@rodrigograciano @CGuntur Apache Maven 4 … is awesome Chandra Guntur & Rodrigo Graciano Apr. 2024 1

@rodrigograciano @CGuntur • a powerful build management tool • primarily used to build Java projects • developed in Java • an open source project • follows convention-over-configuration • allows for other language projects to be built What is Apache Maven? 2

@rodrigograciano @CGuntur What is “convention-over-configuration”? • a software design paradigm • decreases the number of decisions needed from developer • satisfies the principle of least astonishment • provides sensible default “assumptions” • promotes common structures and flow in a project • an example: directory structure • not just limited to directory structure • instruction set for Apache Maven is via a POM 3

@rodrigograciano @CGuntur What is a POM? 4

@rodrigograciano @CGuntur “POM” is … A Pomeranian? Pomegranate Juice? One of the Pom-poms? 5

@rodrigograciano @CGuntur “POM” is … A pomeranian? Pomegranate Juice? One of the pom poms? • POM lists: • dependencies • plugins • properties • inheritance details • profiles • ... POM is Project Object Model 6

@rodrigograciano @CGuntur “POM” is … Appendix has POM structure details … 7

@rodrigograciano @CGuntur Benefits/usage of Apache Maven? 8

@rodrigograciano @CGuntur Benefits of using Apache Maven • visibility - build logs as evidence • reusability - builds can have composition & hierarchies • verifiability - builds produce test evidence • reproducibility - repeatable builds • maintainability - management of builds is possible • comprehensibility - ease of understanding the build process 9

@rodrigograciano @CGuntur How does Apache Maven work? 10

@rodrigograciano @CGuntur Watch for notes here How does Apache Maven work? Internet Maven Repository Java (or other lang) Project App Source Code 11

@rodrigograciano @CGuntur Watch for notes here How does Apache Maven work? (1) Internet Maven Repository Java (or other lang) Project Project Object Model (POM) assemble dependencies plugins profiles lifecycle build phases App Source Code • Add a pom (typically a pom.xml file) • Point settings.xml to repository • Include dependencies & plugins • Add properties & override configuration Notes 12

@rodrigograciano @CGuntur Watch for notes here How does Apache Maven work? (2) Internet Maven Repository Java (or other lang) Project Project Object Model (POM) assemble dependencies plugins profiles lifecycle build phases App Source Code Apache Maven 1 13 • Use Terminal or IDE • Navigate to the project root • List the phases (or phases:goals) • Run Apache Maven with above Notes

@rodrigograciano @CGuntur Watch for notes here How does Apache Maven work? (3) Internet Maven Repository Java (or other lang) Project Project Object Model (POM) assemble dependencies plugins profiles lifecycle build phases App Source Code Apache Maven assemble 1 2 • Maven parses the POM • Maven combines the below ... • Various settings • Maven defaults • POM overrides to defaults • … to produce an “effective POM” • Effective POM is read-only • It is the full set of what Maven uses Notes 14 effective POM

@rodrigograciano @CGuntur Watch for notes here How does Apache Maven work? (4) Internet Maven Repository {Local Repository (local cache) Java (or other lang) Project Project Object Model (POM) assemble dependencies plugins profiles lifecycle build phases App Source Code Apache Maven assemble 1 2 • If you previously ran a build • You may already have a local cache • Maven can use local cache • If you don’t have a local cache • Maven will use internet repository • Local cache will be created • Next run can depend on local cache Notes 15 effective POM

@rodrigograciano @CGuntur Watch for notes here How does Apache Maven work? (5) Internet Maven Repository {Local Repository (local cache) Java (or other lang) Project Project Object Model (POM) assemble dependencies plugins profiles lifecycle build phases App Source Code Apache Maven assemble 1 2 3 • Maven lists dependencies & plugins • Includes all defaults for non-configured • Creates a complete POM for building Notes 16 effective POM

@rodrigograciano @CGuntur Watch for notes here How does Apache Maven work? (6) Internet Maven Repository {Local Repository (local cache) Java (or other lang) Project Project Object Model (POM) assemble dependencies plugins profiles lifecycle build phases App Source Code Apache Maven assemble execute 1 2 4 • Maven executes phases or phases:goals • Profiles allow any or all of • alternate executions • alternate configurations • environment specificity Notes 17 effective POM 3

@rodrigograciano @CGuntur Watch for notes here How does Apache Maven work? (7) Internet Maven Repository {Local Repository (local cache) Java (or other lang) Project Project Object Model (POM) assemble dependencies plugins profiles lifecycle build phases App Source Code Apache Maven assemble 1 2 5 • Maven uses local cache if up-to-date • If not up-to-date (e.g. older SNAPSHOT) • Maven goes to non-local repository • Updates/adds to the cache • Next run can rely on local cache • Optional • Maven can push built “artifacts” • Artifacts can be pushed to: • local cache (local repository) • non-local repository Notes 18 execute 4 effective POM 3

@rodrigograciano @CGuntur How does Apache Maven work? (FINAL) {Local Repository (local cache) Java (or other lang) Project Project Object Model (POM) assemble dependencies plugins profiles lifecycle build phases App Source Code Apache Maven assemble 19 execute 4 2 1 Internet Maven Repository effective POM 3 5

@rodrigograciano @CGuntur Effective POM? 20

@rodrigograciano @CGuntur What is an “effective POM”? • an assembly of execution steps, properties and profiles • content that Maven can execute for the project • exhaustive set of dependencies and plugins that can be used to build • ready for execution by Maven executable 21

@rodrigograciano @CGuntur How is the effective POM created? Maven Internal Defaults Each lower block overrides previous values Maven Base POM Default POM (in maven jar, cannot override) Maven Global Settings Settings located under maven installation Maven User Settings Settings located under user home .m2 directory Parent/Bill-of-Material POM(s) Parent or BOM specified in project POM Maven Project POM The project POM Effective POM Read-only generated Effective POM 22

@rodrigograciano @CGuntur POM Hierarchies 23

@rodrigograciano @CGuntur POM Hierarchies Parent POM Another Parent POM Project POM Dependencies
 Plugins
 Properties Dependencies
 Plugins
 Properties Parentage Aggregation Aggregate POM Module 1 POM Module 2 POM Module 3 POM Module 4 POM No inheritance 
 of content Project knows Parent
 Parent does not know Project Parent can aggregate Project Module does not know Aggregator Module can set Aggregator as Parent
 Aggregator knows Module Bill-Of-Materials Bill-Of-Material POM Project 1 POM Project 2 POM Project 3 POM Project 4 POM Project inherits/imports Bill-Of-Materials
 Bill-Of-Materials does not know Project Bill-Of-Materials can aggregate Project Dependencies
 DependencyManagement 24

@rodrigograciano @CGuntur POM Hierarchies - example pom excerpts Parentage Aggregation Bill-Of-Materials Project knows Parent
 Parent can aggregate Project Module can set Aggregator as Parent
 Aggregator knows Module Project inherits/imports Bill-Of-Materials
 Bill-Of-Materials does not know Project 25

@rodrigograciano @CGuntur Maven 3.x … 26

@rodrigograciano @CGuntur Current state of Apache Maven 3 • Apache Maven is versatile, comprehensive and a great fit for corporations! • Some challenges exist: • Apache Maven 3: It is painful to maintain versions in multi-module projects • Apache Maven 3: Is no implicit way to separate build info from consumer info • Apache Maven 3: Handle versions of (dependency) sibling modules is a chore! • Apache Maven 3: We developers are lazy! We use default versions for plugins • Apache Maven 3: Creating a Bill-of-Materials POM is not easy! 
 27

@rodrigograciano @CGuntur Maintaining child module versions in Apache Maven 3 • No built-in support to propagate new version to child modules • Codehaus offers the flatten-maven-plugin • The flatten-maven-plugin has issues around profile interpolation • It requires including the third-party plugin
 
 https://maven.apache.org/maven-ci-friendly.html • Outbrain offers a ci-friendly-flatten-maven-plugin • This plugin solves the issue with profile interpolation • It requires including the third-party plugin
 
 https://github.com/outbrain/ci-friendly-flatten-maven-plugin • Both plugins use a revision property to set version values 28

@rodrigograciano @CGuntur Build info versus consumption info in Apache Maven 3 • POM contains build information - which is not relevant to a consumer! • Building an artifact produces a .pom file which contains irrelevant info • Once again both third party plugins come in handy: • Codehaus : flatten-maven-plugin • Outbrain : ci-friendly-flatten-maven-plugin 29

@rodrigograciano @CGuntur Versions of (dependency) sibling modules in Apache Maven 3 • Some multi-module projects have sibling dependencies • Managing versions of such can require using the project.version property • Limits testing to • either using most recent version of all siblings • or hardcoding versions during testing 30

@rodrigograciano @CGuntur Staying current on plugin versions in Apache Maven 3 • Apache Maven provides default versions of some plugins to use. • Best practice is to always set exact versions of plugins • In Apache Maven 3, there is no way to identify if a default version is in use. 31

@rodrigograciano @CGuntur Creating a Bill-of-Materials POM in Apache Maven 3 • Apache Maven has no “bom” packaging. 32

@rodrigograciano @CGuntur https://github.com/c-guntur/maven4 33 Let’s see some code! Maven 4.x …

@rodrigograciano @CGuntur Current state of Apache Maven 3 • Apache Maven is versatile, comprehensive and a great fit for corporations! • Some challenges exist: • Apache Maven 3: It is painful to maintain versions in multi-module projects
 Apache Maven 4: Version support is awesome! • Apache Maven 3: Is no implicit way to separate build info from consumer info
 Apache Maven 4: 2 separate POM files are generated! • Apache Maven 3: Handle versions of (dependency) sibling modules is a chore!
 Apache Maven 4: Implicit versions for (dependency) sibling modules • Apache Maven 3: We developers are lazy! We use default versions for plugins
 Apache Maven 4: Maven issues warnings when plugin versions are not declared • Apache Maven 3: Creating a Bill-of-Materials POM is not easy! 
 Apache Maven 4: Introduces the “bom” packaging option 34

@rodrigograciano @CGuntur There is a lot more … That’s all we have time for! 35 Questions?

@rodrigograciano @CGuntur Appendix 36

@rodrigograciano @CGuntur Maven POM Reference - project modelVersion parent groupId artifactId version name description url inceptionYear organization licenses developers contributors mailingLists scm issueManagement ciManagement distributionManagement repositories pluginRepositories modules properties build reporting profiles complex entity Legend simple entity expanded later dependencies dependencyManagement 37

@rodrigograciano @CGuntur Maven POM Reference - build sourceDirectory scriptSourceDirectory testSourceDirectory outputDirectory testOutputDirectory extensions testResources filters defaultGoal resources directory finalName complex entity Legend simple entity expanded later plugins pluginManagement 38

@rodrigograciano @CGuntur Maven POM Reference - [dependencyManagement/] dependencies/dependency complex entity Legend simple entity expanded later groupId artifactId version classifier type exclusions exclusion groupId artifactId scope systemPath optional 39

@rodrigograciano @CGuntur Maven POM Reference - [pluginManagement/] plugins/plugin complex entity Legend simple entity expanded later groupId artifactId version extensions inherited executions execution id phase inherited goals goal configuration dependencies configuration 40

@rodrigograciano @CGuntur Maven POM Reference - profiles/profile id activation testOutputDirectory distributionManagement modules repositories reporting dependencyManagement properties dependencies pluginRepositories complex entity Legend simple entity expanded later 41

@rodrigograciano @CGuntur Configuring Apache Maven JAVA_HOME Environment Variables .mvn Config Files jvm.config mvn.config XML Configurations /conf/settings.xml M2_HOME PATH MAVEN_OPTS /.m2/settings.xml /.mvn/extensions.xml /.m2/toolchains.xml /toolchains.xml 42

@rodrigograciano @CGuntur Understanding versioning strategies Development G:A:V-SNAPSHOT Testing, Bug Fixes
 
 Same Version Build, Continuous Integration
 
 Sharing during development Mutable Artifacts
 replaced every build Maven
 SNAPSHOT
 Repository Next Version
 
 Release Build, no SNAPSHOT
 
 Production-ready artifact Immutable Artifacts
 Should never be altered Maven
 RELEASE
 Repository Release G:A:V 1 2 3 4 43