面向方面的编程.ppt

1、2020/8/14,Institute of Computer Software Nanjing University,1,Aspect Oriented Programming,面向方面的编程,2020/8/14,Institute of Computer Software Nanjing University,2,摘要,Background and Motivation AOP AspectJ Summary,2020/8/14,Institute of Computer Software Nanjing University,3,摘要,Background and Motivation

2、AOP AspectJ Summary,2020/8/14,Institute of Computer Software Nanjing University,4,Background and Motivation,Where OOP has brought us Reusability of components Modularity Less complex implementation Reduced cost of maintenance Modularity is a universal advancement over structured programming that lea

3、ds to clearer and better understood software,2020/8/14,Institute of Computer Software Nanjing University,5,Modularity in Reality,Code from org.apache.tomcat,XML Parsing,Red shows relevant lines of code,Nicely fits in one box,Good Modularity,2020/8/14,Institute of Computer Software Nanjing University

4、,6,Modularity in Reality,URL pattern matching,Pretty Good Modularity,fits in two boxes,2020/8/14,Institute of Computer Software Nanjing University,7,Modularity in Reality,Logging,Red shows lines of code that handle logging,Not in just one place,Not even in a small number of places,Bad Modularity,Cod

5、e tangling and scattering,2020/8/14,Institute of Computer Software Nanjing University,8,History of Programming Paradigms,In the beginning: Programming in whichever way. Monolithic programs,2020/8/14,Institute of Computer Software Nanjing University,9,History of Programming Paradigms,Structured Progr

6、amming Functional decomposition,Modularity,2020/8/14,Institute of Computer Software Nanjing University,10,History of Programming Paradigms,Object-Oriented Programming Encapsulation this.x =x; this.y=y; TraceSupport.traceExit(“Point.set”); ,A motivating example: Tracing,2020/8/14,Institute of Compute

7、r Software Nanjing University,14,Java API Example,package java.io; public class File implements java.io.Serializable private String path; public boolean exists() SecurityManager security = System.getSecurityManager(); if(security!=null) security.checkRead(path); return exits0(); public boolean canRe

8、ad() SecurityManager security = System.getSecurityManager(); if(security!=null) security.checkRead(path); return canRead0(); ,Same code repeated 16 times in java.io.File,2020/8/14,Institute of Computer Software Nanjing University,15,Crossing cutting concerns,2020/8/14,Institute of Computer Software

9、Nanjing University,16,What is a concern?,A particular goal, concept, or area of interest (requirement) A software system contains: Business (application) logic concerns System-level concerns,2020/8/14,Institute of Computer Software Nanjing University,17,Crosscutting Concerns,Crosscutting is how to c

10、haracterize a concern than spans multiple units of OO modularity Crosscutting concerns resist modularization using normal OO construct,2020/8/14,Institute of Computer Software Nanjing University,18,Separation of Concerns (SoC),Object-Oriented Programming separates and encapsulates some concerns Othe

11、rs end up tangled and scattered Basic problem N dimensions of concerns 1 dimension of implementation structure Tyranny decomposition,2020/8/14,Institute of Computer Software Nanjing University,19,Approaches to SoC,Composition Filters Multi-dimensional Separation of Concerns Adaptive Programming Aspe

12、ct-Oriented Programming Was developed at Xerox PARC （施乐公司 帕洛阿尔托研究中心） (Related) Meta-Object Protocol (MOP) Reflective programming, meta-object protocol,2020/8/14,Institute of Computer Software Nanjing University,20,摘要,Background and Motivation AOP AspectJ Summary,2020/8/14,Institute of Computer Softw

13、are Nanjing University,21,The AOP Idea,Many cross-cuts arent random! They serve specific purposes They have well-defined structure Solets capture the cross-cutting structure in a modular way to better support for “Separation of Concerns”,2020/8/14,Institute of Computer Software Nanjing University,22

14、,Two central problems AOP tries to solve,Code tangling One module, many concerns,Code scattering One concern, many modules,Example: logging,2020/8/14,Institute of Computer Software Nanjing University,23,Two central problems AOP tries to solve,2020/8/14,Institute of Computer Software Nanjing Universi

15、ty,24,AOP approach to SoC,2020/8/14,Institute of Computer Software Nanjing University,25,Prism Analogy,Crosscutting concerns,Implement each concern separately,Weave concerns together,2020/8/14,Institute of Computer Software Nanjing University,26,Basic Mechanisms of AOP,Aspect,Pointcut,Advice,Weaving

16、,2020/8/14,Institute of Computer Software Nanjing University,27,Summary so far,AOP is a software development technique that complements and extends OOP Provides new and powerful ways to modularize “crosscutting concerns” Crosscutting concerns: Behavior that cuts across class boundaries AspectJ is th

17、e leading implementation of AOP that extends Javas OOP model,2020/8/14,Institute of Computer Software Nanjing University,28,摘要,Background and Motivation AOP AspectJ Summary,2020/8/14,Institute of Computer Software Nanjing University,29,What is AspectJ?,A simple and practical aspect-oriented extensio

18、n to Java A general purpose AO language Based on over ten years of research at Xerox PARC Launched in 1998 Transferred to E in 2002 /aspectj/ Latest version: AspectJ 1.6.2,2020/8/14,Institute of Computer Software Nanjing University,30,Design assumptions,Real Community

19、Users Writing aspects Reading aspects Idioms How effective for concerns Modular, reusable and easy to develop and maintain Java compatibility Upward compatibility Platform compatibility Tool compatibility Programmer Compatibility,2020/8/14,Institute of Computer Software Nanjing University,31,AspectJ

20、 Compilation Process,weaving,Application System,ajc: javac extension,2020/8/14,Institute of Computer Software Nanjing University,32,Dynamic VS Static crosscutting,Dynamic crosscutting define additional behavior to run at certain well-defined points in the execution of the program Static crosscutting

21、 modify the static structure of a program (e.g., adding new methods, implementing new interfaces, modifying the class hierarchy),2020/8/14,Institute of Computer Software Nanjing University,33,Concepts in AspectJ,Join Points 连接点 Pointcut 切入点 Advice 通知 Aspect 方面 Introduce 引入,2020/8/14,Institute of Com

22、puter Software Nanjing University,34,High level View of AspectJ,Java Program,AspectJ,Advice,pointcut,advice body,join point,2020/8/14,Institute of Computer Software Nanjing University,35,Join Points Model,Join point is a well-defined point in a programs execution Method call:,Public void move(int dx

23、, int dy) setX(_x+dx); setY(_y+dy); ,Method call join point,2020/8/14,Institute of Computer Software Nanjing University,36,More Join Points,public void setX(int x) _x = x; ,Method execution join point,Field set join point,2020/8/14,Institute of Computer Software Nanjing University,37,All Join Points

24、,method ,2020/8/14,Institute of Computer Software Nanjing University,39,Named Pointcuts,Can be a Named set of join points Capture all the executions of the or method,pointcut move(): execution (void Point.setX(int) | execution (void Point.setY(int);,Name and parameters,Executions of methods with the

25、 specified sig.,or,2020/8/14,Institute of Computer Software Nanjing University,40,More on Pointcuts,Basic pointcuts and pointcuts composition Pointcuts can be composed as boolean expressions with “ after() returning: move() /code here runs after each move ,Example:,2020/8/14,Institute of Computer So

26、ftware Nanjing University,45,Aspects,Mix everything weve seen up to now and put it one or more modular units called Aspects. Looks a lot like a class! Can contain pointcuts, advice declarations, methods, variables .,2020/8/14,Institute of Computer Software Nanjing University,46,How it works,Short an

27、swer: bytecode modification,2020/8/14,Institute of Computer Software Nanjing University,47,A first example,2020/8/14,Institute of Computer Software Nanjing University,48,What it does,Sample Code,2020/8/14,Institute of Computer Software Nanjing University,49,An example from Xeroxs AspectJ Tutorial,So

28、urce ,Sample Code,2020/8/14,Institute of Computer Software Nanjing University,50,AspectJs Introductions,An introduction is an aspect member that allows to Add methods to an existing class Add field to an existing class Extend an existing class with another Implement an interface in an existing class

29、 Convert checked exceptions into unchecked exceptions,2020/8/14,Institute of Computer Software Nanjing University,51,Introduction examples,public int foo.bar(int x); private int foo.counter; declare parents: mammal extends animal; declare parents: MyThread implements MyThreadInterface;,2020/8/14,Ins

30、titute of Computer Software Nanjing University,52,Some Advanced Topics,Aspect Extension (Inheritance) example,2020/8/14,Institute of Computer Software Nanjing University,53,Some Advanced Topics,Aspect Creation (Association) Aspect instance Single (static) vs. Multiple (dynamic) Default: Singleton, c

31、reated when program begins Object (Class) association: perthis, pertarget Controlflow association Percflow, percflowbelow Aspect & Advice Precedence & Interactions,2020/8/14,Institute of Computer Software Nanjing University,54,Performance impact,See “Advice Weaving in AspectJ” “The implementation of

32、 advice weaving introduces very little performance overhead when compared to the same functionality coded by hand.” Does make it easy to create performance destroying code But allows powerful optimizations,2020/8/14,Institute of Computer Software Nanjing University,55,AspectJ Terminology,a join poin

33、t is a well-defined point in the program flow a pointcut is a group of join points advice is code that is executed at a pointcut introduction modifies the members of a class and the relationships between classes a compile time declaration introduces a compile time warning or error upon detection of

34、certain usage patterns an aspect is a module for handling crosscutting concerns Aspects are defined in terms of pointcuts, advice, and introduction Aspects are reusable and inheritable,2020/8/14,Institute of Computer Software Nanjing University,56,Dynamic AOP Systems,Creating aspects at run-time Spe

35、cifying pointcuts at run-time Dynamic code translation (or some special feature of the run-time environment) Enabling/disabling aspects at run-time Pointcuts are dynamic: it can be decided only at run-time whether advices have to be executed or not (based on run-time values, call-stack, etc.),2020/8

36、/14,Institute of Computer Software Nanjing University,57,Other Java AOP sightings,AspectWerkz: load-time/run-time weaving, AOP constructs defined using javadoctags BEA: AOP framework for Weblogic JBoss AOP framework AOP with interceptors Spring framework Limited AOP with proxies J2EE without EJB Asp

37、ectJ2EE JasCo ,2020/8/14,Institute of Computer Software Nanjing University,58,Other Aspect-Oriented Languages,AspectC AspectC+ Aspect.Net Lightweight Python AOP AspectL(Lisp) AspectML AspectPHP,2020/8/14,Institute of Computer Software Nanjing University,59,Middleware & System Level Applications,Security Transaction Persistence Mobility Realtime& Embedded Systems OS ,2020/8/14,Institute of Computer Software Nan