The document discusses migrating a Spring Boot application to use Java modules. It notes that while tool support is good, framework and library adoption of modules is still low. Migrating an application involves upgrading dependencies, compiling and running with Java 11+, preparing a module structure from bottom to up, and adding module descriptors. Key lessons are to test all paths during the migration, examine logs for answers, and recognize it is still pioneering work as adoption increases. The example application is split into modules for the application, REST API, domain, persistence, security, and external clients.

1. #SpringBootModules @JaapCoomans
Migrating your Spring Boot application to Java Modules
Jaap Coomans
@JaapCoomans

2. @JaapCoomans
Jaap Coomans
Developer / Software Architect
Java since 2002
Tilburg, The Netherlands
Father, husband
Boardgame player
about:me

3. JPMS: CURRENT STATE OF AFFAIRS

4. JPMS: CURRENT STATE OF AFFAIRS
Tool support: good

5. JPMS: CURRENT STATE OF AFFAIRS
Tool support: good
Framework and library adoption: low

6. JPMS: CURRENT STATE OF AFFAIRS
Tool support: good
Framework and library adoption: low
Developer adoption: very low

7. JPMS: CURRENT STATE OF AFFAIRS
Tool support: good
Framework and library adoption: low
Developer adoption: very low
What’s holding us back?

8. It’s like eating your
veggies…

9. It’s like eating your
veggies…
Yes, that’s better!

10. BUT

11. main
repositories
rest-apicontrollers
serviceslegacy
legacy-
framework
A TALE OF MISFORTUNE

12. main
repositories
rest-apicontrollers
serviceslegacy
legacy-
framework
A TALE OF MISFORTUNE

13. main
repositories
rest-apicontrollers
serviceslegacy
legacy-
framework
A TALE OF MISFORTUNE

14. https://www.flickr.com/photos/nasacommons/20264606661
What challenges will we face?

15. SPLIT PACKAGESSPLIT PACKAGES

16. Automatic
Modules
https://commons.wikimedia.org/wiki/File:Roborally_boardgame.JPG
Author: Moroboshi

17. AUTOMATIC MODULES

18. AUTOMATIC MODULES
Exports and opens all packages

19. AUTOMATIC MODULES
Exports and opens all packages
Reads all other modules

20. AUTOMATIC MODULES
Exports and opens all packages
Reads all other modules
Module name derived from filename

21. AUTOMATIC MODULES
Exports and opens all packages
Reads all other modules
Module name derived from filename
Automatic-Module-Name

22. What will we build?
Author: Yonghokim
https://commons.wikimedia.org/wiki/File:A_game_of_Settlers_of_Catan.jpg

23. application
rest-api
domain
persistencesecurity bgg-client
OpenFeignJJWT
JAX-B

24. application
rest-api
domain
persistencesecurity bgg-client
OpenFeignJJWT
JAX-B

25. Step 1
Upgrade your
dependencies
https://commons.wikimedia.org/wiki/File:Funkenschlag-detail2.jpg
Author: Matěj Baťha

26. Step 2
Run with
JDK11+
Author: Nodens77https://boardgamegeek.com/image/762747/el-grande
Author: Jérémie Bryon

27. Step 3
Compile with
JDK11+
https://boardgamegeek.com/image/273748/union-pacific
Author: Mark Hamburg

28. Step 4
Prepare module
structure
https://boardgamegeek.com/image/213002/saint-petersburg
Author: Ross G. (ZiggyZambo)

29. Step 5
Add descriptors
bottom-up
https://boardgamegeek.com/image/3158665/castles-mad-king-ludwig
Author: Steph Hodge

30. Step 6
Add descriptor
to main jar
https://boardgamegeek.com/image/2053387/camel
Author: Tomasz Miedzik

31. Bonus round:

32. LESSONS LEARNED

33. LESSONS LEARNED
GO BOTTOM UP

34. LESSONS LEARNED
Test all paths on every step
GO BOTTOM UP

35. LESSONS LEARNED
The logs have the answer
Test all paths on every step
GO BOTTOM UP

36. LESSONS LEARNED
It still involves pioneering
The logs have the answer
Test all paths on every step
GO BOTTOM UP

37. Game over…
Get the code:
Contact me:
https://github.com/jaapcoomans/spring-boot-modules
@JaapCoomans
jaap.coomans@group9.nl