Maven Structure

1
Maven Structure
2
POM The Project Object Model

• Defines structure of the project
• Supplies Metadata
• Has its own context where script variables and
  properties are loaded a form of scope
• basedir/project.properties and
  basedir/build.properties are loaded into the
  context, as well as defaults and
  /build.properties
• Both POM properties control build. General
  rule one plugin uses a property, but multiple
  plugins use POM elements

3
Dependencies and the Repository

• Dependencies can be of any type, but are
  typically JAR files
• Dependencies are downloaded from a remote
  repository (you can specify multiple), and placed
  in a local (per-user) repository
• If it is a JAR or EJB dependency, it is added to
  the classpath for build/execution
• Some dependencies have a special version SNAPSHOT

4
Goals

• Goals are like ant targets, but more flexible
  attainment tree
• All goals are defined in plug-ins, where prefix
  generally matches the plugin name.
• Eg. javacompile ? maven-java-plugin
• Goals can have prerequesites and hooks (preGoal
  and postGoal)

5
Plug-ins

• At the moment, plug-ins are all Jelly scripts
• Each contains goals and hooks that are run every
  time the goal is requested
• Conditionally enabled by presence of elements in
  the POM or variables/properties in the context
• Eg. JAXB plugin runs jaxbgenerate before
  javacompile every time. Only does anything if
• maven.jaxb.schemas is set
• Any of the above schemas have been changed since
  last build

6
Jelly Scripting

• XML scripting language that consists enitrely of
  tag libraries
• Sounds strange, but it is basically an
  implementation of JSP 2.0 and then some.
• Provides most of JSTL tags, and uses JEXL to do
  the expressions
• In maven, the default tag library is werkz
  which is used to define goals, but any others can
  be imported per script
• Maven.xml file in same directory as POM is a
  custom project jelly script

7
Jelly Scripting Example

• ltproject xmlnsantjellyant xmlnsjjellycore
  gt
• ltgoal namemy-new-goal prereqsmy-goalgt
• ltjif testmyPropertyyesgt
• ltantechogtmyProperty is yeslt/antechogt
• lt/jifgt
• lt/goalgt
• ltgoal namemy-goalgt
• ltjset varmyProperty valueyes/gt
• lt/goalgt
• ltpreGoal namejavacompilegt
• ltantechogtAbout to compilelt/antechogt
• lt/preGoalgt
• ltpostGoal namejavacompilegt
• ltantechogtFinished compilelt/antechogt
• lt/postGoalgt
• lt/projectgt

8
Maven Execution

• Checks all plugin JARs in MAVEN_HOME/plugins are
  unzipped to /.maven/cache
• Plugins are loaded from the unzipped plugins
  directory and goals are mapped. The scripts are
  actually executed, so any code outside of a goal
  is also run
• POM is loaded, with its properties
• Dependencies are checked for existence,
  downloaded if not in local repository. SNAPSHOT
  dependencies are downloaded again if the remote
  version is newer
• maven.xml parsed and run to define new goals
• Goals are found and executed

9
Reactor

• Reactor is used to run maven over multiple
  projects.
• Eg ltmavenreactor includesjava//project.xml
  goalsclean,site bannerRebuilding subproject
  site/gt
• Best used with the multiproject plugin

10
Multiproject

• Handles multiple different component types
• Can build an aggregated site and navigation
• Each project sets maven.multiproject.type
  property to jar, war, install, ear, etc.
• maven multiprojectinstall-snapshotmaven
  multiprojectdeploy-snapshot

11
Troubleshooting

• Read the build output see if you notice
  anything unusual (eg files copied/compiled not
  what you expected)
• Rebuild clean (rm rf target or maven clean will
  do the job)
• rm rf /.maven/cache
• Check for conflicting versions in
  MAVEN_HOME/plugins (global plugins) and
  HOME/.maven/plugins (user plugins)
• If you get an exception, run maven with e and
  report the trace to me or maven-user mailing
  list, or even better look in the maven source. It
  has a bad habit of throwing exceptions when there
  are reportable errors. File this in Maven's JIRA.
• If you get an error like /cache/maven-java-plugin
  -1.3.113111, look at plugin.jelly in the
  directory given at line 131, column 11. If it
  looks like a Maven bug, file in JIRA.
• Run maven X to get diagnostics during build
  (like ant debug). Eg outputs filtering
  replacements being made
• If you are having classpath/dependency problems
  check that the JARs in the local repository were
  downloaded correctly. Look for zero-length files
  in /.maven/repository. As a last resort, you can
  always rm rf /.maven/repository to get them
  again

12
Documentation

• Xdocs directory contains documentation for a
  project
• All .xml files are transformed to HTML
• Section, subsection, and tables treated specially
• Example next slide

13
Example Document

• ltdocumentgt
• ltpropertiesgt
• ltauthor emailbporter_at_f2network.com.augtBrett
  Porterlt/authorgt
• lttitlegtSome docolt/titlegt
• lt/propertiesgt
• ltbodygt
• ltsection nameDark blue headinggt
• ltpgtSome textlt/pgt
• ltsubsection nameLight gray headinggt
• ltpgtSome more textlt/pgt
• lt/subsectiongt
• ltsourcegtlt!CDATA
• example source code here
• gtlt/sourcegt
• lt/sectiongt
• lt/bodygt
• lt/documentgt