J2ObjC. Cross platform development - Google way

The presentation was given at: https://devfest.gdg.org.ua

The war between mobile platforms is over. After several years of active competition, we’ve got two operating systems with almost the same quality and feature set.

For mobile developers this means that all further projects should target at least two platforms. In this talk, Vitaliy wants to share results of internal R&D experiments at GetSocial with J2ObjC – Java to Objective-C translation tool developed by Google.

J2ObjC goal is to write an app’s non-UI code (such as application logic and data models) in Java, which is then shared with no editing by Android and iOS apps.

Transcript

1. Cross platform development - Google way
   J2ObjC
   Vitaliy Zasadnyy
   Head of Mobile @ GetSocial
   

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2. In yellow boxes like this one you can find comments to
   the slide.
   Enjoy the presentation and if you have any questions,
   feel free to reach me at v@zasadnyy.com
   

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3. #dfua
   hard
   Cross platform development is
   

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4. #dfua
   70%
   code reuse
   Source: Gmail Blog
   

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5. #dfua
   25+ projects
   Google is using J2ObjC for almost all office apps.
   Besides Google, more than 25 projects claimed using
   J2ObjC.
   

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6. Now I’m leading mobile department at Dutch startup
   GetSocial
   

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7. With help of GetSocial SDK you can add Activity Feed,
   Chat, Notifications or Smart Invites just with a few lines
   of code
   

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8. SDK is available for Android, iOS, Unity and Cordova
   

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9. 30M
   50+ 500M
   APPS & GAMES MONTHLY USERS TOTAL SESSIONS
   With over 50 integrated apps, GetSocial serve 30
   million users every month that generated half a billion
   sessions during 2015.
   

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10. #dfua
    GetSocial SDK architecture
    Android
    SDK
    iOS
    SDK
    iOS Bridge Android Bridge
    C# API
    Unity SDK
    Java Objective C C#
    We have Android and iOS SDKs built
    natively using Java and Objective C
    respectively. Unity SDK is a thin
    bridge layer that forwards calls from
    public interface exposed in C# to
    native implementation
    

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11. #dfua
    GetSocial SDK architecture
    THE GOOD:
    • Easy to leverage all platform features
    • Doing work twice
    • Hard to keep in sync API behaviour
    THE BAD:
    The biggest advantage of having pure native SDK -
    being able to use low level platform features.
    Disadvantage - all features are implemented twice
    (longer time to market), also it’s hard to keep
    behaviour in sync, coz each developer has unique way
    to solve problems.
    

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12. –Sun Microsystems
    Write once, run everywhere
    “
    We decided to look around on possible solutions, to
    reach ultimate goal, write code once and run it
    everywhere.
    

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13. #dfua
    Requirements
    Maintainability
    Performance
    Size footprint Licensing
    Requirements for the solution:
    - performance should be at least the same as on native
    - code should be easy to maintain (reliable toolchain)
    - SDK should keep reasonable size
    - ideally solution should be free and compatible with
    our distribution model
    

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14. #dfua
    J2ObjC
    Xamarin XmlVM
    RoboVM
    We did a research on what tools were available on a
    market. Some were not performant enough, some
    were not suitable for SDK development.
    

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15. #dfua
    J2ObjC
    All except J2ObjC.
    Project started and actively developed by Google.
    Inbox built with J2ObjC.
    We started an internal RnD project to research if
    J2ObjC can fit with our requirements.
    

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16. #dfua
    Dive into J2ObjC
    Let’s look more close on the key features of J2ObjC.
    

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17. J2ObjC - WTF?
    Build configuration
    Development process
    Project impact
    The grand plan
    @zasadnyy
    

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18. #dfua
    What is J2ObjC?
    • Source-to-source compiler
    • Focus on shared business logic
    • Apache 2 Licence
    

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19. #dfua
    • NOT cross-platform application tool
    • NOT platform-independent UI toolkit
    • NOT Java emulator
    • NOT one time source translation
    What J2ObjC isn’t
    

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20. #dfua
    Is it production ready?
    v1.0.0
    January 21, 2016
    

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21. #dfua
    What is supported?
    • Full Java 7 syntax
    • Inner classes, enums, annotations…
    • Reflection
    • JUnit test translation
    • OCNI code embedding
    J2ObjC engineers did a great job, they reimplemented
    Java paradigms like inner classes, enums, annotations
    and reflection on Objective C, where they are not
    available.
    

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22. #dfua
    OCNI code embedding
    static native void log(String text) /*-[
    NSLog(@"%@", text); 

    ]-*/;
    Java code
    You can embed Objective C code in Java in a special
    comments.
    

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23. #dfua
    OCNI code embedding
    static native void log(String text) /*-[
    NSLog(@"%@", text); 

    ]-*/;
    + (void)log: (NSString*)text {

    NSLog(@"%@", text); 

    }
    Translated code
    DON’T do that, little bunnies die each time you’re using
    OCNI.
    

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24. #dfua
    Build configuration
    

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25. #dfua
    How to use
    $ j2objc DevFest.java
    $ ls
    DevFest.h DevFest.m
    translating DevFest.java
    Translated 1 file: 0 errors, 0 warnings
    j2objc is a command line tool, you’re going to work
    with to perform translation from Java to Objective C.
    It’s very powerful, but not very convenient to use on a
    real projects, coz amount of passed parameters will
    explode.
    

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26. #dfua
    Available plugins
    Make Eclipse Gradle
    Maven
    J2ObjC provide a plugins for most part of popular build
    tools.
    We’re going to focus on Gradle plugin.
    

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27. #dfua
    Gradle plugin
    • Easy integration
    • State of art codebase
    The good
    Bruno Bowden Advay Mengle
    • Rockstar authors
    

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28. #dfua
    Gradle plugin
    • As of July 25 is not supported
    • Last supported J2ObjC version is 0.9.8.2.1
    • Last supported Gradle version is 2.8
    • Check our fork at
    https://github.com/getsocial-rnd/j2objc-gradle
    The bad
    Main problem with j2objc-gradle plugin - it supports
    only Gradle up to v2.8. Android on the other hand to
    support latest features requires 2.9+. Big part of plugin
    need to be rewritten to support new project model
    introduced in 2.9.
    

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29. #dfua
    Setting up iOS project
    • Automatically via CocoaPods
    • Manually link binaries
    THE GOOD:
    THE BAD:
    • Impossible debug
    

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30. #dfua
    Setting up iOS project
    Xcode
    Project
    Default flow
    Java
    Source
    ObjC
    Source
    Static
    Library
    

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31. #dfua
    Setting up iOS project
    Xcode
    Project
    Java
    Source
    ObjC
    Source
    Static
    Library
    GetSocial solution
    Python
    script
    

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32. #dfua
    Build time optimisations
    • Build only debug binaries
    • Include only target processor architectures
    Default: ios_arm64,ios_armv7,ios_x86_64
    • Set up single platform builds
    

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33. #dfua
    6
    min
    <2
    min
    *Android + J2ObjC build
    GetSocial case
    Build time optimisations
    

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34. #dfua
    Development process
    

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35. #dfua
    Project structure
    workspace
    ├── build.gradle
    ├── android
    │ ├── android-demo/..
    │ └── android-library/..
    ├── ios
    │ ├── ios-demo/..
    │ ├── ios-library/..
    │ ├── ios-shared
    │ └── WORKSPACE.xcworkspace
    ├── lib
    │ ├── rx-java
    │ └── gson
    └── shared
    ├── src/..
    └── build.gradle
    Shared code
    GetSocial case
    

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36. #dfua
    Libraries sources
    Project structure
    workspace
    ├── build.gradle
    ├── android
    │ ├── android-demo/..
    │ └── android-library/..
    ├── ios
    │ ├── ios-demo/..
    │ ├── ios-library/..
    │ ├── ios-shared
    │ └── WORKSPACE.xcworkspace
    ├── lib
    │ ├── rx-java
    │ └── gson
    └── shared
    ├── lib/..
    └── src/...
    GetSocial case
    

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37. #dfua
    Project structure
    workspace
    ├── build.gradle
    ├── android
    │ ├── android-demo/..
    │ └── android-library/..
    ├── ios
    │ ├── ios-demo/..
    │ ├── ios-library/..
    │ ├── ios-shared
    │ └── WORKSPACE.xcworkspace
    ├── lib
    │ ├── rx-java
    │ └── gson
    └── shared
    ├── lib/..
    └── src/...
    iOS code
    GetSocial case
    

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38. #dfua
    Project structure
    workspace
    ├── build.gradle
    ├── android
    │ ├── android-demo/..
    │ └── android-library/..
    ├── ios
    │ ├── ios-demo/..
    │ ├── ios-library/..
    │ ├── ios-shared
    │ └── WORKSPACE.xcworkspace
    ├── lib
    │ ├── rx-java
    │ └── gson
    └── shared
    ├── lib/..
    └── src/...
    GetSocial case
    Android code
    

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39. #dfua
    

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40. #dfua
    J2ObjC enforces Clean Architecture
    THE GOOD
    

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41. #dfua
    Presentation
    Clean architecture
    Drivers
    Frameworks
    Domain
    Dependency
    Rule
    shared
    XXX-library
    XXX-demo
    

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42. #dfua
    Libraries
    • Sources required
    • Not all java packages implemented
    • Tests are highly recommended
    

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43. #dfua
    dependencies {
    compile ‘com.google.code.gson:gson:2.6.2’
    }
    j2objcConfig {

    autoConfigureDeps true

    }
    Libraries
    shared/build.gradle
    If OOS library has sources and test published together
    with a binaries, you can ask j2objc plugin to pull them
    and cross compile. But we managed to get it working
    only for Gson.
    

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44. #dfua
    workspace
    ├──...
    ├── lib
    │ └── rx-java
    │ └── build.gradle
    └── shared
    └── build.gradle
    GetSocial solution
    Libraries
    Set-up J2ObjC
    translation
    Include library
    project
    More universal way is to create a new project with
    library, set up j2objc cross compilation for a project
    and include it as a dependency into shared module.
    

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45. #dfua
    Check ported libs at j2objc-common-libs-e2e-test GitHub project
    Junit, Hamcrest, Mockito, Protobuf, Guava,
    Gson, Joda-time, commons-lang3, sqlighter-4
    PORTED:
    AssertJ, RxJava, http libraries, DI, …
    MISSING:
    Libraries
    

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46. #dfua
    Unit testing is the DNA of J2ObjC
    THE GOOD
    

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47. #dfua
    High test coverage is the only way
    to confidence
    THE BAD
    

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48. #dfua
    Testing
    • JUnit 3, 4
    • Hamcrest 1.3
    • Mockito 1.9.5
    Toolchain
    

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49. #dfua
    • Narrow selection of testing libs/frameworks
    • Util classes in tests are being executed => FAIL
    • Thread.sleep(0) hangs
    Testing
    The bad
    The easiest way to solve the problem with util classes
    being run as test is to agree on convention of Test
    suffix for all text classes + providing exclude pattern for
    tests in j2objc grade plugin config
    

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50. #dfua
    Name mangling
    package com.zasadnyy.reddit.model;
    public class RedditDataManager {…}
    @interface ComZasadnyyRedditModelRedditDataManager
    : NSObject
    Translates to
    Class names
    Check the demo repo for more examples
    

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51. #dfua
    Name mangling
    String foo(int i);
    - (NSString *)fooWithInt:(jint)i;
    Translates to
    METHODS
    

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52. #dfua
    Name mangling
    The good
    j2objcConfig {

    translateArgs '--prefixes', 'packagePrefixes.properties'

    translateArgs '--mapping', 'methodMapping.properties'

    }
    • @ObjectiveCName(“”)
    • Method/package mapping configurations
    Gradle plugin provides configuration closure to setup
    package and method names mappings
    

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53. #dfua
    Name mangling
    The bad
    RedditDataManager.init(Ljava/lang/String;)V =
    VzRedditDataManager initWithAppId:(NSString)appId
    Method mappings are fragile
    Any refactoring of the method or change in package
    mappings will break your method mapping configuration
    

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54. #dfua
    Name mangling
    GetSocial solution
    Package
    prefixes
    Set of
    wrappers
    +
    We ended up using package mapping + wrapping all
    generated code on the ObjC side
    

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55. #dfua
    Project Impact
    

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56. #dfua
    Performance
    Make simple computations on
    the array of 600 GPS coordinates 1,000 times
    Testing method:
    Computational
    Source: Medium post by Harry Cheung
    

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57. #dfua
    Computational
    Average iOS Computational Performance
    Swift 1.2
    J2ObjC
    J2ObjC (ARC)
    Xamarin
    RoboVM
    Time, s
    0 0,275 0,55 0,825 1,1
    Performance
    

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58. #dfua
    Make simple computations on
    the array of 600 GPS coordinates 10,000 times
    Testing method:
    Source: Medium post by Harry Cheung
    Performance
    Memory
    

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59. #dfua
    Peak iOS Memory Performance
    Swift 1.2
    J2ObjC
    J2ObjC (ARC)
    Xamarin
    RoboVM
    Usage, Mb
    0 5 10 15 20
    Performance
    Memory
    

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60. #dfua
    iOS app size impact
    3Mb Extra (1 target platform)
    Reduce size:
    • Include only required parts of jre_emul.a
    • Shrink unused Java code with Proguard
    3Mb is mainly a size of translated JRE library that
    should be included with your project.
    

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61. #dfua
    Team impact
    • iOS Developers have way less work
    • Developers should be familiar with both platforms
    

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62. #dfua
    At a glance
    

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63. #dfua
    At a glance
    • Unsupported Gradle plugin
    • Limitations on dependencies
    • Unit tests as the only way to validate logic
    THE BAD:
    

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64. #dfua
    At a glance
    THE GOOD:
    • Performance
    • Maintainability
    • Reasonable size footprint
    • Apache License
    • Clean architecture
    

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65. #dfua
    64%
    code reuse
    At a glance
    

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66. Thank you!
    Questions?
    Vitaliy Zasadnyy
    @zasadnyy
    Slides will be available at:
    v.zasadnyy.com/slides/
    Дякую за увагу!
    

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67. #dfua
    We are hiring ninjas!
    • Android (UA/NL)
    • Golang (UA)
    

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68. #dfua
    Resources
    • Official J2ObjC website
    • J2ObjC on GitHub
    • J2ObjC Gradle Plugin on GitHub
    • GitHub project with end-to-end test of compatible libraries
    • Goodow GitHub account with several J2ObjC related repos
    • Cross platform frameworks performance tests
    • Demo project
    

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