Aspect Oriented Programming (Droidcon Paris 2015 BarCamp)

Add magic to your code and remove boilerplate

Transcript

1. Aspect Oriented
   Programming
   Add magic to your code and remove boilerplate
   Droidcon Paris 2015 Barcamp
   

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2. About...
   Xavier Gouchet
   Android software engineer
   (Tools, architecture, core, …)
   @xgouchet on Github, StackOverflow, Twitter, …
   speakerdeck.com/xgouchet
   

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3. 1.
   Introduction
   What is it ? What is it not ?
   

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4. It’s NOT ...
   ◎ A new programming language
   ◎ Something to replace OOP
   ◎ The solution to all your problems !
   

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5. It is a tool to ...
   ◎ Enhance modularity
   ◎ Separate cross cutting concerns
   ◎ Focus on business logic
   ◎ Reduce noise in the source code
   

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6. 2.
   Aspects Oriented
   Programming
   The general idea
   

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7. void foo() {
   Log.v("Tag", "foo");
   beginTransaction();
   try {
   bar();
   // ...
   setTransactionSuccessful();
   } catch (Exception e) {
   reportError(e);
   } finally {
   endTransaction();
   }
   Log.v("Tag", "foo done");
   }
   Before / After
   

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8. void foo() {
   Log.v("Tag", "foo");
   beginTransaction();
   try {
   bar();
   // ...
   setTransactionSuccessful();
   } catch (Exception e) {
   reportError(e);
   } finally {
   endTransaction();
   }
   Log.v("Tag", "foo done");
   }
   Before / After
   

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9. void foo() {
   Log.v("Tag", "foo");
   beginTransaction();
   try {
   bar();
   // ...
   setTransactionSuccessful();
   } catch (Exception e) {
   reportError(e);
   } finally {
   endTransaction();
   }
   Log.v("Tag", "foo done");
   }
   Before / After
   

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10. void foo() {
    Log.v("Tag", "foo");
    beginTransaction();
    try {
    bar();
    // ...
    setTransactionSuccessful();
    } catch (Exception e) {
    reportError(e);
    } finally {
    endTransaction();
    }
    Log.v("Tag", "foo done");
    }
    Before / After
    

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11. void foo() {
    Log.v("Tag", "foo");
    beginTransaction();
    try {
    bar();
    // ...
    setTransactionSuccessful();
    } catch (Exception e) {
    reportError(e);
    } finally {
    endTransaction();
    }
    Log.v("Tag", "foo done");
    }
    Before / After
    

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12. void foo() {
    Log.v("Tag", "foo");
    beginTransaction();
    try {
    bar();
    // ...
    setTransactionSuccessful();
    } catch (Exception e) {
    reportError(e);
    } finally {
    endTransaction();
    }
    Log.v("Tag", "foo done");
    }
    Before / After
    

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13. @LogMethod
    @SafeTransaction
    void foo() {
    bar();
    // ...
    }
    Before / After
    

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14. Cross-cutting
    concerns
    Logging, performances,
    security, transaction,
    validation, serialization,
    cache, notification,
    multithreading, ...
    

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15. .class ul { display: inline;}
    #id p {font-style: italic;}
    a:hover {color: #FF4630; }
    input[type=text] {font-family: monospace;}
    CSS + HTML
    

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16. .class ul { display: inline;}
    #id p {font-style: italic;}
    a:hover {color: #FF4630; }
    input[type=text] {font-family: monospace;}
    CSS + HTML
    Attributes
    behaviors/appearance applied to...
    
    markup nodes in the source code,
    defined by...
    Selectors
    rules and patterns
    

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17. Vocabulary
    Advices
    behaviors applied to...
    JoinPoints
    positions in the source code,
    defined by...
    PointCuts
    rules and patterns
    Attributes
    behaviors/appearance applied to...
    
    markup nodes in the source code,
    defined by...
    Selectors
    rules and patterns
    

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18. 4.
    Hello AOP
    Let’s write an aspect
    

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19. Bytecode
    weaving
    AspectJ
    

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20. 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) {
    Log.v("AspectTag", "> " + jp.getSignature());
    }
    }
    

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21. 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) {
    Log.v("AspectTag", "> " + jp.getSignature());
    }
    }
    

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22. 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) {
    Log.v("AspectTag", "> " + jp.getSignature());
    }
    }
    

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23. 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) {
    Log.v("AspectTag", "> " + jp.getSignature());
    }
    }
    

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24. 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) {
    Log.v("AspectTag", "> " + jp.getSignature());
    }
    }
    

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25. 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) {
    Log.v("AspectTag", "> " + jp.getSignature());
    }
    }
    

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26. 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) {
    Log.v("AspectTag", "> " + jp.getSignature());
    }
    }
    

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27. 5.
    Concrete examples
    Beyond the logging “Hello world”
    

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28. Performance Monitoring
    @Aspect
    public class PerformanceMonitorAspect {
    @Pointcut("execution(@Monitor * *(..))")
    public void monitoredMethod(){}
    @Around("monitoredMethod())")
    public Object advice(ProceedingJoinPoint pjp) {
    long start = System.nanoTime();
    Object result = pjp.proceed();
    long end = System.nanoTime();
    Log.i("Monitored", jp.toString + " : "
    + (end - start) + "ns");
    return result;
    }
    }
    

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29. Performance Monitoring
    @Aspect
    public class PerformanceMonitorAspect {
    @Pointcut("execution(@Monitor * *(..))")
    public void monitoredMethod(){}
    @Around("monitoredMethod())")
    public Object advice(ProceedingJoinPoint pjp) {
    long start = System.nanoTime();
    Object result = pjp.proceed();
    long end = System.nanoTime();
    Log.i("Monitored", jp.toString + " : "
    + (end - start) + "ns");
    return result;
    }
    }
    

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30. Performance Monitoring
    @Aspect
    public class PerformanceMonitorAspect {
    @Pointcut("execution(@Monitor * *(..))")
    public void monitoredMethod(){}
    @Around("monitoredMethod())")
    public Object advice(ProceedingJoinPoint pjp) {
    long start = System.nanoTime();
    Object result = pjp.proceed();
    long end = System.nanoTime();
    Log.i("Monitored", jp.toString + " : "
    + (end - start) + "ns");
    return result;
    }
    }
    

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31. Memoization
    @Aspect
    public class MemoizationAspect {
    @Pointcut("execution(@Memoize * *(..))")
    public void memoizedMethod() {}
    @Around("memoizedMethod()")
    public Object advice(ProceedingJoinPoint pjp) {
    Object cached = getCached(pjp);
    if (cached == null) {
    cached = pjp.proceed();
    cacheResult(pjp, cached);
    }
    return cached;
    }
    }
    

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32. Database Transaction
    @Aspect
    public class SQLiteTransactionAspect {
    @Pointcut("execution(@SQLiteTransaction * *(..))")
    public void transactionMethod(){}
    @Around("transactionMethod() && args(db)")
    public void advice(ProceedingJoinPoint jp,
    SQLiteDatabase db) {
    db.beginTransaction();
    try {
    jp.proceed();
    db.setTransactionSuccessful();
    } catch (SQLiteException e) {
    Log.e("SQLite", "Error at" + jp.toString(), e);
    } finally {
    db.endTransaction();
    }
    }
    }
    

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33. Database Transaction
    @Aspect
    public class SQLiteTransactionAspect {
    @Pointcut("execution(@SQLiteTransaction * *(..))")
    public void transactionMethod(){}
    @Around("transactionMethod() && args(db)")
    public void advice(ProceedingJoinPoint jp,
    SQLiteDatabase db) {
    db.beginTransaction();
    try {
    jp.proceed();
    db.setTransactionSuccessful();
    } catch (SQLiteException e) {
    Log.e("SQLite", "Error at" + jp.toString(), e);
    } finally {
    db.endTransaction();
    }
    }
    }
    

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34. Database Transaction
    @Aspect
    public class SQLiteTransactionAspect {
    @Pointcut("execution(@SQLiteTransaction * *(..))")
    public void transactionMethod(){}
    @Around("transactionMethod() && args(db)")
    public void advice(ProceedingJoinPoint jp,
    SQLiteDatabase db) {
    db.beginTransaction();
    try {
    jp.proceed();
    db.setTransactionSuccessful();
    } catch (SQLiteException e) {
    Log.e("SQLite", "Error at" + jp.toString(), e);
    } finally {
    db.endTransaction();
    }
    }
    }
    

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35. Validation
    @interface Validation { String regexp() default ".*";
    }
    public class UserAccount {
    @Validation(regexp = "[a-zA-Z]{6,}")
    public void setUserName(String userName) {
    mUserName = userName;
    }
    @Validation(regexp = "^(?=.*\d)(?=.*[A-Z]).{8,}$")
    public void setPassword(String password) {
    mPassword = password;
    }
    }
    

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36. Validation
    @interface Validation { String regexp() default ".*";
    }
    public class UserAccount {
    @Validation(regexp = "[a-zA-Z]{6,}")
    public void setUserName(String userName) {
    mUserName = userName;
    }
    @Validation(regexp = "^(?=.*\d)(?=.*[A-Z]).{8,}$")
    public void setPassword(String password) {
    mPassword = password;
    }
    }
    

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37. Validation
    @Aspect
    public class ValidationAspect {
    @Before("execution(@Validation * *(..))
    && args(input) && @annotation(v)")
    public void advice(JoinPoint jp,
    String input,
    Validation v) {
    Pattern pattern = Pattern.compile(v.regexp());
    Matcher matcher = pattern.matcher(input);
    if (!matcher.matches()) {
    throw new InvalidInputException();
    }
    }
    }
    

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38. Validation
    @Aspect
    public class ValidationAspect {
    @Before("execution(@Validation * *(..))
    && args(input) && @annotation(v)")
    public void advice(JoinPoint jp,
    String input,
    Validation v) {
    Pattern pattern = Pattern.compile(v.regexp());
    Matcher matcher = pattern.matcher(input);
    if (!matcher.matches()) {
    throw new InvalidInputException();
    }
    }
    }
    

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39. Validation
    @Aspect
    public class ValidationAspect {
    @Before("execution(@Validation * *(..))
    && args(input) && @annotation(v)")
    public void advice(JoinPoint jp,
    String input,
    Validation v) {
    Pattern pattern = Pattern.compile(v.regexp());
    Matcher matcher = pattern.matcher(input);
    if (!matcher.matches()) {
    throw new InvalidInputException();
    }
    }
    }
    

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40. What about the stack trace ?
    com.example.InvalidInputException
    at com.example.ValidationAspect.advice(ValidationAspect.java:35)
    at com.example.MyClass.setPassword(UserAccount.java:83)
    at com.example.test.UserAccount.onSubmit(UserAccount.java:42)
    ... 5 more
    

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41. Undo / Redo
    interface IUndoableAction {
    public void undo();
    public void redo();
    }
    class FieldAction implements IUndeoableAction {
    Field mField; Object mTarget, mOldValue, mNewValue;
    public FieldAction(Object target, Field field,
    Object oldValue, Object newValue) {
    mField = field;
    mTarget = target;
    mOldValue = oldValue;
    mNewValue = newValue;
    }
    public void undo(){ field.set(target, oldValue); }
    public void redo(){ field.set(target, newValue); }
    }
    

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42. Undo / Redo
    @Aspect
    public class UndoActionAspect {
    @Pointcut("within(com.example.model.*)")
    public void withinModelClass() {}
    @Before("withinModelClass() && set(public * *)
    && args(newValue) && target(target)")
    public void advice(JoinPoint jp,
    Object target,
    Object newValue) {
    Field field = getField(jp, target);
    Object oldValue = field.get(target);
    UndoManager.getInstance()
    .record(new FieldAction(target, field,
    oldValue, newValue);
    }
    }
    

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43. Gatekeeping
    enum Role { DEV, BETA, PUBLIC }
    @interface GateKeep { Role[] allowed(); }
    public class HomeActivity {
    @GateKeep(allowed = {DEV, BETA})
    public void setupMaterialUI() {
    // ...
    }
    @GateKeep(allowed = {DEV})
    public void startJukeboxPlayer() {
    // ...
    }
    }
    

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44. Gatekeeping
    @Aspect
    public class GateKeepAspect {
    @Around("execution(@GateKeep * *(..)) &&
    @annotation(gk)")
    public void advice(ProceedingJoinPoint jp,
    Gatekeep gk) {
    Role userRole = UserService.getInstance()
    .getCurrentUser()
    .getRole();
    if (Arrays.asList(gate.allowedRoles())
    .contains(userRole)) {
    jp.proceed();
    }
    }
    }
    

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45. Multithreading
    @Aspect
    public class UIThreadAspect {
    final Handler mMainHandler =
    new Handler(Looper.
    getMainLooper());
    @Around("execution(@RunOnUIThread void *(..))")
    public void advice(final ProceedingJoinPoint jp) {
    if (Looper.myLooper() == Looper.getMainLooper())
    {
    jp.proceed();
    } else {
    mMainHandler.post(new Runnable() {
    public void run() {
    jp.proceed();
    }
    });
    }
    }
    

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46. and more...
    Retry failed request
    Read/write locks
    Boilerplate code
    

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47. 6.
    More than just
    advices
    

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48. @Aspect
    @DeclarePrecedence("around1, before2, after3,
    around4, before5, after6")
    public class OrderingAspect {
    // Applied to the same pointcut, the result will be
    // around1 {
    // before2
    // around4 {
    // before5
    // joinpoint
    // after3
    // }
    // }
    // after4
    }
    Ordering advices
    

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49. 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 SEP_OF_CONCERNS =
    "Core classes should not call UI methods";
    }
    

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50. Mixins
    interface INamed {
    String getName();
    }
    class NamedImpl implements INamed {
    private String mName;
    public NamedImpl(Object namedObject) {
    mName = namedObject.toString();
    }
    public String getName() {
    return mName;
    }
    }
    

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51. Mixins
    @Aspect
    public class NamedAspect {
    @DeclareMixin("com.example..*")
    public static INamed makeNamed(Object namedObject)
    {
    return new NamedImpl(namedObject);
    }
    }
    class Foo {
    public void hello (){
    Log.i("Hello", "My name is "
    + ((INamed) this).getName());
    }
    }
    

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52. 5.
    General advices
    no pun intended...
    

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53. “
    ♬
    “Forever in debt
    to your priceless advice”
    Nirvana
    

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54. Things to remember
    ◎ Singleton by default
    ◎ Inheritance, abstracts, generics,
    inner classes…
    ◎ Android flavors
    ◎ AOP is real programming
    

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55. “
    “It’s a kind of magic”
    Queen
    ♬
    

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56. Wizardry or Witchcraft
    @Aspect
    public class PreventNPEAspect {
    @Pointcut("within(com.example.model.*)")
    public void withinModelClass() {}
    @Around("withinModelClass() && execution(* *(..))")
    public void advice(ProceeJoinPoint jp) {
    Object[] args = jp.getArgs();
    for (int i = 0; i < args.length; i++) {
    if (args[i] == null) {
    args[i] = "";
    }
    }
    jp.proceed(args);
    }
    }
    

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57. Wizardry or Witchcraft
    @Aspect
    public class PreventNPEAspect {
    @Around("execution(@PreventStringNPE * *(..))")
    public void advice(ProceeJoinPoint jp) {
    Object[] args = jp.getArgs();
    for (int i = 0; i < args.length; i++) {
    if (args[i] == null) {
    args[i] = "";
    }
    }
    jp.proceed(args);
    }
    }
    

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58. Errors to avoid
    ◎ Pokeball : gotta catch’em all
    Pointcuts must be as precise as possible
    ◎ Octopuss : arms reaching everywher
    Pointcuts matching unrelated joinpoints
    ◎ Asp’ception : because aspect is code too
    Pointcuts matching the advice itself
    ◎ Aspector Gadget : single responsibility
    SOLID principles apply to AOP as well
    

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59. Thanks ! Any question ?
    We’re hiring
    deezer.com/jobs
    speakerdeck.com/xgouchet
    

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60. A.
    Addendum
    Gradle script
    

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61. The easy way
    buildscript {
    dependencies {
    classpath 'com.uphyca.gradle:gradle-android-aspectj-plugin:
    0.9.14'
    }
    }
    apply plugin: 'com.uphyca.android-aspectj'
    dependencies {
    compile 'org.aspectj:aspectjrt:1.8.1'
    }
    

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