Java 9 introduces modularity as a feature. This helps the JDK to be more scalable down to small computing devices as well as in the cloud where a lower size helps reduce the provisioning and the deploy times. It also helps to improve the security of the JDK and avoid Classpath hell! We pick Acme Air, a popular open source benchmark that implements a fictitious airline and convert it into a modular application. This tutorial walks through the various hurdles while converting the micro services version of the AcmeAir to be modular, working with build tools such as Gradle, using jdeps and handling third party modules.

1. IBM Runtime TechnologiesIBM Runtime Technologies
Modularizing AcmeAirDinakar Guniguntala (@dinogun)
Sabari Krishnamoorthy (@devi__krish)
OpenJ9 Cloud Squad, Bangalore

2. IBM Runtime TechnologiesIBM Runtime Technologies
2
Agenda

Why Modularity ?

Modularity Goals

What is AcmeAir

Applying modularity to AcmeAir

Summary

3. IBM Runtime TechnologiesIBM Runtime Technologies
3
Why Modularity ?

4. IBM Runtime TechnologiesIBM Runtime Technologies
4
Classpath/jar Hell
●
The same class is
available from two or
more jar files.
●
These classes may have
been pulled in
automatically from the
build tool when trying
to resolve
dependencies.
●
The two versions may
behave differently.

5. IBM Runtime TechnologiesIBM Runtime Technologies
5
Security/Footprint

Typical JRE size is around
~200MB - 250MB

The JRE carries a lot of legacy
code.

The percentage of code from
the JRE that is actually used by
any application is very small
compared to the functionality
packaged in the JRE.

No easy way to reduce the size
of the JRE.

TCK compliance is another
aspect to be considered while
chopping the JRE to suit one's
need.

6. IBM Runtime TechnologiesIBM Runtime Technologies
6
Modularity Goals

7. IBM Runtime TechnologiesIBM Runtime Technologies
7
Modularity Goals

Strong Encapsulation
– Only expose the interfaces that are to be used by external modules.
– Internal implementation details are truly hidden.

Reliable configuration
– Module system makes it easy to understand the dependencies and the interfaces exported.
– Compile and runtime dependency checks reduces run-time errors.

Security
– No longer possible to access internal classes, helps reduce vulnerabilities.

Footprint optimization
– Jlink helps to package only those modules that are needed. Greatly reduces the size of the runtime.

8. IBM Runtime TechnologiesIBM Runtime Technologies
8
Modular Java 9 JDK

9. IBM Runtime TechnologiesIBM Runtime Technologies
9
AcmeAir
A Fictitious Airline

10. IBM Runtime TechnologiesIBM Runtime Technologies
10
AcmeAir – Non-modular layout
acmeair-services
acmeair-mongo-servicesacmeair-loader
javaee-web-api
json-simple
mongo-java-driver
bson
acmeair-ss
(Support Service)
acmeair-mainapp
(Web) acmeair-bs
(Booking Service)
acmeair-fs
(Flight Service)
acmeair-cs
(Customer Service)
Maven Repo
acmeair-as
(Authentication)

11. IBM Runtime TechnologiesIBM Runtime Technologies
11
Demo
(https://github.com/ibmruntimes/acmeair-modular)

12. IBM Runtime TechnologiesIBM Runtime Technologies
12
Related Links

Related JEPs and JSRs

http://openjdk.java.net/projects/jigsaw/
– 200: The Modular JDK → http://openjdk.java.net/jeps/200
– 201: The modular source code → http://openjdk.java.net/jeps/201
– 220: The modular Run-Time images → http://openjdk.java.net/jeps/220
– 260: Encapsulate most internal APIs → http://openjdk.java.net/jeps/260
– 261: Module System → http://openjdk.java.net/jeps/261
– 282: jlink: The java linker → http://openjdk.java.net/jeps/282

Gradle modularity changes
– https://guides.gradle.org/building-java-9-modules/
– https://discuss.gradle.org/t/modularity-support-with-gradle/22445