools support Adopt AOP through managed phases Get increasing benefit as your confidence and expertise grows Who s doing it? IBM is doing it Other AspectJ users are doing it You can do it too! 34

35 Beyond Java Obviously there are languages other than Java BPEL, WSDL, C, C++, etc, etc there are artifacts other than code Documentation, build scripts, UML models IBM is exploring this space check out the CME project 35

36 More information AspectJ homepage AJDT homepage Books AspectJ in Action ISBN Eclipse AspectJ ISBN Contact me! Andy Clement 36

37 The End 37