What is Maven?
Maven is a powerful project/build management tool that is
based on POM (project object model).
What is a Build Tool?
A build tool is a tool that automates everything related to
building the software project. Building a software project typically includes
one or more of these activities:
- Generating
source code (if auto-generated code is used in the project).
- Generating
documentation from the source code.
- Compiling
source code.
- Packaging
compiled code into JAR files or ZIP files.
- Installing
the packaged code on a server, in a repository or somewhere else.
Any given software project may have more activities than
these needed to build the finished software. Such activities can normally be
plugged into a build tool, so these activities can be automated too.
The advantage of automating the build process is that you
minimize the risk of humans making errors while building the software manually.
Additionally, an automated build tool is typically faster than a human
performing the same steps manually.
Maven Overview - Core Concepts
Maven
is centered on the concept of POM files (Project Object Model). A POM file is
an XML representation of project resources like source code, test code,
dependencies (external JARs used) etc. The POM contains references to all of
these resources. The POM file should be located in the root directory of the
project it belongs to.
Here
is a diagram illustrating how Maven uses the POM file, and what the POM file
primarily contains:
Overview of Maven-core concepts.
These concepts are
explained briefly below to give you an overview, and then in more detail in
their own sections later
POM Files
When you execute a Maven command you give Maven a POM file to execute the commands on. Maven will then execute the command on the resources described in the POM.
When you execute a Maven command you give Maven a POM file to execute the commands on. Maven will then execute the command on the resources described in the POM.
Build Life Cycles, Phases and Goals
The build process in Maven is split up into build life cycles, phases and goals. A build life cycle consists of a sequence of build phases, and each build phase consists of a sequence of goals. When you run Maven you pass a command to Maven. This command is the name of a build life cycle, phase or goal. If a life cycle is requested executed, all build phases in that life cycle are executed. If a build phase is requested executed, all build phases before it in the pre-defined sequence of build phases are executed too.
The build process in Maven is split up into build life cycles, phases and goals. A build life cycle consists of a sequence of build phases, and each build phase consists of a sequence of goals. When you run Maven you pass a command to Maven. This command is the name of a build life cycle, phase or goal. If a life cycle is requested executed, all build phases in that life cycle are executed. If a build phase is requested executed, all build phases before it in the pre-defined sequence of build phases are executed too.
Dependencies and
Repositories
One of the first goals Maven executes is to check the dependencies needed by your project. Dependencies are external JAR files (Java libraries) that your project uses. If the dependencies are not found in the local Maven repository, Maven downloads them from a central Maven repository and puts them in your local repository. The local repository is just a directory on your computer's hard disk. You can specify where the local repository should be located if you want to (I do). You can also specify which remote repository to use for downloading dependencies. All this will be explained in more detail later.
One of the first goals Maven executes is to check the dependencies needed by your project. Dependencies are external JAR files (Java libraries) that your project uses. If the dependencies are not found in the local Maven repository, Maven downloads them from a central Maven repository and puts them in your local repository. The local repository is just a directory on your computer's hard disk. You can specify where the local repository should be located if you want to (I do). You can also specify which remote repository to use for downloading dependencies. All this will be explained in more detail later.
Build Plugins
Build plugins are used to insert extra goals into a build phase. If you need to perform a set of actions for your project which are not covered by the standard Maven build phases and goals, you can add a plugin to the POM file. Maven has some standard plugins you can use, and you can also implement your own in Java if you need to.
Build plugins are used to insert extra goals into a build phase. If you need to perform a set of actions for your project which are not covered by the standard Maven build phases and goals, you can add a plugin to the POM file. Maven has some standard plugins you can use, and you can also implement your own in Java if you need to.
Build Profiles
Build profiles are used if you need to build your project in different ways. For instance, you may need to build your project for your local computer, for development and test. And you may need to build it for deployment on your production environment. These two builds may be different. To enable different builds you can add different build profiles to your POM files. When executing Maven you can tell which build profile to use.
Build profiles are used if you need to build your project in different ways. For instance, you may need to build your project for your local computer, for development and test. And you may need to build it for deployment on your production environment. These two builds may be different. To enable different builds you can add different build profiles to your POM files. When executing Maven you can tell which build profile to use.
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