5.2. Portability through Maven Profiles
A profile in Maven is an alternative set of configuration values which
set or override default values. Using a profile, you can customize a
build for different environments. Profiles are configured in the
pom.xml and are given an identifier. Then you can run Maven with a
command-line flag that tells Maven to execute goals in a specific
profile. The following pom.xml uses a production profile to
override the default settings of the Compiler plugin.
Using a Maven Profile to Override Production Compiler Settings.
<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/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>org.sonatype.mavenbook</groupId>
<artifactId>simple</artifactId>
<packaging>jar</packaging>
<version>1.0-SNAPSHOT</version>
<name>simple</name>
<url>http://maven.apache.org</url>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
</dependencies>
<profiles> (1)
<profile>
<id>production</id> (2)
<build> (3)
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<debug>false</debug> (4)
<optimize>true</optimize>
</configuration>
</plugin>
</plugins>
</build>
</profile>
</profiles>
</project>
In this example, we’ve added a profile named production that
overrides the default configuration of the Maven Compiler
plugin. Let’s examine the syntax of this profile in detail.
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(1)
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The profiles element is in the pom.xml, it contains one or
more profile elements. Since profiles override the default settings
in a pom.xml, the profiles element is usually listed as the last
element in a pom.xml.
|
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(2)
|
Each profile has to have an id element. This id element
contains the name which is used to invoke this profile from the
command-line. A profile is invoked by passing the -P<profile_id>
command-line argument to Maven.
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(3)
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A profile element can contain many of the elements which can
appear under the project element of a POM XML Document. In this
example, we’re overriding the behavior of the Compiler plugin and we
have to override the plugin configuration which is normally enclosed
in a build and a plugins element.
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|
(4)
|
We’re overriding the configuration of the Maven Compiler
plugin. We’re making sure that the bytecode produced by the production
profile doesn’t contain debug information and that the bytecode has
gone through the compiler’s optimization routines.
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To execute mvn install under the production profile, you need to
pass the -Pproduction argument on the command-line. To verify that
the production profile overrides the default Compiler plugin
configuration, execute Maven with debug output enabled (-X) as
follows:
~/examples/profile $ mvn clean install -Pproduction -X
... (omitting debugging output) ...
[DEBUG] Configuring mojo 'o.a.m.plugins:maven-compiler-plugin:2.0.2:testCompile'
[DEBUG] (f) basedir = ~\examples\profile
[DEBUG] (f) buildDirectory = ~\examples\profile\target
...
[DEBUG] (f) compilerId = javac
[DEBUG] (f) *debug = false*
[DEBUG] (f) failOnError = true
[DEBUG] (f) fork = false
[DEBUG] (f) *optimize = true*
[DEBUG] (f) outputDirectory = \
~\svnw\sonatype\examples\profile\target\test-classes
[DEBUG] (f) outputFileName = simple-1.0-SNAPSHOT
[DEBUG] (f) showDeprecation = false
[DEBUG] (f) showWarnings = false
[DEBUG] (f) staleMillis = 0
[DEBUG] (f) verbose = false
[DEBUG] -- end configuration --
... (omitting debugging output) ...
This excerpt from the debug output of Maven shows the configuration of
the Compiler plugin under the production profile. As shown in the
output, debug is set to false and optimize is set to true.
5.2.1. Overriding a Project Object Model
While the previous example showed you how to override the default
configuration properties of a single Maven plugin, you still don’t
know exactly what a Maven profile is allowed to override. The
short-answer to that question is that a Maven profile can override
almost everything that you would have in a pom.xml. The Maven POM
contains an element under project called profiles containing a
project’s alternate configurations, and under this element are profile
elements which define each profile. Each profile must have an id,
and other than that, it can contain almost any of the elements one
would expect to see under project. The following XML document shows
all of the elements, a profile is allowed to override.
Elements Allowed in a Profile.
<project>
<profiles>
<profile>
<build>
<defaultGoal>...</defaultGoal>
<finalName>...</finalName>
<resources>...</resources>
<testResources>...</testResources>
<plugins>...</plugins>
</build>
<reporting>...</reporting>
<modules>...</modules>
<dependencies>...</dependencies>
<dependencyManagement>...</dependencyManagement>
<distributionManagement>...</distributionManagement>
<repositories>...</repositories>
<pluginRepositories>...</pluginRepositories>
<properties>...</properties>
</profile>
</profiles>
</project>
A profile can override an element shown with ellipses. A profile can
override the final name of a project’s artifact in a profile, the
dependencies, and the behavior of a project’s build via plugin
configuration. A profile can also override the configuration of
distribution settings depending on the profile; for example, if you
need to publish an artifact to a staging server in a staging profile,
you would create a staging profile which overrides the
distributionManagement element in a profile.
