Posted on Sep 1, 2018
Maven has many different plugins and many times its very time consuming to google and find the suitable configuration to achieve your goal. Fortunately maven itself comes with help plugin which allows you to fetch all the necessary information about any plugin. As a example I will use the Spring boot plugin. The project you can easily obtain from Spring Initializr.
Our obvious starting point would be check what goals available for the plugin, below is the command to achieve the same
mvn help:describe -DgroupId=org.springframework.boot -DartifactId=spring-boot-maven-plugin
Output:
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------< org.apache.maven:standalone-pom >-------------------
[INFO] Building Maven Stub Project (No POM) 1
[INFO] --------------------------------[ pom ]---------------------------------
[INFO]
[INFO] --- maven-help-plugin:3.1.0:describe (default-cli) @ standalone-pom ---
[INFO] org.springframework.boot:spring-boot-maven-plugin:2.0.4.RELEASE
Name: Spring Boot Maven Plugin
Description: Spring Boot Maven Plugin
Group Id: org.springframework.boot
Artifact Id: spring-boot-maven-plugin
Version: 2.0.4.RELEASE
Goal Prefix: spring-boot
This plugin has 6 goals:
spring-boot:build-info
Description: Generate a build-info.properties file based the content of the
current MavenProject.
spring-boot:help
Description: Display help information on spring-boot-maven-plugin.
Call mvn spring-boot:help -Ddetail=true -Dgoal=<goal-name> to display
parameter details.
spring-boot:repackage
Description: Repackages existing JAR and WAR archives so that they can be
executed from the command line using java -jar. With layout=NONE can also
be used simply to package a JAR with nested dependencies (and no main
class, so not executable).
spring-boot:run
Description: Run an executable archive application.
spring-boot:start
Description: Start a spring application. Contrary to the run goal, this
does not block and allows other goal to operate on the application. This
goal is typically used in integration test scenario where the application
is started before a test suite and stopped after.
spring-boot:stop
Description: Stop a spring application that has been started by the 'start'
goal. Typically invoked once a test suite has completed.
For more information, run 'mvn help:describe [...] -Ddetail'
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.611 s
[INFO] Finished at: 2018-09-01T18:17:41+05:30
[INFO] ------------------------------------------------------------------------
You can see that it has given you all the goals available for the plugin. For example spring-boot:run is the plugin goal to be used when we want to run the Spring Application.
If we need to check bindings of any specific goal to the maven lifecycle phases it can be done using -Ddetail and -Dgoal=<goal name>.
Command:
mvn help:describe -Ddetail -Dgoal=start -DgroupId=org.springframework.boot -DartifactId=spring-boot-maven-plugin
Output:
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------< org.apache.maven:standalone-pom >-------------------
[INFO] Building Maven Stub Project (No POM) 1
[INFO] --------------------------------[ pom ]---------------------------------
[INFO]
[INFO] --- maven-help-plugin:3.1.0:describe (default-cli) @ standalone-pom ---
[INFO] Mojo: 'spring-boot:start'
spring-boot:start
Description: Start a spring application. Contrary to the run goal, this
does not block and allows other goal to operate on the application. This
goal is typically used in integration test scenario where the application
is started before a test suite and stopped after.
Implementation: org.springframework.boot.maven.StartMojo
Language: java
Bound to phase: pre-integration-test
Available parameters:
addResources (Default: false)
User property: spring-boot.run.addResources
Add maven resources to the classpath directly, this allows live in-place
editing of resources. Duplicate resources are removed from target/classes
to prevent them to appear twice if ClassLoader.getResources() is called.
Please consider adding spring-boot-devtools to your project instead as it
provides this feature and many more.
agent
User property: spring-boot.run.agent
Path to agent jar. NOTE: the use of agents means that processes will be
started by forking a new JVM.
arguments
User property: spring-boot.run.arguments
Arguments that should be passed to the application. On command line use
commas to separate multiple arguments.
classesDirectory (Default: ${project.build.outputDirectory})
Required: true
Directory containing the classes and resource files that should be
packaged into the archive.
excludeArtifactIds
User property: spring-boot.excludeArtifactIds
Comma separated list of artifact names to exclude (exact match).
Deprecated. as of 2.0.2 in favour of {@code excludes}
excludeGroupIds
User property: spring-boot.excludeGroupIds
Comma separated list of groupId names to exclude (exact match).
excludes
User property: spring-boot.excludes
Collection of artifact definitions to exclude. The Exclude element
defines a groupId and artifactId mandatory properties and an optional
classifier property.
folders
User property: spring-boot.run.folders
Additional folders besides the classes directory that should be added to
the classpath.
fork
User property: spring-boot.run.fork
Flag to indicate if the run processes should be forked. fork is
automatically enabled if an agent, jvmArguments or working directory are
specified, or if devtools is present.
includes
User property: spring-boot.includes
Collection of artifact definitions to include. The Include element
defines a groupId and artifactId mandatory properties and an optional
classifier property.
jmxName
The JMX name of the automatically deployed MBean managing the lifecycle
of the spring application.
jmxPort
The port to use to expose the platform MBeanServer if the application
needs to be forked.
jvmArguments
User property: spring-boot.run.jvmArguments
JVM arguments that should be associated with the forked process used to
run the application. On command line, make sure to wrap multiple values
between quotes. NOTE: the use of JVM arguments means that processes will
be started by forking a new JVM.
mainClass
User property: spring-boot.run.main-class
The name of the main class. If not specified the first compiled class
found that contains a 'main' method will be used.
maxAttempts
The maximum number of attempts to check if the spring application is
ready. Combined with the 'wait' argument, this gives a global timeout
value (30 sec by default)
noverify
User property: spring-boot.run.noverify
Flag to say that the agent requires -noverify.
profiles
User property: spring-boot.run.profiles
The spring profiles to activate. Convenience shortcut of specifying the
'spring.profiles.active' argument. On command line use commas to separate
multiple profiles.
skip (Default: false)
User property: spring-boot.run.skip
Skip the execution.
useTestClasspath (Default: false)
User property: spring-boot.run.useTestClasspath
Flag to include the test classpath when running.
wait
The number of milli-seconds to wait between each attempt to check if the
spring application is ready.
workingDirectory
User property: spring-boot.run.workingDirectory
Current working directory to use for the application. If not specified,
basedir will be used. NOTE: the use of working directory means that
processes will be started by forking a new JVM.
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.082 s
[INFO] Finished at: 2018-09-01T18:26:51+05:30
[INFO] ------------------------------------------------------------------------
As you noticed it also printed which phase this goal in our case its the start goal is bound to.
Bound to phase: pre-integration-test
This line tells us that start goal will automatically get executed during pre-integration-test maven phase
Similarly we have stop goal which is bound to post-integration-test maven lifecycle phase. So that during integration test the application will be turned on so that integration testing can be performed on it.
If we need to check what goals are invoked by any specific command execution, we can use -Dcmd and pass it the exact command,
For example below command will check what goals are executed when we execute mvn spring-boot:run
mvn help:describe -Dcmd=spring-boot:run -Ddetail
Output:
[INFO] Scanning for projects...
[INFO]
[INFO] ---------------< io.github.spsarolkar:fortune-teller-ui >---------------
[INFO] Building fortune-teller-ui 0.0.1-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-help-plugin:2.2:describe (default-cli) @ fortune-teller-ui ---
[INFO] 'spring-boot:run' is a plugin goal (aka mojo).
Mojo: 'spring-boot:run'
spring-boot:run
Description: Run an executable archive application.
Implementation: org.springframework.boot.maven.RunMojo
Language: java
Bound to phase: validate
Before this mojo executes, it will call:
Phase: 'test-compile'
Available parameters:
addResources (Default: false)
User property: spring-boot.run.addResources
Add maven resources to the classpath directly, this allows live in-place
editing of resources. Duplicate resources are removed from target/classes
to prevent them to appear twice if ClassLoader.getResources() is called.
Please consider adding spring-boot-devtools to your project instead as it
provides this feature and many more.
agent
User property: spring-boot.run.agent
Path to agent jar. NOTE: the use of agents means that processes will be
started by forking a new JVM.
arguments
User property: spring-boot.run.arguments
Arguments that should be passed to the application. On command line use
commas to separate multiple arguments.
classesDirectory (Default: ${project.build.outputDirectory})
Required: true
Directory containing the classes and resource files that should be
packaged into the archive.
excludeArtifactIds
User property: spring-boot.excludeArtifactIds
Comma separated list of artifact names to exclude (exact match).
Deprecated. as of 2.0.2 in favour of {@code excludes}
excludeGroupIds
User property: spring-boot.excludeGroupIds
Comma separated list of groupId names to exclude (exact match).
excludes
User property: spring-boot.excludes
Collection of artifact definitions to exclude. The Exclude element
defines a groupId and artifactId mandatory properties and an optional
classifier property.
folders
User property: spring-boot.run.folders
Additional folders besides the classes directory that should be added to
the classpath.
fork
User property: spring-boot.run.fork
Flag to indicate if the run processes should be forked. fork is
automatically enabled if an agent, jvmArguments or working directory are
specified, or if devtools is present.
includes
User property: spring-boot.includes
Collection of artifact definitions to include. The Include element
defines a groupId and artifactId mandatory properties and an optional
classifier property.
jvmArguments
User property: spring-boot.run.jvmArguments
JVM arguments that should be associated with the forked process used to
run the application. On command line, make sure to wrap multiple values
between quotes. NOTE: the use of JVM arguments means that processes will
be started by forking a new JVM.
mainClass
User property: spring-boot.run.main-class
The name of the main class. If not specified the first compiled class
found that contains a 'main' method will be used.
noverify
User property: spring-boot.run.noverify
Flag to say that the agent requires -noverify.
profiles
User property: spring-boot.run.profiles
The spring profiles to activate. Convenience shortcut of specifying the
'spring.profiles.active' argument. On command line use commas to separate
multiple profiles.
skip (Default: false)
User property: spring-boot.run.skip
Skip the execution.
useTestClasspath (Default: false)
User property: spring-boot.run.useTestClasspath
Flag to include the test classpath when running.
workingDirectory
User property: spring-boot.run.workingDirectory
Current working directory to use for the application. If not specified,
basedir will be used. NOTE: the use of working directory means that
processes will be started by forking a new JVM.
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 0.775 s
[INFO] Finished at: 2018-09-01T19:35:11+05:30
[INFO] ------------------------------------------------------------------------
As we can see we get below message indicating test-compile will get executed when spring-boot:run is executed
Before this mojo executes, it will call:
Phase: 'test-compile'