Post#81.Maven Build Life Cycles, Phases and Goals

Maven Build Life Cycles, Phases and Goals

When Maven builds a software project it follows a build life cycle. The build life cycle is divided into build phases, and the build phases are divided into build goals. 

*Detailed in the Maven Introduction to Build Life Cycles.

Build Life Cycles
Maven has 3 built-in build life cycles. These are:

1. default
2. clean
3. site

Each of these build life cycles takes care of a different aspect of building a software project. Thus, each of these build life cycles are executed independently of each other. You can get Maven to execute more than one build life cycle, but they will be executed in sequence, separately from each other.

The default life cycle handles everything related to compiling and packaging your project.

The clean life cycle handles everything related to removing temporary files from the output directory, including generated source files, compiled classes, previous JAR files etc.

The site life cycle handles everything related to generating documentation for your project. In fact, site can generate a complete website with documentation for your project.

Build Phases
Each build life cycle is divided into a sequence of build phases, and the build phases are again subdivided into goals. Thus, the total build process is a sequence of build life cycle(s), build phases and goals.

You can execute either a whole build life cycle like clean or site, a build phase like install which is part of the default build life cycle, or a build goal like dependency:copy-dependencies. Note: You cannot execute the default life cycle directly. You have to specify a build phase or goal inside the default life cycle.

When you execute a build phase, all build phases before that build phase in this standard phase sequence are executed. Thus, executing the install build phase really means executing all build phases before the install phase, and then execute the install phase after that.

The default life cycle is of most interest since that is what builds the code. Since you cannot execute the default life cycle directly, you need to execute a build phase or goal from the default life cycle. The default life cycle has an extensive sequence of build phases and goals, ,so I will not describe them all here. The most commonly used build phases are:

Build Phase	Description
validate	Validates that the project is correct and all necessary information is available. This also makes sure the dependencies are downloaded.
compile	Compiles the source code of the project.
test	Runs the tests against the compiled source code using a suitable unit testing framework. These tests should not require the code be packaged or deployed.
package	Packs the compiled code in its distributable format, such as a JAR.
install	Install the package into the local repository, for use as a dependency in other projects locally.
deploy	Copies the final package to the remote repository for sharing with other developers and projects.

You execute one of these build phases by passing its name to the mvn command. 

Here is an example:

mvn package

This example executes the package build phase, and thus also all build phases before it in Maven's predefined build phase sequence.

If the standard Maven build phases and goals are not enough to build your project, you can create Maven plugins to add the extra build functionality you need.

Build Goals
Build goals are the finest steps in the Maven build process. A goal can be bound to one or more build phases, or to none at all. If a goal is not bound to any build phase, you can only execute it by passing the goals name to the mvn command. If a goal is bound to multiple build phases, that goal will get executed during each of the build phases it is bound to.