Introduction to the Build Lifecycle

Table Of Contents

• Build Lifecycle Basics
• Setting Up Your Project to Use the Build Lifecycle
  • Packaging
  • Plugins
• Lifecycle Reference
• Built-in Lifecycle Bindings

Build Lifecycle Basics

Maven is based around the central concept of a build lifecycle. What this means is that the process for building and distributing a particular artifact (project) is clearly defined.

For the person building a project, this means that it is only necessary to learn a small set of commands to build any Maven project, and the POM will ensure they get the results they desired.

There are three built-in build lifecycles: default, clean and site. The default lifecycle handles your project deployment, the clean lifecycle handles project cleaning, while the site lifecycle handles the creation of your project's site documentation.

A Build Lifecycle is Made Up of Phases

Each of these build lifecycles is defined by a different list of build phases, wherein a build phase represents a stage in the lifecycle.

For example, the default lifecycle comprises of the following phases (for a complete list of the lifecycle phases, refer to the Lifecycle Reference):

• 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.
• verify - run any checks on results of integration tests to ensure quality criteria are met
• install - install the package into the local repository, for use as a dependency in other projects locally
• deploy - done in the build environment, copies the final package to the remote repository for sharing with other developers and projects.

These lifecycle phases (plus the other lifecycle phases not shown here) are executed sequentially to complete the default lifecycle. Given the lifecycle phases above, this means that when the default lifecycle is used, Maven will first validate the project, then will try to compile the sources, run those against the tests, package the binaries (e.g. jar), run integration tests against that package, verify the integration tests, install the verified package to the local repository, then deploy the installed package to a remote repository.

[top].

Usual Command Line Calls

You should select the phase that matches your outcome. If you want your jar, run package. If you want to run the unit tests, run test.

If you are uncertain what you want, the preferred phase to call is

mvn verify

This command executes each default lifecycle phase in order (validate, compile, package, etc.), before executing verify. You only need to call the last build phase to be executed, in this case, verify. In most cases the effect is the same as package. However, in case there are integration-tests, these will be executed as well. And during the verify phase some additional checks can be done, e.g. if your code written according to the predefined checkstyle rules.

In a build environment, use the following call to cleanly build and deploy artifacts into the shared repository.

mvn clean deploy

The same command can be used in a multi-module scenario (i.e. a project with one or more subprojects). Maven traverses into every subproject and executes clean, then executes deploy (including all of the prior build phase steps).

[top].

A Build Phase is Made Up of Plugin Goals

However, even though a build phase is responsible for a specific step in the build lifecycle, the manner in which it carries out those responsibilities may vary. And this is done by declaring the plugin goals bound to those build phases.

A plugin goal represents a specific task (finer than a build phase) which contributes to the building and managing of a project. It may be bound to zero or more build phases. A goal not bound to any build phase could be executed outside of the build lifecycle by direct invocation. The order of execution depends on the order in which the goal(s) and the build phase(s) are invoked. For example, consider the command below. The clean and package arguments are build phases, while the dependency:copy-dependencies is a goal (of a plugin).

mvn clean dependency:copy-dependencies package

If this were to be executed, the clean phase will be executed first (meaning it will run all preceding phases of the clean lifecycle, plus the clean phase itself), and then the dependency:copy-dependencies goal, before finally executing the package phase (and all its preceding build phases of the default lifecycle).

Moreover, if a goal is bound to one or more build phases, that goal will be called in all those phases.

Furthermore, a build phase can also have zero or more goals bound to it. If a build phase has no goals bound to it, that build phase will not execute. But if it has one or more goals bound to it, it will execute all those goals.

(Note: In Maven 2.0.5 and above, multiple goals bound to a phase are executed in the same order as they are declared in the POM, however multiple instances of the same plugin are not supported. Multiple instances of the same plugin are grouped to execute together and ordered in Maven 2.0.11 and above).

[top].

Some Phases Are Not Usually Called From the Command Line

The phases named with hyphenated-words (pre-*, post-*, or process-*) are not usually directly called from the command line. These phases sequence the build, producing intermediate results that are not useful outside the build. In the case of invoking integration-test, the environment may be left in a hanging state.

Code coverage tools such as Jacoco and execution container plugins such as Tomcat, Cargo, and Docker bind goals to the pre-integration-test phase to prepare the integration test container environment. These plugins also bind goals to the post-integration-test phase to collect coverage statistics or decommission the integration test container.

Failsafe and code coverage plugins bind goals to integration-test and verify phases. The net result is test and coverage reports are available after the verify phase. If integration-test were to be called from the command line, no reports are generated. Worse is that the integration test container environment is left in a hanging state; the Tomcat webserver or Docker instance is left running, and Maven may not even terminate by itself.

[top].

Setting Up Your Project to Use the Build Lifecycle

The build lifecycle is simple enough to use, but when you are constructing a Maven build for a project, how do you go about assigning tasks to each of those build phases?

Packaging

The first, and most common way, is to set the packaging for your project via the equally named POM element <packaging>. Some of the valid packaging values are jar, war, ear and pom. If no packaging value has been specified, it will default to jar.

Each packaging contains a list of goals to bind to a particular phase. For example, the jar packaging will bind the following goals to build phases of the default lifecycle.

Phase	plugin:goal
process-resources	resources:resources
compile	compiler:compile
process-test-resources	resources:testResources
test-compile	compiler:testCompile
test	surefire:test
package	jar:jar
install	install:install
deploy	deploy:deploy

This is an almost standard set of bindings; however, some packagings handle them differently. For example, a project that is purely metadata (packaging value is pom) only binds goals to the install and deploy phases (for a complete list of goal-to-build-phase bindings of some of the packaging types, refer to the Lifecycle Reference).

Note that for some packaging types to be available, you may also need to include a particular plugin in the <build> section of your POM and specify <extensions>true</extensions> for that plugin. One example of a plugin that requires this is the Plexus plugin, which provides a plexus-application and plexus-service packaging.

[top].

Plugins

The second way to add goals to phases is to configure plugins in your project. Plugins are artifacts that provide goals to Maven. Furthermore, a plugin may have one or more goals wherein each goal represents a capability of that plugin. For example, the Compiler plugin has two goals: compile and testCompile. The former compiles the source code of your main code, while the latter compiles the source code of your test code.

As you will see in the later sections, plugins can contain information that indicates which lifecycle phase to bind a goal to. Note that adding the plugin on its own is not enough information - you must also specify the goals you want to run as part of your build.

The goals that are configured will be added to the goals already bound to the lifecycle from the packaging selected. If more than one goal is bound to a particular phase, the order used is that those from the packaging are executed first, followed by those configured in the POM. Note that you can use the <executions> element to gain more control over the order of particular goals.

For example, the Modello plugin binds by default its goal modello:java to the generate-sources phase (Note: The modello:java goal generates Java source codes). So to use the Modello plugin and have it generate sources from a model and incorporate that into the build, you would add the following to your POM in the <plugins> section of <build>:

...
 <plugin>
   <groupId>org.codehaus.modello</groupId>
   <artifactId>modello-maven-plugin</artifactId>
   <version>1.8.1</version>
   <executions>
     <execution>
       <configuration>
         <models>
           <model>src/main/mdo/maven.mdo</model>
         </models>
         <version>4.0.0</version>
       </configuration>
       <goals>
         <goal>java</goal>
       </goals>
     </execution>
   </executions>
 </plugin>
...

You might be wondering why that <executions> element is there. That is so that you can run the same goal multiple times with different configuration if needed. Separate executions can also be given an ID so that during inheritance or the application of profiles you can control whether goal configuration is merged or turned into an additional execution.

When multiple executions are given that match a particular phase, they are executed in the order specified in the POM, with inherited executions running first.

Now, in the case of modello:java, it only makes sense in the generate-sources phase. But some goals can be used in more than one phase, and there may not be a sensible default. For those, you can specify the phase yourself. For example, let's say you have a goal display:time that echos the current time to the commandline, and you want it to run in the process-test-resources phase to indicate when the tests were started. This would be configured like so:

...
 <plugin>
   <groupId>com.mycompany.example</groupId>
   <artifactId>display-maven-plugin</artifactId>
   <version>1.0</version>
   <executions>
     <execution>
       <phase>process-test-resources</phase>
       <goals>
         <goal>time</goal>
       </goals>
     </execution>
   </executions>
 </plugin>
...

[top].

Lifecycle Reference

The following lists all build phases of the default, clean and site lifecycles, which are executed in the order given up to the point of the one specified.

Clean Lifecycle

Phase	Description
pre-clean	execute processes needed prior to the actual project cleaning
clean	remove all files generated by the previous build
post-clean	execute processes needed to finalize the project cleaning

Default Lifecycle

Phase	Description
validate	validate the project is correct and all necessary information is available.
initialize	initialize build state, e.g. set properties or create directories.
generate-sources	generate any source code for inclusion in compilation.
process-sources	process the source code, for example to filter any values.
generate-resources	generate resources for inclusion in the package.
process-resources	copy and process the resources into the destination directory, ready for packaging.
compile	compile the source code of the project.
process-classes	post-process the generated files from compilation, for example to do bytecode enhancement on Java classes.
generate-test-sources	generate any test source code for inclusion in compilation.
process-test-sources	process the test source code, for example to filter any values.
generate-test-resources	create resources for testing.
process-test-resources	copy and process the resources into the test destination directory.
test-compile	compile the test source code into the test destination directory
process-test-classes	post-process the generated files from test compilation, for example to do bytecode enhancement on Java classes.
test	run tests using a suitable unit testing framework. These tests should not require the code be packaged or deployed.
prepare-package	perform any operations necessary to prepare a package before the actual packaging. This often results in an unpacked, processed version of the package.
package	take the compiled code and package it in its distributable format, such as a JAR.
pre-integration-test	perform actions required before integration tests are executed. This may involve things such as setting up the required environment.
integration-test	process and deploy the package if necessary into an environment where integration tests can be run.
post-integration-test	perform actions required after integration tests have been executed. This may including cleaning up the environment.
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.

Site Lifecycle

Phase	Description
pre-site	execute processes needed prior to the actual project site generation
site	generate the project's site documentation
post-site	execute processes needed to finalize the site generation, and to prepare for site deployment
site-deploy	deploy the generated site documentation to the specified web server

[top].

Built-in Lifecycle Bindings

Some phases have goals bound to them by default. And for the default lifecycle, these bindings depend on the packaging value. Here are some of the goal-to-build-phase bindings.

Clean Lifecycle Bindings

Phase	plugin:goal
clean	clean:clean

Default Lifecycle Bindings - Packaging ejb / ejb3 / jar / par / rar / war

Phase	plugin:goal
process-resources	resources:resources
compile	compiler:compile
process-test-resources	resources:testResources
test-compile	compiler:testCompile
test	surefire:test
package	ejb:ejb or ejb3:ejb3 or jar:jar or par:par or rar:rar or war:war
install	install:install
deploy	deploy:deploy

Default Lifecycle Bindings - Packaging ear

Phase	plugin:goal
generate-resources	ear:generate-application-xml
process-resources	resources:resources
package	ear:ear
install	install:install
deploy	deploy:deploy

Default Lifecycle Bindings - Packaging maven-plugin

Phase	plugin:goal
generate-resources	plugin:descriptor
process-resources	resources:resources
compile	compiler:compile
process-test-resources	resources:testResources
test-compile	compiler:testCompile
test	surefire:test
package	jar:jar and plugin:addPluginArtifactMetadata
install	install:install
deploy	deploy:deploy

Default Lifecycle Bindings - Packaging pom

Phase	plugin:goal
package
install	install:install
deploy	deploy:deploy

Site Lifecycle Bindings

Phase	plugin:goal
site	site:site
site-deploy	site:deploy

References

The full Maven lifecycle is defined by the components.xml file in the maven-core module, with associated documentation for reference.

Default lifecycle bindings are defined in a separate default-bindings.xml descriptor.

See Lifecycles Reference and Plugin Bindings for default Lifecycle Reference for latest documentation taken directly from source code.

[top].

Source: http://adamcin.net/vltpack-maven-plugin/