Maven Introduction and Concepts (Part – I)
Background
I am using Maven for build and release management for last 4years or so. But recently when I started using ‘Flex Mojos’ plug-in for building my Flex project I realized that I do not have some of the basic knowledge about the Maven. I have to admit that I had only 30-40% of knowledge. For last few days I started reading “Maven – The Definitive Guide” from Sonatype and thought I will share some of the core concepts. I am planning to split this in to 2 parts. In first part I will cover core concepts about the Maven and in 2nd part I will cover different useful plug-ins and important commands.
Audience
This article assumes that you have some working knowledge of Maven2 and this should be used as a reference only.
Core Concepts
The core of Maven is pretty dumb, it doesn’t know how to do much beyond parsing few XML documents and keeping track of few lifecycle and few plugins. Most of the stuff is delegated to plugins.
Convention over Configuration
Systems, libraries, and frameworks should assume reasonable defaults. Without requiring unnecessary configuration, systems should “just work”. Popular frameworks “Ruby On Rails” and EJB3 are based on this concept.
I have seen people breaking this rule and saying Maven is “stupid” it assumes my source files in “src\main\java” directory and I do not want to adhere to this folder structure. That is fine you can use whatever the structure you want and Maven doesn’t put any restriction on this but in your POM, make sure you tell that to Maven. But think again when you break any of these rules. I would do this only if somebody else owns this project and is a legacy code.
Plugins and Goals
A Maven plugin is a collection of one or more goals.
A goal is a “unit of work”. It is a specific task that may be executed as standalone goal or along with other goals as part of larger build.
mvn archetype:create (pluginId:goalId)
Maven Lifecycle
The build lifecycle is an ordered sequence of phases involved in building a project. Most often used is the default Maven lifecycle, which begins with a phase to validate the basic integrity of the project and ends with a phase that involves deploying a project to production.
Plugin goals can be attached to a lifecycle phase. As Maven moves through the phases in a lifecycle, it will execute the goals attached to each particular phase. Each phase may have zero or more goals bound to it.
mvn install (install – It is one of lifecycle phase)
Maven Co-ordinates
Maven Coordinates define a set of identifiers which can be used to uniquely identify a project, a dependency, or a plugin in a Maven POM
Maven Repositories
When you run Maven for the first time, you will notice that Maven downloads a number of files from a remote Maven repository. Maven ships with the bare minimum and fetches from a remote repository when it needs to. Maven ships with a default remote repository location (http://repo1.maven.org/maven2)
Maven Dependency (Transitive Dependency)
A dependency in Maven isn’t just a JAR file; it’s a POM file that, in turn, may declare dependencies on other artifacts. These dependencies of dependencies are called transitive dependencies
Optimizing Dependencies
In a multi module project use “dependencyManagement” section to categorize all the common dependency jar’s between projects. This avoids dependency duplication and sibling dependency mis-match.
<project> ….. <dependencyManagement> <dependencies> <dependency> <groupId>org.springframework</groupId> <artifactId>spring</artifactId> <version>2.0.7</version> </dependency> <dependencies> <dependencyManagement> </project>
Optimizing Plugins
Use “pluginManagement” section in top level POM just like the way we use for Dependency management.
<project> ….. <build> <pluginManagement> <plugins> <plugin> <groupId> org.apache.maven.plugins </groupId> <artifactId>maven-complier-plugin</artifactId> <configuration> <source>1.5</source> <target>1.5</target> </configuration> </plugin> </plugins> < pluginManagement > </build> </project>
