Throughout this book, we introduce Maven plugins, talking about Maven Project Object Model (POM) files, settings files, and profiles. There are going to be times when you need a tool to help you make sense of some of the models that Maven is using and what goals are available on a specific plugin. The Maven Help plugin allows you to list active Maven profiles, display an effective POM, print the effective settings, or list the attributes of a Maven plugin.
The Maven Help plugin has four goals. The first three
goals—active-profiles, effective-pom, and
+effective-settings+—describe a particular project and must be run in
the base directory of a project. The last goal—+describe+—is slightly
more complex, showing you information about a plugin or a plugin
goal. The following commands provide some general information about
the four goals:
- help:active-profiles
- Lists the profiles (project, user, global) which are active for the build.
- help:effective-pom
- Displays the effective POM for the current build, with the active profiles factored in.
- help:effective-settings
- Prints out the calculated settings for the project, given any profile enhancement and the inheritance of the global settings into the user-level settings.
- help:describe
-
Describes the attributes of a plugin. This need not run under an
existing project directory. You must at least give the
groupIdandartifactIdof the plugin you wish to describe.
Once you start using Maven, you’ll spend most of your time trying to
get more information about Maven Plugins: How do plugins work? What
are the configuration parameters? What are the goals? The
help:describe goal is something you’ll be using very frequently to
retrieve this information. With the plugin parameter you can specify
a plugin you wish to investigate, passing in either the plugin prefix
(e.g. maven-help-plugin as help) or the
groupId:artifact[:version], where version is optional. For example,
the following command uses the Help plugin’s describe goal to print
out information about the Maven Help plugin.
$ mvn help:describe -Dplugin=help ... Group Id: org.apache.maven.plugins Artifact Id: maven-help-plugin Version: 2.0.1 Goal Prefix: help Description: The Maven Help plugin provides goals aimed at helping to make sense out of the build environment. It includes the ability to view the effective POM and settings files, after inheritance and active profiles have been applied, as well as a describe a particular plugin goal to give usage information. ...
Executing the describe goal with the plugin parameter printed out
the Maven coordinates for the plugin, the goal prefix, and a brief
description of the plugin. While this information is helpful, you’ll
usually be looking for more detail than this. If you want the Help
plugin to print a full list of goals with parameters, execute the
help:describe goal with the parameter full as follows:
$ mvn help:describe -Dplugin=help -Dfull ... Group Id: org.apache.maven.plugins Artifact Id: maven-help-plugin Version: 2.0.1 Goal Prefix: help Description: The Maven Help plugin provides goals aimed at helping to make sense out of the build environment. It includes the ability to view the effective POM and settings files, after inheritance and active profiles have been applied, as well as a describe a particular plugin goal to give usage information. Mojos: Goal: 'active-profiles' Description: Lists the profiles which are currently active for this build. Implementation: org.apache.maven.plugins.help.ActiveProfilesMojo Language: java Parameters: [0] Name: output Type: java.io.File Required: false Directly editable: true Description: This is an optional parameter for a file destination for the output of this mojo...the listing of active profiles per project. [1] Name: projects Type: java.util.List Required: true Directly editable: false Description: This is the list of projects currently slated to be built by Maven. This mojo doesn't have any component requirements. ... removed the other goals ...
This option is great for discovering all of a plugin’s goals as well
as their parameters. But sometimes this is far more information than
necessary. To get information about a single goal, set the mojo
parameter as well as the plugin parameter. The following command
lists all of the information about the Compiler plugin’s compile
goal.
$ mvn help:describe -Dplugin=compiler -Dmojo=compile -Dfull
