What is Maven?
Apache Maven is a software project management and comprehension tool. Based on the concept of a project object model (POM), Maven can manage a project's build, reporting and documentation from a central piece of information.
It is mainly for Java, but can also be used to build and manage projects written in C#, Ruby, Scala, and other languages.
Maven's primary goal is to allow a developer to comprehend the complete state of a development effort in the shortest period of time. In order to attain this goal there are several areas of concern that Maven attempts to deal with
- Making the build process easy
- Providing a uniform build system
- Providing quality project information
- Providing guidelines for best practices development
- Allowing transparent migration to new features
Linux, Solaris and Mac OS X
- Extract the distribution archive, i.e. apache-maven-3.0.4-bin.tar.gz to the directory you wish to install Maven 3.0.4. These instructions assume you chose /usr/local/apache-maven. The subdirectory apache-maven-3.0.4 will be created from the archive.
- In a command terminal, add the M2_HOME environment variable, e.g. export M2_HOME=/usr/local/apache-maven/apache-maven-3.0.4.
- Add the M2 environment variable, e.g. export M2=$M2_HOME/bin.
- Optional: Add the MAVEN_OPTS environment variable to specify JVM properties, e.g. export MAVEN_OPTS="-Xms256m -Xmx512m". This environment variable can be used to supply extra options to Maven.
- Add M2 environment variable to your path, e.g. export PATH=$M2:$PATH.
- Make sure that JAVA_HOME is set to the location of your JDK, e.g. export JAVA_HOME=/usr/java/jdk1.5.0_02 and that $JAVA_HOME/bin is in your PATH environment variable.
- Run mvn --version to verify that it is correctly installed.
Maven has a settings file located in the Maven installation and/or user home directory that configure environmental specifics such as
- HTTP proxy server
- repository manager location
- server authentication and passwords
- other configuration properties
For information on this file, see the Settings reference
Set environment variables
Run mvn --version
Creating a project
You will need somewhere for your project to reside, create a directory somewhere and start a shell in that directory. On your command line, execute the following Maven goal.
The command executed the Maven goal archetype:generate, and passed in various parameters to that goal. The prefix archetype is the plugin that contains the goal. If you are familiar with Ant, you may conceive of this as similar to a task. This goal created a simple project based upon an archetype. Suffice it to say for now that a plugin is a collection of goals with a general common purpose. For example the jboss-maven-plugin, whose purpose is "deal with various jboss items".
NOTE: If you have just installed Maven, it may take a while on the first run. This is because Maven is downloading the most recent artifacts (plugin jars and other files) into your local repository. You may also need to execute the command a couple of times before it succeeds. This is because the remote server may time out before your downloads are complete. Don't worry, there are ways to fix that.
Create project interactively
Once finished, you will notice that the generate goal created a directory with the same name given as the artifactId. Change into that directory.
The src/main/java directory contains the project source code, the src/test/java directory contains the test source, and the pom.xml file is the project's Project Object Model, or POM.
The pom.xml file is the core of a project's configuration in Maven. It is a single configuration file that contains the majority of information required to build a project in just the way you want. The POM is huge and can be daunting in its complexity, but it is not necessary to understand all of the intricacies just yet to use it effectively. This project's POM is
Build The Project
Unlike the first command executed (archetype:generate) you may notice the second is simply a single word - package. Rather than a goal, this is a phase. A phase is a step in the build lifecycle, which is an ordered sequence of phases. When a phase is given, Maven will execute every phase in the sequence up to and including the one defined.
For example, if we execute the compile phase, the phases that actually get executed are:
clean- remove all files generated by the previous build
Running Maven Tools
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
Phases are actually mapped to underlying goals. The specific goals executed per phase is dependant upon the packaging type of the project. For example, package executes jar:jar if the project type is a JAR, and war:war is the project type is - you guessed it - a WAR.
An interesting thing to note is that phases and goals may be executed in sequence.
This command will clean the project, copy dependencies, and package the project (executing all phases up to package, of course).
Generates the project's site documentation