@CGuntur https://cguntur.me Apache Maven A Peek Under The Hood Chandra Guntur Oct. 2023 1

https://cguntur.me @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

https://cguntur.me @CGuntur What is “build management”? • compiling - compile code • packaging executables - create a .jar, .war, .zip etc. • testing - unit/functional/integration testing can be orchestrated • generating documentation - javadoc/site generation capabilities • generating metrics/reports - build metrics, test result reports • deploying - push to repository or to server 3

https://cguntur.me @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 4

@CGuntur https://cguntur.me What is a POM? 5

https://cguntur.me @CGuntur “POM” is … A Pomeranian? Pomegranate Juice? One of the Pom-poms? 6

https://cguntur.me @CGuntur • POM lists: • dependencies • plugins • properties • inheritance details • profiles • ... “POM” is … A Pomeranian? Pomegranate Juice? One of the Pom-poms? 7 POM is Project Object Model

https://cguntur.me @CGuntur “POM” is … Appendix has POM structure details … 8

@CGuntur https://cguntur.me Benefits/usage of Apache Maven? 9

https://cguntur.me @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 10

https://cguntur.me @CGuntur Apache Maven usage • create any auto-generated source code, if needed • generate documentation from source code • compile source code, display any errors and warnings • test the project running existing tests in source code • package compiled code into a .jar or .war or .zip etc. • additionally, package source code into a .jar or .zip • install the packaged code into a repository/server • generate site reports and test evidence • in addition to reporting a build as success or failure 11

@CGuntur https://cguntur.me How does Apache Maven work? 12

https://cguntur.me @CGuntur Watch for notes here How does Apache Maven work? 13 Java (or other lang) Project App Source Code Internet Maven Repository

https://cguntur.me @CGuntur How does Apache Maven work? (1) 14 Java (or other lang) Project App Source Code Project Object Model (POM) assemble dependencies plugins profiles lifecycle build phases Watch for notes here • Add a pom (typically a pom.xml file) • Point settings.xml to repository • Include dependencies & plugins • Add properties & override configuration Notes Internet Maven Repository

https://cguntur.me @CGuntur How does Apache Maven work? (2) 15 Java (or other lang) Project App Source Code Project Object Model (POM) assemble dependencies plugins profiles lifecycle build phases Watch for notes here • Use Terminal or IDE • Navigate to the project root • List the phases (or phases:goals) • Run Apache Maven with above Notes Apache Maven 1 Internet Maven Repository

https://cguntur.me @CGuntur How does Apache Maven work? (3) 16 Java (or other lang) Project App Source Code Project Object Model (POM) dependencies plugins profiles lifecycle build phases assemble Watch for notes here • 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 1 Apache Maven assemble 2 effective POM Internet Maven Repository

https://cguntur.me @CGuntur How does Apache Maven work? (4) 17 Java (or other lang) Project App Source Code Internet Maven Repository Project Object Model (POM) dependencies plugins profiles lifecycle build phases assemble Watch for notes here • 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 1 Apache Maven assemble 2 effective POM {Local Repository (local cache)

https://cguntur.me @CGuntur How does Apache Maven work? (5) 18 Java (or other lang) Project App Source Code Internet Maven Repository Project Object Model (POM) dependencies plugins profiles lifecycle build phases assemble Watch for notes here • Maven fetches dependencies & plugins • Transitive dependencies are also fetched • 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 Notes 1 Apache Maven assemble 2 effective POM {Local Repository (local cache) 3

https://cguntur.me @CGuntur How does Apache Maven work? (6) 19 Java (or other lang) Project App Source Code Internet Maven Repository Project Object Model (POM) profiles lifecycle build phases assemble dependencies plugins Watch for notes here • Maven executes phases or phases:goals • Profiles allow any or all of • alternate executions • alternate configurations • environment specificity Notes 1 Apache Maven assemble 2 effective POM {Local Repository (local cache) 3 execute 4

https://cguntur.me @CGuntur How does Apache Maven work? (7) 20 Java (or other lang) Project App Source Code Internet Maven Repository Project Object Model (POM) profiles lifecycle build phases assemble dependencies plugins Watch for notes here • Optional • Maven can push built “artifacts” • Artifacts can be pushed to: • local cache (local repository) • non-local repository Notes 1 Apache Maven assemble 2 effective POM {Local Repository (local cache) 3 execute 4 5

https://cguntur.me @CGuntur { Java (or other lang) Project Project Object Model (POM) assemble dependencies plugins profiles lifecycle build phases App Source Code Apache Maven assemble 21 execute 5 4 3 2 1 effective POM How does Apache Maven work? (FINAL) Internet Maven Repository Local Repository (local cache)

@CGuntur https://cguntur.me Effective POM? 22

https://cguntur.me @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 • lists all dependencies and their transitive dependencies • any potential dependency conflict resolution • ready for execution by Maven executable 23

https://cguntur.me @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 24

@CGuntur https://cguntur.me POM Hierarchies 25

https://cguntur.me @CGuntur POM Hierarchies Parent POM Another Parent POM Project POM Dependencies
 Plugins
 Properties Dependencies
 Plugins
 Properties Parentage Aggregation 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 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
 Plugins
 Properties 26 Aggregate POM Bill-Of-Material POM

https://cguntur.me @CGuntur Project inherits/imports Bill-Of-Materials
 Bill-Of-Materials does not know Project Bill-Of-Materials can aggregate Project 27 Project knows Parent
 Parent can aggregate Project Module can set Aggregator as Parent
 Aggregator knows Module POM Hierarchies - example pom excerpts Parentage Aggregation Bill-Of-Materials

@CGuntur https://cguntur.me Under the hood 28

https://cguntur.me @CGuntur Lifecycles in Maven Standard Lifecycles 
 validate initialize generate-sources process-sources generate-resources process-resources compile process-classes generate-test-sources process-test-sources generate-test-resources process-test-resources 
 test-compile process-test-classes test prepare-package package pre-integration-test integration-test post-integration-test verify install deploy
 build (default) Phases 
 pre-clean
 clean
 post-clean Phases 
 pre-site
 site
 post-site site-deploy Phases 29 clean site

https://cguntur.me @CGuntur Lifecycles in Maven - default phases Standard Lifecycles 
 validate initialize generate-sources process-sources generate-resources process-resources compile process-classes generate-test-sources process-test-sources generate-test-resources process-test-resources 
 test-compile process-test-classes test prepare-package package pre-integration-test integration-test post-integration-test verify install deploy
 build (default) Phases 
 pre-clean
 clean
 post-clean Phases 
 pre-site
 site
 post-site site-deploy Phases 30 clean site default phase Legend

https://cguntur.me @CGuntur Lifecycles in Maven - common phases used Standard Lifecycles 
 validate initialize generate-sources process-sources generate-resources process-resources compile process-classes generate-test-sources process-test-sources generate-test-resources process-test-resources 
 test-compile process-test-classes test prepare-package package pre-integration-test integration-test post-integration-test verify install deploy
 build (default) Phases 
 pre-clean
 clean
 post-clean Phases 
 pre-site
 site
 post-site site-deploy Phases 31 clean site Legend not commonly invoked commonly invoked

https://cguntur.me @CGuntur Lifecycles in Maven - calling “mvn clean compile” Standard Lifecycles 
 validate initialize generate-sources process-sources generate-resources process-resources compile process-classes generate-test-sources process-test-sources generate-test-resources process-test-resources 
 test-compile process-test-classes test prepare-package package pre-integration-test integration-test post-integration-test verify install deploy
 build (default) Phases 
 pre-clean
 clean
 post-clean Phases 
 pre-site
 site
 post-site site-deploy Phases 32 clean site

https://cguntur.me @CGuntur Lifecycles: Under the hood • command: mvn clean compile • first calls clean:clean (default phase of clean lifecycle is clean): pre-clean clean • then invokes the following phases of default lifecycle (no prefix): validate initialize generate-sources process-sources generate-resources process-resources compile 33

https://cguntur.me @CGuntur Plugins Plugins Goal name4 Plugin 2 . . . Plugin 1 Goal name1 Lifecycle phase 1
 
 phase 2 
 phase 3 Plugin 3 Goal name2 phase 1 Goal name5 phase 1 Goal name3 phase 3 Lifecycle 34

https://cguntur.me @CGuntur Plugins: Under the hood • a lifecycle phase by itself does not perform any task • tasks are performed by plugins • plugins allow phases to carry out responsibilities • plugins declare goals • a plugin goal defines a specific task towards building/managing the project • a plugin goal may be bound to zero or more lifecycle phases • invoking a phase invokes plugin goals linked to the phase • in addition to calling lifecycles or their phases, possible to invoke a plugin goal • default bindings of lifecycle phase to plugin goal may depend on packaging • package phase for ejb will call ejb goal from the maven-ejb-plugin • package phase for jar will call jar goal from the maven-jar-plugin • generate-resources phase for ear will call generate-application-xml goal from the maven-ear-plugin 35

https://cguntur.me @CGuntur Dependencies - graph Exclusions Dependency G-A-V Scope Type Dependency G-A-V Scope Type Dependency G-A-V Scope Type Dependency G-A-V Scope Type Dependency G-A-V Scope Type Dependency G-A-V Scope Type Dependency G-A-V Scope Type Dependency G-A-V Scope Type Dependency G-A-V Scope Type Dependency G-A-V Scope Type Optional Exclusions 1 2 3 4 5 36 Optional

https://cguntur.me @CGuntur Dependencies - resolution ??? Dependency Graph Dependency D1 G1:A1:V1 Dependency D11 G11:A11:V11 Dependency D311 G34:A34:V34 Dependency Dx Gx:Ax:V1.0.0 Dependency Dx Gx:Ax:V1.2.0 Dependency D31 G33:A33:V33 Dependency Dx Gx:Ax:V1.3.0 Dependency Dx Gx:Ax:V1.5.0 Dependency D2 G2:A2:V2 Dependency D3 G3:A3:V3 Dependency D4 G4:A4:V4 Selection ? Dx v1.2.0 ? Dx v1.3.0 ? Dx v1.5.0 ? Dx v1.0.0 ?

https://cguntur.me @CGuntur Dependencies - resolution !!! Dependency Graph Dependency D1 G1:A1:V1 Dependency D11 G11:A11:V11 Dependency D311 G34:A34:V34 Dependency Dx Gx:Ax:V1.0.0 Dependency Dx Gx:Ax:V1.2.0 Dependency D31 G33:A33:V33 Dependency Dx Gx:Ax:V1.3.0 Dependency Dx Gx:Ax:V1.5.0 Dependency D2 G2:A2:V2 Dependency D3 G3:A3:V3 Dependency D4 G4:A4:V4 Selection ? Selected v1.2.0
 Nearest in depth First in resolution path Omitted v1.3.0
 Not nearest in depth Omitted v1.5.0
 Not first in resolution path Omitted v1.0.0
 Not nearest in depth

@CGuntur https://cguntur.me Questions? There is a lot more … That’s all we have time for! 39

@CGuntur https://cguntur.me Appendix 40

https://cguntur.me @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 dependencies dependencyManagement 41 Legend complex entity simple entity expanded later

https://cguntur.me @CGuntur Maven POM Reference - build sourceDirectory scriptSourceDirectory testSourceDirectory outputDirectory testOutputDirectory extensions testResources filters defaultGoal resources directory finalName plugins pluginManagement 42 Legend complex entity simple entity expanded later

https://cguntur.me @CGuntur Maven POM Reference - [dependencyManagement/] dependencies/dependency groupId artifactId version classifier type exclusions exclusion groupId artifactId scope systemPath optional 43 Legend complex entity simple entity expanded later

https://cguntur.me @CGuntur Maven POM Reference - [pluginManagement/] plugins/plugin groupId artifactId version extensions inherited executions execution id phase inherited goals goal configuration configuration 44 dependencies Legend complex entity simple entity expanded later

https://cguntur.me @CGuntur Maven POM Reference - profiles/profile id activation testOutputDirectory distributionManagement modules repositories reporting properties pluginRepositories 45 dependencies dependencyManagement Legend complex entity simple entity expanded later

https://cguntur.me @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 46

https://cguntur.me @CGuntur Testing, Bug Fixes
 
 Same Version 1 Understanding versioning strategies Development G:A:V-SNAPSHOT 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 2 3 4 47