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Aspect Oriented Programming (Droidcon Paris 2015 BarCamp)

Aspect Oriented Programming (Droidcon Paris 2015 BarCamp)

Add magic to your code and remove boilerplate

Xavier Gouchet

November 09, 2015
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  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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