Designing for Modularity with Java 9

Transcription

1 Designing for Modularity with Java 9 Paul Sander

2 Today's journey Module primer Services & DI Modular design Layers & loading

3 Designing for Modularity with Java 9 What if we forget about the classpath... embrace modules... want to create truly modular software?

4 Designing for Modularity with Java 9 What if we forget about the classpath... embrace modules... want to create truly modular software? Design Constraints Patterns

5 A Module Primer module easytext.cli { requires easytext.analysis; module easytext.analysis { exports analysis.api; opens impl; easytext.cli easytext.analysis analysis.api reflection only! impl other

6 A Module Primer module easytext.cli { requires easytext.analysis; module easytext.analysis { exports analysis.api; Modules define dependencies opens impl; explicitly easytext.cli easytext.analysis analysis.api reflection only! impl other

7 A Module Primer module easytext.cli { Packages are encapsulated by default requires easytext.analysis; module easytext.analysis { exports analysis.api; opens impl; easytext.cli easytext.analysis analysis.api reflection only! impl other

8 A Module Primer module easytext.cli { requires easytext.analysis; Packages can be opened for deep reflection at run-time module easytext.analysis { exports analysis.api; opens impl; easytext.cli easytext.analysis analysis.api reflection only! impl other

9 Services

10 EasyText example easytext.gui easytext.cli analysis.api easytext.analysis.kincaid easytext.analysis.coleman

11 EasyText example easytext.gui easytext.cli analysis.api easytext.analysis.kincaid easytext.analysis.coleman

12 Encapsulation vs. decoupling Even with interfaces, an instance has to be created Analyzer i = new KincaidAnalyzer();

13 Encapsulation vs. decoupling Even with interfaces, an instance has to be created Analyzer i = new KincaidAnalyzer(); We need to export our implementation! :-( module easytext.kincaid { exports easytext.analysis.kincaid;

14 Reflection isn t a workaround Class myimpl = Class.forName( ); MyInterface i = myimpl.newinstance(); Package needs to be open module easytext.kincaid { opens easytext.analysis.kincaid;

15 Services to the rescue easytext.gui easytext.cli uses uses Module System provides provides easytext.analysis.kincaid easytext.analysis.coleman

16 Providing a service module easytext.analyzer.kincaid { requires easytext.analysis.api; provides javamodularity.easytext.analysis.api.analyzer with javamodularity.easytext.analysis.kincaid.kincaidanalyzer;

17 Implementing a service Just a plain Java class Not exported! public class KincaidAnalyzer implements Analyzer { public KincaidAnalyzer() public double analyze(list<list<string>> sentences) {

18 Consuming a service module easytext.cli { requires easytext.analysis.api; uses javamodularity.easytext.analysis.api.analyzer;

19 Consuming a service module easytext.cli { requires easytext.analysis.api; uses javamodularity.easytext.analysis.api.analyzer; Iterable<Analyzer> analyzers = ServiceLoader.load(Analyzer.class); for (Analyzer analyzer: analyzers) { System.out.println( analyzer.getname() + ": " + analyzer.analyze(sentences));

20 Finding the right service ServiceLoader supports streams Lazy instantiation of services ServiceLoader<Analyzer> analyzers = ServiceLoader.load(Analyzer.class); analyzers.stream().filter(provider -> ).map(serviceloader.provider::get).foreach(analyzer -> System.out.println(analyzer.getName()));

21 Add new analyses by adding provider modules on the module path

22 Dependency Injection

23 Providing a Guice service Provider module should export a Guice Module public class ColemanModule extends AbstractModule protected void configure() { Multibinder.newSetBinder(binder(), Analyzer.class).addBinding().to(ColemanAnalyzer.class);

24 Providing a Guice service Consumers must be able to compile against the Guice module Service impl package must be open module easytext.algorithm.coleman { requires easytext.algorithm.api; requires guice; requires guice.multibindings; javamodularity easytext algorithm coleman ColemanAnalyzer.java guice ColemanModule.java module-info.java exports javamodularity.easytext.algorithm.coleman.guice; opens javamodularity.easytext.algorithm.coleman;

25 Consuming a Guice service public class Main { public static void main(string... args) { Injector injector = Guice.createInjector( new ColemanModule(), new KincaidModule()); CLI cli = injector.getinstance(cli.class); cli.analyze(args[0]);

26 Consuming a Guice service Require the implementation Guice modules Open package for Guice injection module easytext.cli { requires easytext.algorithm.api; requires guice; requires easytext.algorithm.coleman; requires easytext.algorithm.kincaid; opens javamodularity.easytext.cli;

27 Consuming a Guice service Now we public class CLI { private final Set<Analyzer> public CLI(Set<Analyzer> analyzers) { this.analyzers = analyzers;

28 Injecting a service algorithm.coleman Create binding guice

29 Injecting a service Requires Guice module algorithm.coleman cli Create binding guice

30 Injecting a service Requires Guice module algorithm.coleman cli Create injector Create binding guice

31 Injecting a service Requires Guice module algorithm.coleman cli Create injector Create binding Inject instance guice

32 Services vs Guice Benefits of using vs using an API Developers might be more familiar the model Downsides of using Guice Requires more coupling Adding an implementation requires code changes

33 Services *and* Guice module easytext.algorithm.coleman { requires easytext.algorithm.api; requires guice; requires guice.multibindings; exports javamodularity.easytext.algorithm.coleman.guice; opens javamodularity.easytext.algorithm.coleman;

34 Services *and* Guice module easytext.algorithm.coleman { requires easytext.algorithm.api; requires guice; requires guice.multibindings; exports javamodularity.easytext.algorithm.coleman.guice; opens javamodularity.easytext.algorithm.coleman; provides com.google.inject.abstractmodule with javamodularity.easytext.algorithm.coleman.guice.colemanmodule

35 Services *and* Guice module easytext.cli { requires easytext.algorithm.api; requires guice; requires easytext.algorithm.coleman; requires easytext.algorithm.kincaid; opens javamodularity.easytext.cli;

36 Services *and* Guice module easytext.cli { requires easytext.algorithm.api; requires guice; requires easytext.algorithm.coleman; requires easytext.algorithm.kincaid; opens javamodularity.easytext.cli; uses com.google.inject.abstractmodule

37 Modular Design

38 Naming Modules... is hard

39 Naming Modules... is hard Application modules Short & memorable <application>.<component> e.g. easytext.gui

40 Naming Modules... is hard Application modules vs. Library modules Short & memorable <application>.<component> e.g. easytext.gui Uniqueness Reverse DNS com.mycompany.ourlib 'Root package'

41 API Modules

42 API Modules Module with exported API only When multiple implementations are expected Can also contain 'default' implementation

43 API Modules Module with exported API only When multiple implementations are expected Can also contain 'default' implementation API modules export: Interfaces (Abstract) classes Exceptions Etc.

44 Small Modules vs. All-in-one

45 Small Modules vs. All-in-one Small modules Composability Reusability

46 Small Modules vs. All-in-one Small modules Composability? Reusability?? All-in-one modules? Ease-of-use?

47 Small Modules vs. All-in-one Why choose? Use aggregator modules

48 Small Modules vs. All-in-one Why choose? Use aggregator modules Module without code, using implied readability: module mylib { requires transitive mylib.one; requires transitive mylib.two; requires transitive mylib.three;

49 Small Modules vs. All-in-one Why choose? Use aggregator modules Module without code, using implied readability: mylib module mylib { requires transitive mylib.one; requires transitive mylib.two; requires transitive mylib.three; mylib.one mylib.three mylib.two

50 Small Modules vs. All-in-one Why choose? Use aggregator modules mylib application mylib.one mylib.three mylib.two

51 Small Modules vs. All-in-one Why choose? Use aggregator modules mylib application mylib.one mylib.three mylib.two

52 Small Modules vs. All-in-one Why choose? Use aggregator modules mylib application mylib.one mylib.three Implied readability mylib.two

53 Small Modules vs. All-in-one mylib.extra mylib.core

54 Small Modules vs. All-in-one mylib.extra application mylib.core

55 Small Modules vs. All-in-one mylib.extra application mylib.core

56 Small Modules vs. All-in-one mylib.extra application mylib.core

57 Breaking cycles Non-modular JARs can have cyclic dependencies Modules can not

58 Breaking cycles

59 Breaking cycles public class Author { private String name; private List<Book> books; public Author(String name) { this.name = name; //..

60 Breaking cycles public class Author { private String name; private List<Book> books; public class Book { public Author author; public String title; public Author(String name) { this.name = name; //.. public void printbook() { System.out.printf( "%s, by %s\n\n%s", title, author.getname(), text);

61 Breaking cycles public class Author { private String name; private List<Book> books; public class Book { public Author author; public String title; public Author(String name) { this.name = name; //.. public void printbook() { System.out.printf( "%s, by %s\n\n%s", title, author.getname(), text);

62 Breaking cycles public class Author { private String name; private List<Book> books; public class Book { public Author author; public String title; public Author(String name) { this.name = name; //.. public void printbook() { System.out.printf( "%s, by %s\n\n%s", title, author.getname(), text);

63 Breaking cycles: abstraction

64 Breaking cycles: abstraction public class Author //.. implements Named { public String getname() { return this.name;

65 Breaking cycles: abstraction public class Author implements Named { //.. public String getname() { return this.name; public interface Named { String getname();

66 Optional dependencies Requires means compile-time and run-time dependency What if we want an optional dependency? Use it if available at run-time Otherwise, run without

67 Optional dependencies Requires means compile-time and run-time dependency What if we want an optional dependency? Use it if available at run-time Otherwise, run without Compile-time only dependencies: module framework { requires static fastjsonlib;

68 Optional dependencies Requires means compile-time and run-time dependency What if we want an optional dependency? Use it if available at run-time Otherwise, run without Compile-time only dependencies: module framework { requires static fastjsonlib; Resolve fastjsonlib if available at run-time, ignore if not

69 Optional dependencies Avoid run-time exceptions!

70 Optional dependencies Avoid run-time exceptions! try { Class<?> clazz = Class.forName("javamodularity.fastjsonlib.FastJson"); FastJson instance = (FastJson) clazz.getconstructor().newinstance(); System.out.println("Using FastJson"); catch (ReflectiveOperationException e) { System.out.println("Oops, we need a fallback!");

71 Optional dependencies Better yet: use services for optional dependencies module framework { requires json.api; uses json.api.json; ServiceLoader.load(Json.class).stream().filter(this::isFast).findFirst();

72 Layers and dynamic module loading

73 ModuleLayer Module path mods easytext.algorithm.api easytext.algorithm.coleman easytext.algorithm.kincaid easytext.algorithm.naivesyllablecounter easytext.algorithm.nextgensyllablecounter easytext.cli easytext.gui

74 ModuleLayer Module path mods easytext.algorithm.api easytext.algorithm.coleman easytext.algorithm.kincaid easytext.algorithm.naivesyllablecounter easytext.algorithm.nextgensyllablecounter easytext.cli easytext.gui boot layer api coleman... at run-time kincaid gui

75 ModuleLayer Immutable boot layer App & platform modules api coleman... One version of a module kincaid gui No dynamic loading?

76 ModuleLayer boot layer Create layers at run-time api Layers form hierarchy... gui Multiple versions in layers

77 ModuleLayer layer 1 coleman parent boot layer Create layers at run-time api Layers form hierarchy... gui Multiple versions in layers

78 ModuleLayer layer 1 coleman layer 2 kincaid syllable. counter parent parent Create layers at run-time api boot layer Layers form hierarchy... gui Multiple versions in layers

79 ModuleLayer Demo

80 Thank you. Paul Sander