1. Version Mgmt in
Maven
SOME BEST PRACTICES

2. Agenda
What is software versioning
How can maven help us?
◦ Maven release plugin
Best practices
◦ What to version?
◦ How to manage versions?
Tips and tricks
◦ Version handling with maven-versions-plugin
◦ Dependency analysis with maven-dependency-plugin

3. Version identifies software artefacts:
Software Versioning
◦ modules, applications, assemblies, …
◦ Uniquely identifies source code
◦ Build should be repeatable from that version of code
Most used:
◦ Major.minor[.bugfix][-qualifier[-build]]
Qualifiers:
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Alpha: not feature complete
Beta: contains critical bugs
CR: release candidate, not fully tested
Final: final version
SNAPSHOT
◦ Floating version, not an actual identification
◦ Should allways be used for code under development

4. Versioning with Source Code
Management
Basics of SCM (Git, Subversion, CVS, …)
◦ Synching software changes between developers
◦ Allowing multiple branches to be developed simultaneously
◦ Maintenance branches
◦ Feature branches
◦ Merge branches again 
◦ Tagging versions of code
◦ So you can find out later which bugs you solved when
SCM does not put a version number in your artifacts!

6. Maven in a nutshell

7. Maven Basics
Convention over configuration
◦ Convention for source code organization
◦ src/main/java
◦ src/webapp
◦ src/test/java
◦ Plugins with default configurations
◦ Jar, war, ear
◦ Surefire tests
◦ Reporting
Dependency Management
◦ Remote repository and local repository
◦ Transactional dependencies

8. Snapshots
In maven, versions under development have classifier ‘-SNAPSHOT’
◦ When building versions on a development system, you should always build SNAPSHOTS.
◦ When depending on a SNAPSHOT version of another module, maven will give you the latest
(timestamped) version
◦ Could give surprises of code that suddenly stops building
◦ Preferrably have the source code of your SNAPSHOT dependencies built locally
Non SNAPSHOT versions should be built only once and deployed once
◦ Should be tagged in Subversion/Git/CVS, and never changed
◦ (Unless you know for sure nobody got a copy yet)
◦ Released versions should never have SNAPSHOT dependencies
◦ See release plugin later

9. Organizing Maven Modules
Aggregator POM vs. Parent POM
◦ Aggregator POM organizes build of multiple modules
◦ One per subfolder
◦ Declares which subfolders contain modules
◦ Parent POM centralizes common configuration
◦ Plugin configuration
◦ Dependencies
◦ Dependency Management
Convention: Aggregator POM == Parent POM
◦ Exceptions are allowed

10. Typical Maven Workspace Hierarchy
Workspace POM
◦ Godfather aka archon (development team)
◦ Application System(s) (set of related applications)
◦ Application or Library
◦ Module Group(s) (if necessary)
◦ Module

11. Workspace POM
Dummy Aggregator POM
Just to launch other POM’s
Can use symbolic links to point to actual application roots to be built.

12. Godfather POM
Defines <distributionManagement> and <repositories>
◦ <distributionManagement>: where your artifacts are deployed
◦ <repositories>: where other necessary artifacts can be found
Rarely changes
◦ Simple fixed version number, e.g. 1, 2, 3, …
Do not put shared dependencies here
◦ Use maven import (since maven 2.0.9)

13. Application System POM
Inherits from Godfather
Defines external dependency versions in <dependencyManagement>
Defines common plugin configuration
◦ E.g. java compiler version
Could build an assembly containing all applications

14. Application or Library POM
Module groups
Defines internal dependency management
◦ Sibling modules
◦ Can use ${project.version}
Define more shared configuration
◦ Inapplicable on a higher level
◦ E.g. aspect jars to use

15. Module POM
Defines all direct dependencies
◦ Do not rely on transitive dependencies
◦ Use scopes when applicable
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Compile
Runtime (e.g. JDBC Drivers)
Test (e.g. JUnit, DBUnit)
Provided (e.g. Java EE jars)

16. Maven release plugin
mvn release:prepare release:perform
◦ Verifies if you checked in everything
◦ Verifies if you have SNAPSHOT dependencies
◦ outside the current released modules
◦ Tries to build and test your modules
◦ Updates the version to the release version and tags it in SCM
◦ Recursively
◦ Checks out the tagged version and build and deploys the release version
◦ Updates the version to the next SNAPSHOT version and checks it in
◦ Recursively

17. Maven release plugin prerequisites
<distributionManagement>
◦ in godfather POM
◦ point to repository server (nexus)
<server> with login for repository
◦ authorized to deploy
◦ in settings.xml
<scm> tag
◦ Point to subversion/git/CVS

19. Demo1
Command line release cascade
Jenkins demo

20. What to Version / What to release
Could be: Individual Modules, Applications, Application System?
Depends on the lifecycle of your product
◦ Do you want to deploy/upgrade a single module or application?
◦ Can you test a single module?
◦ Can you test an application without testing the rest of the application system?
◦ Can you trace bugs in one application without knowing what other applications are running?

21. What if…
you release individual modules
Every module can have its own version
Maintenance releases with individual modules
◦ Dependants can stick to release versions if they want
◦ For big refactorings you need snapshot dependencies
Need big cascaded release to build a new version

22. What if…
you version an application system
Only one version to manage
Release all at once
Every change need a full release

23. Mix and match
Release some individual modules
◦ Those that are used in multiple applications
Release some applications as a whole
◦ Applications in maintenance
Release some application systems
◦ With strong intra-application dependencies

24. More interesting plugins
http://maven.apache.org/plugins/index.html
maven-help-plugin
◦ mvn help:effective-pom
maven-dependency-plugin
◦ mvn dependency:tree
◦ mvn dependency:analyze
◦ mvn dependency:analyze-dep-mgmt
maven-versions-plugin
◦ mvn versions:use-next-snapshots -DexcludeReactor=false -Dincludes=group:*
◦ mvn versions:update-child-modules

25. Demo2
maven-help-plugin
maven-dependency-plugin
maven-versions-plugin

26. Questions