With Java 9, modularity comes to your doorstep (whether you ordered it or not). This isn't your average language feature: making the most out of it may involve rewiring your brain. In this session we explore the benefits of a modular codebase using Java 9 modules. Because who doesn’t like more reliable and secure applications, meanwhile killing the dreaded classpath? After reviewing the basic concepts of modules, we'll explore modularity patterns that enhance your design and development skills. We all have existing software, so migration of codebases to a modular world is an important topic as well. Automatic modules and other new concepts are added to your toolbox to this end. Want examples? We've got plenty in this practical and code-driven talk. Even if you intend to use Java 9 without modules, this talk helps you prevent common issues. You'll be ready for Java 9 before you know it. Both speakers are currently writing “Java 9 Modularity” for O’Reilly, expected early 2017. They have extensive experience under the belt already with the Java 9 Jigsaw early access builds.

1. By Sander Mak
Java 9 Modularity
in Action
@Sander_Mak

2. Today's journey
Modularity matters
Java 9 modules
Services
Migration
Linking

3. Modularity matters
Modularity is the ultimate
agile tool

4. Good fences
make good neighbours
Hide your internals!
Service contract
Module

5. Work in progress,
almost there now.
Java 9: Jigsaw, JSR-376

6. Goals
‣ Modularise the JDK
‣ Reliable application composition
‣ Strong encapsulation - hide platform internals
‣ Improved security
Current status
‣ JDK 9 modularised
‣ JSR 376 prototype (Jigsaw)
‣ Spec in final draft

7. History of Jigsaw
JSR-277
Java
Module
System
2005 2006 2011 2014
JSR-294
Improved
Modularity
Support
Java 7:
No Jigsaw
Java 8:
No Jigsaw
JSR-376
Java Platform
Module
System
JSR-291
'OSGi 4.1'

8. Something happened in May...
Java 9: Jigsaw, JSR-376

9. Drama, intrigue, politics

10. Drama, intrigue, politics
JCP
Executive
Committee

11. Drama, intrigue, politics
JCP
Executive
Committee

12. JEP 200: The Modular JDK

13. Goodbye classpath
Reliable configuration

14. Goodbye classpath
Modules with explicit dependencies
my.module
requires
other.module

15. Strong encapsulation
Hide your internals
java.base
java.lang
java.time
java.util
com.sun.*
sun.*
jdk.internal.*
my.module
requires
Access checks at VM level (even reflection)

16. Why not just use OSGi?
‣ OSGi is built on top of the JVM
‣ Can’t be used to modularise the JDK itself

17. Why not just use OSGi?
‣ OSGi is built on top of the JVM
‣ Can’t be used to modularise the JDK itself
Why not only modularise the JDK?
‣ Fair point :-)
‣ OSGi has never seen mass adoption, Java 9 will
bring modularity to all of us

18. Demo: EasyText
Analyze text complexity
easytext.cli
easytext.analyis
requires

19. Contracts & Services
MyInterface i = new MyImpl();
How to use code
that you can’t access?

20. Contracts & Services
Provider
module
Service
Registry
Consumer
module
Register
service
Lookup
service
Return
service
instance
Use an interface as contract

21. JSR-376 services
module myApi {
exports com.api;
}

22. JSR-376 services
module myApi {
exports com.api;
}
module myConsumer {
requires myApi;
uses com.api.MyService;
}

23. JSR-376 services
module myApi {
exports com.api;
}
‣ Services resolved and wired by modular runtime
‣ Use with 'enhanced' ServiceLoader API
module myConsumer {
requires myApi;
uses com.api.MyService;
}
module myProvider {
requires myApi;
provides com.api.MyService
with myProvider.MyServiceImpl;
}

24. JSR-376 services
module myApi {
exports com.api;
}
‣ Services resolved and wired by modular runtime
‣ Use with 'enhanced' ServiceLoader API
module myConsumer {
requires myApi;
uses com.api.MyService;
}
module myProvider {
requires myApi;
provides com.api.MyService
with myProvider.MyServiceImpl;
}
Iterable<MyService> services =
ServiceLoader.load(MyService.class);
for(MyService svc: services) {
svc.doSomething();
}

25. Extensibility
Demo: EasyText

26. Extensibility
Multiple algorithms:
‣ Flesch-Kincaid
‣ Coleman-Liau
Demo: EasyText

27. Extensibility
CLI & GUI?
Multiple algorithms:
‣ Flesch-Kincaid
‣ Coleman-Liau
Demo: EasyText

28. easytext.algorithm.api
easytext.algorithm.kincaid
easytext.algorithm.coleman
easytext.cli
easytext.gui
Demo: EasyText
javafx.controls
JDKApplication
javafx.graphics

29. easytext.algorithm.api
easytext.algorithm.kincaid
easytext.algorithm.coleman
easytext.cli
easytext.gui
Demo: EasyText
javafx.controls
JDKApplication
ServiceLoader
javafx.graphics

30. JSR-376 linking
‣ Use a linking tool (jlink) to create a custom 'runtime
image' with only the modules you need
‣ Uses explicit dependencies from module-info.class
‣ Allows for whole-program optimization
Runtime image
java.base
java.desktop
my.mod1
my.mod2
JVM

31. Demo: EasyText linking

32. ‣ Use jdeps to audit your code
‣ Escape hatch:
--add-exports java.base/javax.security.auth.x500=mymod
Preparing for Java 9

33. ‣ Use jdeps to audit your code
‣ Escape hatch:
--add-exports java.base/javax.security.auth.x500=mymod
Preparing for Java 9
‣ Gradual migration possible
‣ Mix classpath & modulepath
‣ Automatic modules

34. Top down migration
commons.lang3.3.4.jar demonstrator.jar
classpath
java.base module path

35. package com.javamodularity.demonstrator;
import org.apache.commons.lang3.StringUtils;
public class Demo {
public static void main(String args[]) {
String output = StringUtils.leftPad("Leftpad FTW!", 20);
System.out.println(output);
}
}
Classic classpath

36. package com.javamodularity.demonstrator;
import org.apache.commons.lang3.StringUtils;
public class Demo {
public static void main(String args[]) {
String output = StringUtils.leftPad("Leftpad FTW!", 20);
System.out.println(output);
}
}
Classic classpath
javac -cp lib/commons-lang3-3.4.jar
-d out $(find src -name '*.java')
java -cp out:lib/commons-lang3-3.4.jar
com.javamodularity.demonstrator.Demo
Compile
Run

37. Top down migration
commons.lang3.3.4.jar demonstrator.jar
classpath
java.base module path

38. Top down migration
commons.lang3.3.4.jar
demonstrator.jar
classpath
java.base module path
Can’t reference the classpath
from named modules!

39. Top down migration
demonstrator.jar
classpath
java.base module path
commons.lang
But this isn’t our code!

40. Automatic Modules
‣ A plain JAR on the module path becomes an
Automatic Module
‣ Module name derived from JAR name
‣ Exports everything
‣ Reads all other modules

41. module demonstrator {
requires commons.lang;
}
Using Automatic Modules

42. module demonstrator {
requires commons.lang;
}
Using Automatic Modules
javac --module-path lib
--module-source-path src
-d mods $(find src -name '*.java')
java --module-path mods:lib
-m demonstrator/com.javamodularity.demonstrator.Demo
Compile
Run

43. Java 9 release
July 27th 2017

44. Java 9 release
July 27th 2017

45. Java 9 release
July 27th 2017
September 21st 2017
No promises :-)

46. ‣ JSR-376 forces module-aware tooling
‣ Modularity throughout all
development phases
Java 9's promise

47. ‣ JSR-376 forces module-aware tooling
‣ Modularity throughout all
development phases
Java 9's promise
Spotlight on modularity == good

48. Thank you.
bit.ly/java9book
@javamodularity

49. Thank you.
bit.ly/java9book
@javamodularity
40% discount:
AUTHD

50. bit.ly/java9book
@javamodularity
bit.ly/java9course
Java 9 Modularity: First Look
Thank you.40% discount:
AUTHD