The document discusses the importance of modularity in Java, highlighting its benefits such as strong encapsulation, reliable configuration, enhanced security, and footprint optimization. It uses AcmeAir, a fictitious airline, as an example to illustrate the application of modularity. Additionally, it provides links to related projects and specifications concerning modular Java development.

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Modularizing AcmeAirDinakar Guniguntala (@dinogun)
Sabari Krishnamoorthy (@devi__krish)
OpenJ9 Cloud Squad, Bangalore

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Agenda

Why Modularity ?

Modularity Goals

What is AcmeAir

Applying modularity to AcmeAir

Summary

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Why Modularity ?

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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.

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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.

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Modularity Goals

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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.

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Modular Java 9 JDK

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AcmeAir
A Fictitious Airline

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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)

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Demo
(https://github.com/ibmruntimes/acmeair-modular)

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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