Maven - Build Life Cycle

What is Build Lifecycle?

A Build Lifecycle is a well defined sequence of phases which define the order in which the goals are to be executed. Here phase represents a stage in life cycle.
As an example, a typical Maven Build Lifecycle consists of following sequence of phases

Phase	Handles	Description
prepare-resources	resource copying	Resource copying can be customized in this phase.
compile	compilation	Source code compilation is done in this phase.
package	packaging	This phase creates the JAR / WAR package as mentioned in packaging in POM.xml.
install	installation	This phase installs the package in local / remote maven repository.

There are always pre and post phases which can be used to register goals which must run prior to or after a particular phase.
When Maven starts building a project, it steps through a defined sequence of phases and executes goals which are registered with each phase. Maven has following three standard lifecycles:

• clean
• default(or build)
• site

A goal represents a specific task 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.

mvn clean dependency:copy-dependencies package

Here the clean phase will be executed first, and then the dependency:copy-dependencies goal will be executed, and finally package phase will be executed.

Clean Lifecycle

When we execute mvn post-clean command, Maven invokes the clean lifecycle consisting of the following phases.

• pre-clean
• clean
• post-clean

Maven clean goal (clean:clean) is bound to the clean phase in the clean lifecycle. Its clean:clean goal deletes the output of a build by deleting the build directory. Thus when mvn clean command executes, Maven deletes the build directory.
We can customize this behavior by mentioning goals in any of the above phases of clean life cycle.
In the following example, We'll attach maven-antrun-plugin:run goal to the pre-clean, clean, and post-clean phases. This will allow us to echo text messages displaying the phases of the clean lifecycle.
We've created a pom.xml in C:\MVN\project folder.

<project xmlns="http://maven.apache.org/POM/4.0.0"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
   http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.companyname.projectgroup</groupId>
<artifactId>project</artifactId>
<version>1.0</version>
<build>
<plugins>
   <plugin>
   <groupId>org.apache.maven.plugins</groupId>
   <artifactId>maven-antrun-plugin</artifactId>
   <version>1.1</version>
   <executions>
      <execution>
         <id>id.pre-clean</id>
         <phase>pre-clean</phase>
         <goals>
            <goal>run</goal>
         </goals>
         <configuration>
            <tasks>
               <echo>pre-clean phase</echo>
            </tasks>
         </configuration>
      </execution>
      <execution>
         <id>id.clean</id>
         <phase>clean</phase>
         <goals>
          <goal>run</goal>
         </goals>
         <configuration>
            <tasks>
               <echo>clean phase</echo>
            </tasks>
         </configuration>
      </execution>
      <execution>
         <id>id.post-clean</id>
         <phase>post-clean</phase>
         <goals>
            <goal>run</goal>
         </goals>
         <configuration>
            <tasks>
               <echo>post-clean phase</echo>
            </tasks>
         </configuration>
      </execution>
   </executions>
   </plugin>
</plugins>
</build>
</project>

Now open command console, go to the folder containing pom.xml and execute the following mvn command.

C:\MVN\project>mvn post-clean

Maven will start processing and display all the phases of clean life cycle

[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building project 1.0
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-antrun-plugin:1.1:run (id.pre-clean) @ project ---
[INFO] Executing tasks
     [echo] pre-clean phase
[INFO] Executed tasks
[INFO]
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ project ---
[INFO]
[INFO] --- maven-antrun-plugin:1.1:run (id.clean) @ project ---
[INFO] Executing tasks
     [echo] clean phase
[INFO] Executed tasks
[INFO]
[INFO] --- maven-antrun-plugin:1.1:run (id.post-clean) @ project ---
[INFO] Executing tasks
     [echo] post-clean phase
[INFO] Executed tasks
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.078 s
[INFO] Finished at: 2015-09-26T08:03:06+05:30
[INFO] Final Memory: 7M/247M
[INFO] ------------------------------------------------------------------------

You can try tuning mvn clean command which will display pre-clean and clean, nothing will be executed for post-clean phase.

Default (or Build) Lifecycle

This is the primary life cycle of Maven and is used to build the application. It has following 23 phases.

Lifecycle Phase	Description
validate	Validates whether project is correct and all necessary information is available to complete the build process.
initialize	Initializes build state, for example set properties
generate-sources	Generate any source code to be included in compilation phase.
process-sources	Process the source code, for example, filter any value.
generate-resources	Generate resources to be included in the package.
process-resources	Copy and process the resources into the destination directory, ready for packaging phase.
compile	Compile the source code of the project.
process-classes	Post-process the generated files from compilation, for example to do bytecode enhancement/optimization on Java classes.
generate-test-sources	Generate any test source code to be included in compilation phase.
process-test-sources	Process the test source code, for example, filter any values.
test-compile	Compile the test source code into the test destination directory.
process-test-classes	Process the generated files from test code file compilation.
test	Run tests using a suitable unit testing framework(Junit is one).
prepare-package	Perform any operations necessary to prepare a package before the actual packaging.
package	Take the compiled code and package it in its distributable format, such as a JAR, WAR, or EAR file.
pre-integration-test	Perform actions required before integration tests are executed. For example, 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. For example, cleaning up the environment.
verify	Run any check-ups to verify the package is valid and meets quality criterias.
install	Install the package into the local repository, which can be used as a dependency in other projects locally.
deploy	Copies the final package to the remote repository for sharing with other developers and projects.

There are few important concepts related to Maven Lifecycles which are wroth to mention:

• When a phase is called via Maven command, for example mvn compile, only phases upto and including that phase will execute.
• Different maven goals will be bound to different phases of Maven lifecycle depending upon the type of packaging (JAR / WAR / EAR).

In the following example, We'll attach maven-antrun-plugin:run goal to few of the phases of Build lifecycle. This will allow us to echo text messages displaying the phases of the lifecycle.
We've updated pom.xml in C:\MVN\project folder.

 
<project xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
  http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.companyname.projectgroup</groupId>
<artifactId>project</artifactId>
<version>1.0</version>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-antrun-plugin</artifactId>
<version>1.1</version>
<executions>
   <execution>
      <id>id.validate</id>
      <phase>validate</phase>
      <goals>
         <goal>run</goal>
      </goals>
      <configuration>
         <tasks>
            <echo>validate phase</echo>
         </tasks>
      </configuration>
   </execution>
   <execution>
      <id>id.compile</id>
      <phase>compile</phase>
      <goals>
         <goal>run</goal>
      </goals>
      <configuration>
         <tasks>
            <echo>compile phase</echo>
         </tasks>
      </configuration>
   </execution>
   <execution>
      <id>id.test</id>
      <phase>test</phase>
      <goals>
         <goal>run</goal>
      </goals>
      <configuration>
         <tasks>
            <echo>test phase</echo>
         </tasks>
      </configuration>
   </execution>
   <execution>
         <id>id.package</id>
         <phase>package</phase>
         <goals>
            <goal>run</goal>
         </goals>
         <configuration>
         <tasks>
            <echo>package phase</echo>
         </tasks>
      </configuration>
   </execution>
   <execution>
      <id>id.deploy</id>
      <phase>deploy</phase>
      <goals>
         <goal>run</goal>
      </goals>
      <configuration>
      <tasks>
         <echo>deploy phase</echo>
      </tasks>
      </configuration>
   </execution>
</executions>
</plugin>
</plugins>
</build>
</project>

Now open command console, go the folder containing pom.xml and execute the following mvn command.

C:\MVN\project>mvn compile

Maven will start processing and display phases of build life cycle upto compile phase.

[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building project 1.0
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-antrun-plugin:1.1:run (id.validate) @ project ---
[INFO] Executing tasks
     [echo] validate phase
[INFO] Executed tasks
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ project --
-
[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources,
i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory C:\MVN\project\src\main\resources
[INFO]
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ project ---
[INFO] No sources to compile
[INFO]
[INFO] --- maven-antrun-plugin:1.1:run (id.compile) @ project ---
[INFO] Executing tasks
     [echo] compile phase
[INFO] Executed tasks
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 3.704 s
[INFO] Finished at: 2015-09-26T08:22:05+05:30
[INFO] Final Memory: 10M/247M
[INFO] ------------------------------------------------------------------------

Site Lifecycle

Maven Site plugin is generally used to create fresh documentation to create reports, deploy site etc.
Phases

• pre-site
• site
• post-site
• site-deploy

In the following example, We'll attach maven-antrun-plugin:run goal to all the phases of Site lifecycle. This will allow us to echo text messages displaying the phases of the lifecycle.
We've updated pom.xml in C:\MVN\project folder.

<project xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
  http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.companyname.projectgroup</groupId>
<artifactId>project</artifactId>
<version>1.0</version>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-antrun-plugin</artifactId>
<version>1.1</version>
   <executions>
      <execution>
         <id>id.pre-site</id>
         <phase>pre-site</phase>
         <goals>
            <goal>run</goal>
         </goals>
         <configuration>
            <tasks>
               <echo>pre-site phase</echo>
            </tasks>
         </configuration>
      </execution>
      <execution>
         <id>id.site</id>
         <phase>site</phase>
         <goals>
         <goal>run</goal>
         </goals>
         <configuration>
            <tasks>
               <echo>site phase</echo>
            </tasks>
         </configuration>
      </execution>
      <execution>
         <id>id.post-site</id>
         <phase>post-site</phase>
         <goals>
            <goal>run</goal>
         </goals>
         <configuration>
            <tasks>
               <echo>post-site phase</echo>
            </tasks>
         </configuration>
      </execution>
      <execution>
         <id>id.site-deploy</id>
         <phase>site-deploy</phase>
         <goals>
            <goal>run</goal>
         </goals>
         <configuration>
            <tasks>
               <echo>site-deploy phase</echo>
            </tasks>
         </configuration>
      </execution>
   </executions>
</plugin>
</plugins>
</build>
</project>

Now open command console, go the folder containing pom.xml and execute the following mvn command.

C:\MVN\project>mvn site

Maven will start processing and display phases of site life cycle upto site phase.

[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building project 1.0
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-antrun-plugin:1.1:run (id.pre-site) @ project ---
[INFO] Executing tasks
     [echo] pre-site phase
[INFO] Executed tasks
[INFO]
[INFO] --- maven-site-plugin:3.3:site (default-site) @ project ---
[WARNING] Report plugin org.apache.maven.plugins:maven-project-info-reports-plug
in has an empty version.
[WARNING]
[WARNING] It is highly recommended to fix these problems because they threaten t
he stability of your build.
[WARNING]
[WARNING] For this reason, future Maven versions might no longer support buildin
g such malformed projects.
[INFO] configuring report plugin org.apache.maven.plugins:maven-project-info-rep
orts-plugin:2.8.1
[WARNING] No project URL defined - decoration links will not be relativized!
[INFO] Rendering site with org.apache.maven.skins:maven-default-skin:jar:1.0 ski
n.
[INFO] Generating "Dependency Convergence" report    --- maven-project-info-repo
rts-plugin:2.8.1
[INFO] Generating "Dependency Information" report    --- maven-project-info-repo
rts-plugin:2.8.1
[INFO] Generating "About" report    --- maven-project-info-reports-plugin:2.8.1
[INFO] Generating "Plugin Management" report    --- maven-project-info-reports-p
lugin:2.8.1
[INFO] Generating "Project Plugins" report    --- maven-project-info-reports-plu
gin:2.8.1
[INFO] Generating "Project Summary" report    --- maven-project-info-reports-plu
gin:2.8.1
[INFO]
[INFO] --- maven-antrun-plugin:1.1:run (id.site) @ project ---
[INFO] Executing tasks
     [echo] site phase
[INFO] Executed tasks
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 11.390 s
[INFO] Finished at: 2015-09-26T08:43:45+05:30
[INFO] Final Memory: 18M/247M
[INFO] ------------------------------------------------------------