Version Mgmt in MavenSOME BEST PRACTICES

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

Software Versioning Version identifies software artefacts:◦ modules, applications, assemblies, …◦ Uniquely identifies source code◦ Build should be repeatable from that version of code

Most used:◦ Major.minor[.bugfix][-qualifier[-build]]

Qualifiers:◦ 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

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!

Maven in a nutshell

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

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

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

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

Workspace POM Dummy Aggregator POM

Just to launch other POM’s

Can use symbolic links to point to actual application roots to be built.

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)

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

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

Module POM Defines all direct dependencies

◦ Do not rely on transitive dependencies◦ Use scopes when applicable

◦ Compile◦ Runtime (e.g. JDBC Drivers)◦ Test (e.g. JUnit, DBUnit)◦ Provided (e.g. Java EE jars)

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

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

Demo1 Command line release cascade

Jenkins demo

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?

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

What if… you version an application

system Only one version to manage

Release all at once

Every change need a full release

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

More interesting pluginshttp://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

Demo2 maven-help-plugin

maven-dependency-plugin

maven-versions-plugin

Questions