Aspect Oriented Programming (Internal Brown Bag Lunch 2015)

An introduction to the concepts of AOP, with Java examples.
Internal presentation at Deezer's Brown Bag Lunch

Transcript

1. Aspect Oriented Programming Aspect Weaving / Code Weaving
2. A new programming language Something to replace OOP The solution to all your problems It’s not...
3. Enhance modularity Separate cross cutting concerns Separate business logic from tech code Reduce noise in the source code What is it ?
4. Before Example After void doSomething() { log(“doSomething”); beginTransaction(); try { callMethod(); ... setTransactionSuccessful(); } catch (e) { reportError(e); } finally { endTransaction(); } log(“done”); } @SafeTransaction void doSomething() { callMethod(); ... }
5. Cross cutting concerns Logging, Performance, Security, Transaction, Validation, Serialization, Cache, Notification, MultiThreading, ...
6. Vocabulary Advice (behavior) applied to JoinPoints (position in the source code) based on PointCut (rules / pattern)
7. Attributs (visual aspects) applied to <Elements/> (markup nodes in source code) based on Selectors (rules / pattern) Widely used on the web since 1996
8. Code Weaving Inject code at compile time No noticeable impact on performance
9. Code weaving
10. Hello World @interface TraceLog{} public class MyClass { @TraceLog public void foo() { // … } } @Aspect public class TraceLogAspect { @Pointcut(“execution(@TraceLog * *(..))”) public void traceLogMethod(){} @Before(“traceLogMethod()”) public void advice(JoinPoint jp) { Logger.log(“> ” + jp.getSignature()); } }
11. @Aspect public class PerformanceMonitorAspect { @Pointcut(“execution(@Monitor * *(..))”) public void monitoredMethod(){} @Around(“monitoredMethod()”) public void advice(ProceedingJoinPoint jp) { long start = getCurrentTime(); jp.proceed(); long end = getCurrentTime(); // ... } } @interface Monitor{} public class MyClass { @Monitor public void foo() { // … } } Performance
12. @Aspect public class DBTransactionAspect { @Around(“execution(@Transaction * *(..)) && args(db, ..)”) public void advice(ProceedingJoinPoint jp, SQLiteDatabase db) { db.beginTransaction(); try { jp.proceed(); db.setTransactionSuccessful(); } catch (SQLiteException e) { // ... } finally { db.endTransaction(); } } } Transactions
13. Validation @interface Validate{ String regexp() default “.*”; } public class MyClass { @Validate(regexp=“[a-zA-Z0-9_-]{3-15}”) public void setUserName(String userName) { // … } @Validate(regexp=“((?=.*\\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%]).{6,20})”) public void setPassword(String password) { // … } @Validate(regexp=“[A-Z0-9._%+-]+@[A-Z0-9.-]+\\.[A-Z]{2,4}”) public void setEmail(String userName) { // … } }
14. @Aspect public class InputValidationAspect { @Before(“execution(@Validate * *(..)) && args(input, ..)”) public void advice(JoinPoint jp, String input) { Validate v = jp.getSignature() .getMethod() .getAnnotation(Validate.class); Pattern pattern = Pattern.compile(v.regexp()); Matcher matcher = pattern.matcher(input); if (!matcher.matches()) { throw new InvalidInputException(); } } } Validation
15. Undo / Redo interface IUndoableAction { public void undo(); public void redo(); } class UndoManager { public void record(IUndoableAction action) { // ... } }
16. Undo / Redo class UndoableFieldAction { Field field; Object target, oldValue, newValue; public UndoableFieldAction(Object t, Field f, Object ov, Object nv) { field = f; target = t; oldValue = ov; newValue = nv; } public void undo(){ field.set(target, oldValue); } public void redo(){ field.set(target, newValue); } }
17. Undo / Redo @Aspect public class UndoActionAspect { @Pointcut(“within(com.example.model.*)”) public void withinModelClass() {} @Pointcut(“set(public * *)”) public void setPublicField() {} @Before(“withinModelClass() && setPublicField() && args(val) && target(obj)”) public void advice(JoinPoint jp, Object obj, Object val) { Field field = getField(jp, obj); Object oldValue = field.get(obj); UndoManager.getInstance() .record(new UndoableFieldAction(obj, field, oldValue, val); } }
18. Security / Gatekeeping enum Role { ADMIN, USER, ANONYMOUS } @interface GateKeep { Role[] allowed(); } @GateKeep(allowed = {ADMIN, USER}) public void foo() { // ... }
19. @Aspect public class SecurityAspect { @Around(“execution(@GateKeep * *(..))”) public void advice(ProceedingJoinPoint jp) { GateKeep gate = jp.getSignature() .getMethod() .getAnnotation(GateKeep.class); Role userRole = UserService.getInstance() .getCurrentUser() .getRole(); if (Arrays.asList(gate.allowedRoles()).contains(userRole)) { jp.proceed(); } } } Security / Gatekeeping
20. MultiThreading @Aspect public class UIThreadAspect { @Around(“execution(@UIThread * *(..))”) public void advice(final ProceedingJoinPoint jp) { Runnable task = new Runnable() { public void run() { jp.proceed(); } }; new Handler(Looper.getMainLooper()).post(task); } }
21. Compile Time Checks @Aspect public class CoreCheckAspect { @Pointcut(“within(com.example.core.*)”) public void withinCorePackage() {} @Pointcut(“call(* com.example.ui..*..*(..))”) public void callToUIMethod() {} @DeclareError(“withinCorePackage() && callToUIMethod()”) static final String MESSAGE = “Core classes should not call UI methods”; }
22. A kind of magic... “With great power come great responsibilities”
23. The “Pokeball” Pointcut (Gotta catch’em all) The “Octopuss” Pointcut Asp’ception (Because advice can be caught by pointcut too) The Aspector Gadget (An aspect with more advices than you can count) Errors to avoid
24. AspectJ Java PostSharp C# AspectC++ C++ Aspects ObjC Go! AOP PHP php Aspector Ruby Libraries
25. Any question ? Thanks for your attention