Modularisation in Java 9 splits the Java language and JDK/JRE into modules. This includes modularising the OpenJDK source code and runtime images to improve structure, reduce dependencies, and allow for smaller custom runtimes using jlink. The Java Platform Module System (JSR 376) introduced modules that define dependencies and exported/opened packages, allowing Java code and the JDK to be modularized. Hands-on sessions demonstrated creating modules, using jlink to build custom runtimes, and migrating non-modular code to Java 9.

1. Java 9 / Jigsaw
Modularisation & more

2. Presenters
Simon Maple
@sjmaple
Mani Sarkar
@theNeomatrix369
Hendrik Ebbers
@hendrikebbers

3. Our guest
Heather VanCura
@heathervc

4. Agenda
- Session 1: Introduction
- What is meant by Modularisation in Java 9?
- Session 2: JLink
- Lunch break: lunch + 10/15 minute optional session
- Fundamentals and background
- JSRs / JEPs playing a role
- Modularisation of OpenJDK sources (JEP 201 and related JEPs)
- Modularisation of Runtime Images (JEP 220 and related JEPs)
- Modularisation of Java Packages and Application Packaging (JEP 275 and related JEPs)
- Feature distribution
- Why modularisation?
- So many more topics to cover!
- Visualise your dependencies!
- Session 3: Migrating non-modular app to Java 9 or JShell
- Feedback
- Contribution
- Resources

5. How to share your (live) feedback with us?
Discussion/technical corner, share your thoughts, code snippets,
issues, feedback with us while you code away...
https://goo.gl/oytFzX
We have left a few
issues for you to find,
investigate, solve, report
to us or the OpenJDK /
JDK9 team

6. Setup
Is everyone setup, and ready to go?
https://git.io/v9UJ8
You have this link via email / meetup message!

7. Session 1: Introduction: Java 9 modularisation
15 minutes

8. What is meant by Modularisation in Java 9?
JDK
module java.base
package java.io
class Console
...
package java.lang
class String
...
module java.logging
package java.util.logging
class FileHandler
class LogManager
...
module java.sql
package java.sql
class Connection
class SqlData
...
Java, the language: split into modules
modules...
packages...
classes...

9. What is meant by Modularisation in Java 9?
java.base
java.sql
other
modules...
java.logging
Java, the language: dependency graph
java.xml
implicit implicit
explicit
(requires)
explicit
(requires)
implicit
JDK

10. What is meant by Modularisation in Java 9?
Java, the language: dependency graph
java.base
java.sql
other
modules...
java.logging java.xml
implicit implicit
explicit
(requires)
explicit
(requires)
implicit
JDK
Our Java
applications
explicit
(requires)
explicit
implicit

11. What is meant by Modularisation in Java 9?
Pre-Java 9
Java 9/Jigsaw
src/main/java
package a.b.c
class p
class q
package m.n.o
class s
class t
src/main/java
module a.b.c
package a.b.c
class p
class q
module m.n.o
package m.n.o
class s
class t
Structure of
a typical
Java app.
containing
packages...
Create your own
modules
containing
packages, classes...

12. What is meant by Modularisation in Java 9?
Typical package structure Modules contain packages
Credits to Paul Bakker & Sander Mak
package books.api.entities
classes
package bookstore.api.service
What is looks like from the file system?

13. What is meant by Modularisation in Java 9?
Typical package structure Modules contain packages
Credits to Paul Bakker & Sander Mak
contains module
visibility
(readability) &
dependency info
module books.api contains
package books.api.entities
package books.api.service
modules
What is looks like from the file system?

14. What is meant by Modularisation in Java 9?
module com.abc {
requires com.abc.pqr;
requires transitive com.xyz.abc;
exports com.abc.def.alpha;
exports com.abc.pqr.beta to
com.ijk.mno,
com.lmn.stu;
uses java.network.Driver;
provides java.sql.Driver with com.mno.def.Driver;
}
module
definition
defines dependencies of module, to modules
com.abc.pqr & com.xyz.abc
transitive keyword defines
implicit dependency
module name
How is module dependencies are defined in Java 9?
module-info.java

15. What is meant by Modularisation in Java 9?
module com.abc {
requires com.abc.pqr;
requires transitive com.xyz.abc;
exports com.abc.def.alpha;
exports com.abc.pqr.beta to
com.ijk.mno,
com.lmn.stu;
uses java.network.Driver;
provides java.sql.Driver with com.mno.def.Driver;
}
module
definition
make all & only public types in specified
packages available to other modules
How is module dependencies are defined in Java 9?
module name
… or make available
to specified modules
module-info.java

16. What is meant by Modularisation in Java 9?
module com.abc {
requires com.abc.pqr;
requires transitive com.xyz.abc;
exports com.abc.def.alpha;
exports com.abc.pqr.beta to
com.ijk.mno,
com.lmn.stu;
uses java.network.Driver;
provides java.sql.Driver with com.mno.def.Driver;
}
module-info.java
module
definition
this module publishes
a service provider
this module uses a service provider
published by another module
module name
How is module dependencies are defined in Java 9?

17. Session 1: Hands-on: Java 9 modularisation
60 minutes
https://github.com/AdoptOpenJDK/jdk9-jigsaw/tree/master/session-1-jigsaw-intro

18. Session 1: feedback
15 minutes
https://goo.gl/oytFzX

19. Lunch break
60 minutes
Short 10/15 minutes covering intro/background/fundamentals (talk while having a bite of food and drink)

20. What is meant by Modularisation in Java 9?
A bit of fundamentals and background before we get to the answer

21. What is meant by Modularisation in Java 9?
modularisation
Pre-Java 9 Java 9
Anomalies
OpenJDK& JDK

22. What is meant by Modularisation in Java 9?
How we perceive the JDK/JRE from a developer’s / end-user’s perspective?
JDK or
JRE
IBM
Other
vendors
Oracle download
Create
Client
Apps
distribute
Client
Apps +
bundle
JRE

23. What is meant by Modularisation in Java 9?
How the maintainers of Java perceive it?
Distribute
built apps
+ bundle
JDK
IBM
Other
vendors
Oracle build downloadOpenJDK JDK

24. What is meant by Modularisation in Java 9?
Modularisation of OpenJDK sources (JEP 201 and related JEPs)
Binary
compatible
JDK
re-organise rebuild
OpenJDK
source
Refactored
OpenJDK
source
Repository
JDK
re-organise
Improved layout of
source folders in
the JDK repository

25. What is meant by Modularisation in Java 9?
Modularisation of Runtime Images (JEP 220 and related JEPs)
Binary
compatible
JDK
re-organise rebuild
Runtime
JDK
Optimised
(modular)
JDK
Runtime
Traditional
Runtime JDK
Image
re-organise
A more compact
Runtime JDK Image

26. What is meant by Modularisation in Java 9?
Modularisation of Java Packages and Application Packaging (JEP 275 and related JEPs)
Modular Java 9
application +
custom JDK
compiles creates
Modularised
JDK Runtime
Modular
Java 9
source
JLink Smaller JDK footprint
Java 9
applicationcompiles creates
Modularised
JDK Runtime
Non-modular
Java 9 source
Binary compatible
creates

27. What is meant by Modularisation in Java 9?
JSR 376: Java Platform Module System played the primary role
http://openjdk.java.net/projects/jigsaw/spec/

28. What is meant by Modularisation in Java 9?
JEPs that lead to all the new features in Java 9 (including
Jigsaw):
- 200: The Modular JDK
- 201: Modular Source Code
- 220: Modular Run-Time Images (depends on JEP 162)
- 260: Encapsulate Most Internal APIs (no dependencies)
- 261: Module System (dependens on JEP 220, related to JEP 238)
- 282: jlink: The Java Linker (replaces implementation of JEP 220)
- 275: Modular Java Application Packaging
- 222: jshell: The Java Shell (Read-Eval-Print Loop)
- 193: Variable Handles
- 110: HTTP 2 Client
- 238: Multi-Release JAR Files
- 158: Unified JVM Logging
- G1 related JEPs (3)
- JEPs related to a number of security improvements
- JEPs related to a number of platform improvements
- >>> Many, many more JEPs, see the Java 9 JEPs list for further details <<<

29. What is meant by Modularisation in Java 9?
JDK 9& Jigsaw feature distribution
...
Other
JDK 9
features
Jigsaw
...
...
...
... ... ... ...
...
...
...
...
...
...
...
...

30. Why Modularisation in Java 9?
But, why?

31. It’s been worked on for about a decade:
- Encapsulation (hiding away what’s not intended or necessary for public use)
- JDK internal APIs (sun.misc.unsafe, security, etc…)
- Our APIs
- Decluttering of code bases (loose coupling & high cohesion)
- OpenJDK sources
- JDK sources
- Our Java App sources (post migration and refactoring)
- Customised runtime JDK (smaller footprint)
- Highly desirable for IoT, arduino/embedded devices, etc…
- Improve distribution and runtime performance
- OSGi has it, why not in native Java?
- Any more?
Why Modularisation in Java 9?

32. Not everything can be covered but let’s find out about these topics:
- open module
- open package
- named and unnamed modules
- difference between classpath and module path
- automatic module names
- kill switch (remove Jigsaw restrictions)
- a CLI flag passed to java: java --permit-illegal-access …
- Jlink CLI option: --launcher
- and many more topics...
So many things to cover!

33. https://github.com/accso/java9-jigsaw-depvis
Visualise your dependencies!

34. Session 2: Introduction: JLink
10 minutes

35. Session 2: Introduction: JLink
Create a package
distributable, that
runs on any platform,
but needs a platform
specific JDK
JDK (javac)
Your App
packages
& classes
Your App
package
(distributable)
JVM, the
Platform
Java, the
language
(packages &
classes)
Any JRE/JDK
compiles
creates
Pre-Java 9
depends on (needs), to run

36. Session 2: Introduction: JLink
JDK
modules
JLink
JVM, the
Platform
Java, the
language (JDK
modules)
Your App
modules
Create standalone
distributable (smaller
footprint), that runs
on a specific platform
Your App
modules
JDK compiles
creates
Java 9

37. Session 2: Hands-on: JLink
40 minutes
https://github.com/AdoptOpenJDK/jdk9-jigsaw/tree/master/session-2-jlink

38. Session 2: feedback
10 minutes
https://goo.gl/oytFzX

39. Session 3: Introduction: Migration or JShell
15 minutes

40. Session 3: Introduction: Migration or JShell
Hendrik Ebbers
@hendrikebbers
Over to
Hendrik

41. Session 3 hands-on: Migration or JShell
60 minutes
https://github.com/AdoptOpenJDK/jdk9-jigsaw/tree/master/session-3-jshell

42. Session 3 & overall: feedback
15-30 minutes
https://goo.gl/oytFzX

43. Contribute
Don’t like something or like something a lot,
want to contribute to make things better?
https://adoptopenjdk.gitbooks.io/adoptopenjdk-getting-started-kit/content/en/how-to-navigate/how_to_contribute_to_adopt_openjdk_and_openjdk.html

44. Feedback
We value your feedback, make Java better
with your constructive feedback
https://adoptopenjdk.gitbooks.io/adoptopenjdk-getting-started-kit/content/en/feedback.htm
l

45. Resources
Want to know about the other features of Java 9:
https://github.com/AdoptOpenJDK/jdk9-jigsaw/blob/master/Java-9-Resources.md

46. Thank you to all
Thank you for your continued support
9
@virtualJug
@ljcjug
@hackthetower
@adoptopenjdk
@openjdk
@jcp_org
@java