The document discusses how to decrease application footprint using Java modules. Key points include: 1. Migrating a Spring Boot application to Java 9 modules by adding a module-info.java file and updating dependencies. No code changes were needed. 2. Lessons learned include automatic modules can cause issues, and third party libraries may need to open packages. 3. JDK 10 features like container awareness can reduce resource usage of Java applications running on Docker. Application class data sharing also improves startup times. 4. Modules in JDK 10 have a smaller memory footprint and faster startup times compared to non-module applications.

1. Java Module System
How to decrease your application footprint
Leonardo Zanivan - Crossover
Rodrigo Cândido da Silva - Integritas

3. Java9ModulesSystem

5. Previous Module System Classpath

6. After Module System Classpath
JDK9+

9. SpringModules

11. jlinkexec

12. ● Spring Boot 2 sample application with REST MVC & JPA
1. Create module-info.java with all the required imports
2. Update third party libs with JDK 9/10 fixes
3. Add new Maven plugin to copy dependencies
4. No Java code change was required
Migrating Spring PetClinic to Java 9 Modules

13. ● Application can still run with explicit classpath after migration
● Use --upgrade-module-path to override problematic modules
● You will find that third party libs are not ready to use modules
Lessons Learned

14. ● Automatic modules can cause issues (naming conflicts, JLink)
○ e.g: JLink was used to create a minimal JRE manually
● Third party libs may require you to open some packages
○ e.g: Hibernate JPA, Spring
● Hello World always work!
Lessons Learned

15. JDK 10 Highlights
Docker
awareness
JDK-8146115 enhancement
JDK-8186309 enhancement
JDK-8179498 enhancement
Can extract
container-specific
information about number
of CPUs (automatically)
Can extract
container-specific
information about
allocated memory
(automatically)
Attaching to namespace
issue(s) have been resolved!
host PID ⇒ container PID
New JVM flags for Docker support:
-XX:UseContainerSupport (default)
-XX:ActiveProcessorCount
-XX:InitialRAMPercentage
-XX:MaxRAMPercentage
-XX:MinRAMPercentage
Support for Linux only

16. JDK 10 Highlights
Reduce resource
footprint when
multiple JVMs were
running on the same
physical machine
JEP 310:
Application
Class-Data
Sharing
Pre-Java 10, use of CDS had
been restricted to the
bootstrap class loader only
Improve
startup time
of application Processes/applications can sharing
common class metadata
(class-data), from a shared archive
(CDS archive)

17. ● java.xml.ws (JAX-WS)
● java.xml.bind (JAXB)
● java.activation (JAF)
● java.xml.ws.annotation (JSR 250)
● java.corba (CORBA)
● java.transaction (JTA)
● java.se.ee (Aggregator module)
● jdk.xml.ws (Tools for JAX-WS)
● jdk.xml.bind (Tools for JAXB)
JDK 11 Changes
JEP 320:
Remove Java EE
and CORBA
Modules

18. Eclipse OpenJ9
● TL;DR; 2x smaller memory
footprint and starts 2x faster
than HotSpot.
● Experimental; AdoptOpenJDK
builds are available.
https://adoptopenjdk.net

19. github.com/panga/qcon2018-java9modules

20. Note: JDK 10 Alpine was built from source: https://hub.docker.com/r/panga/openjdk10/
JDK 10 Minimal JRE + Module Application < 100mb

21. Note: Best case scenario during my tests.
Limit: 2 cpus, 1g memory, JVM_OPTS= Xmx512m
JDK 10 Modules starts 2x faster on Docker

22. Note: Best case scenario during my tests.
JMeter test plan was used to load application.
JDK 10 Modules has 2x lower footprint on Startup!

23. JDK 10 Modules has 2x lower footprint after Load!
Note: Best case scenario during my tests.
JMeter test plan was used to load application.

24. github.com/panga/spring-petclinic-java9modules

25. @leonardopanga
@rcandidosilva
http://jav.mn/java10