Maven

Maven is a dependency management system and build tool for rapid Java-based application development with rich features to streamline development and SCM. Maven is a Yiddish word which means "accumulator of knowledge". The Maven Project started out as an attempt to simplify build processes in a project with multiple Ant build scripts. It was proposed that a standard way to build projects, clearly define what a project consists of, easily publish project information and share JARs across several different projects would greatly simplify and lend efficiency and speed to the Java development process.

Phases

Although hardly a comprehensive list, these are the most common default lifecycle phases executed.

validate - validate the project is correct and all necessary information is available
compile - compile the source code of the project
test - test the compiled source code using a suitable unit testing framework. These tests should not require the code be packaged or deployed
package - take the compiled code and package it in its distributable format, such as a JAR.
integration-test - process and deploy the package if necessary into an environment where integration tests can be run
verify - run any checks to verify the package is valid and meets quality criteria
install - install the package into the local repository, for use as a dependency in other projects locally
deploy - done in an integration or release environment, copies the final package to the remote repository for sharing with other developers and projects.

There are two other Maven lifecycles of note beyond the default list above. They are

clean - cleans up artifacts created by prior builds
site - generates site documentation for this project

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Build Commands

The following are some useful commands (don't forget to remove "mvn" before adding a command to a Run Configuration in your IDE of choice, the plugin will automatically call Maven).

Standard full clean & install (with complete maven repository building of dependencies via POM dependency list):

mvn clean install -PautoInstallPackage

Clean the target directory, build and explode out a WAR file, run it in an embedded Jetty server (should be configured properly in pom.xml).

mvn clean war:exploded jetty:run -e

Run unit tests:

mvn test

Package a runnable JAR, WAR or EAR:

mvn package

Build a new snapshot and release:

mvn -U deploy

An interesting thing to note is that phases and goals may be executed in sequence:

mvn clean dependency:copy-dependencies package

Troubleshooting

Search for JARs in your local Maven repository (local cache):

file ~/.m2/repository/org/jsoup/jsoup/1.10.3/jsoup-1.10.3.jar

Given a specific JAR, search contents to find a specific class (for debugging any "ClassNotFoundException" and similar issues):

jar -tf ~/.m2/repository/org/jsoup/jsoup/1.10.3/jsoup-1.10.3.jar | grep org/jsoup/parser/Parser

POM

In Maven, the Project Object Model (POM) is the term given to the XML-based definition of a project (similar to DOAP), which focuses on providing a listing of Dependencies (libraries, supporting tools, etc), where to download or obtain those Dependencies, and how to use those dependencies together with the code contained in the software project in order to successfully perform a Build. It also provides a linkage to Defect Management (aka. Issue Management) & Testing tools. The following is an empty template for the syntax of the POM file.

 <project xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
                      http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <!-- The Basics -->
  <groupId>...</groupId>
  <artifactId>...</artifactId>
  <version>...</version>
  <packaging>...</packaging>
   <dependencies>
     <dependency>
       <groupId>...</groupId>
       <artifactId>...</artifactId>
       <version>...</version>
     </dependency>
   </dependencies>
   <parent>...</parent>
   <dependencyManagement>...</dependencyManagement>
   <modules>...</modules>
   <properties>...</properties>

  <!-- Build Settings -->
   <build>...</build>
   <reporting>...</reporting>

  <!-- Additional Project Information -->
   <name>...</name>
   <description>...</description>
   <url>...</url>
   <inceptionYear>...</inceptionYear>
   <licenses>...</licenses>
   <organization>...</organization>
   <developers>...</developers>
   <contributors>...</contributors>

   <!-- Environment Settings -->
   <issueManagement>...</issueManagement>
   <ciManagement>...</ciManagement>
   <mailingLists>...</mailingLists>
   <scm>...</scm>
   <prerequisites>...</prerequisites>
   <repositories>...</repositories>
   <pluginRepositories>...</pluginRepositories>
   <distributionManagement>...</distributionManagement>
   <profiles>...</profiles>
 </project>

Tools

Apache Maven: http://maven.apache.org
Maven Version Manager: http://mvnvm.org (enables use of different Maven versions per project)

Plugins

Releases

Releases Maven plugin: http://maven.apache.org/maven-release/maven-release-plugin/ (manage the release number of your project's build artifacts)

Versions

Versions Maven plugin: http://www.mojohaus.org/versions-maven-plugin/ (manage the versions of artifacts in a project's POM, external dependencies, etc)

SCM

SCM Maven plugin: https://maven.apache.org/scm/maven-scm-plugin/index.html (connect to local or remote repos such as GIT or SVN and can grab specific commits, tags, etc)

Properties

Properties Maven plugin: http://www.mojohaus.org/properties-maven-plugin/index.html (set custom properties, system properties, environment variables, etc... and pass them into other commands or build goals)

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Exec

Exec Maven plugin: http://www.mojohaus.org/exec-maven-plugin/index.html | DOCS (run command-line commands in a separate and/or parallel process)

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Continuous Integration

Doing a release on Hudson using Maven 2 (OLD way, without plugin, from Hudson front-end): http://www.manorrock.com/documents/hudson/maven-release.html

Static Code Analysis

Config processor

maven-config-processor-plugin -- Configuration Processor Plugin for Maven: http://code.google.com/p/maven-config-processor-plugin/

Castor

Generating Java source code from a single XML schema: http://mojo.codehaus.org/castor-maven-plugin/example-simple.html

Exec (command-line)

maven-exec-plugin: http://mojo.codehaus.org/exec-maven-plugin/ (execute any program that can be run from the command-line)

CloudTools

cloudtools : http://code.google.com/p/cloudtools/wiki/UsingTheCloudToolsMavenPlugin

Language Extensions

While just about any program can be run remotely in a cloud environment via the CloudTools plugin, or by calling a local program from the command-line via the Exec plugin, there are still instances when you want to work more closely with a given programming language's specific tools such as compilers, testing suites, IDEs, etc. You can accomplish this by using one of the many Language-specific Maven extensions.