One of the core motivations for Maven project profiles was to provide for environment-specific configuration settings. In a development environment, you might want to produce bytecode with debug information and you might want to configure your system to use a development database instance. In a production environment you might want to produce a signed JAR and configure the system to use a production database. In this chapter, we defined a number of environments with identifiers like dev and prod. A simpler way to do this would be to define profiles that are activated by environment properties and to use these common environment properties across all of your projects.

For example, if every project had a development profile activated by a property named environment.type having a value of dev, and if those same projects had a production profile activated by a property named environment.type having a value of prod, you could simply pass in the appropriate property value on the command-line to ensure that your builds target the correct environment. You can then use this property to activate profiles defined in a project's pom.xml as follows. Let's take a look at how a project's pom.xml would define a profile activated by environment.type having the value dev.

<project>
  ...
  <profiles>
    <profile>
      <id>development</id>
      <activation>
        <activeByDefault>true</activeByDefault>
        <property>
          <name>environment.type</name>
          <value>dev</value>
        </property>
      </activation>
      <properties>
        <database.driverClassName>com.mysql.jdbc.Driver</database.driverClassName>
        <database.url>
          jdbc:mysql://localhost:3306/app_dev
        </database.url>
        <database.user>development_user</database.user>
        <database.password>development_password</database.password>
      </properties>
    </profile>
    <profile>
      <id>production</id>
      <activation>
        <property>
          <name>environment.type</name>
          <value>prod</value>
        </property>
      </activation>
      <properties>
        <database.driverClassName>com.mysql.jdbc.Driver</database.driverClassName>
        <database.url>jdbc:mysql://master01:3306,slave01:3306/app_prod</database.url>
        <database.user>prod_user</database.user>
      </properties>
    </profile>
  </profiles>
</project>

This project defines some properties like database.url and database.user which might be used to configure another Maven plugin configured in the pom.xml. There are plugins available that can manipulate the database, run SQL, and plugins like the Maven Hibernate3 plugin which can generate annotated model objects for use in persistence frameworks. A few of these plugins, can be configured in a pom.xml using these properties. These properties could also be used to filter resources. If we needed to target the development environment, we would just run the following command:

~/examples/profiles $ mvn install

Because the development profile is active by default, and because there are no other profiles activated, running mvn help:active-profiles will show that the development profile is active. Now, the activeByDefault option will only work if no other profiles are active. If you wanted to be sure that the development profile would be active for a given build, you could explicitly pass in the environment.type variable as follows:

~/examples/profiles $ mvn install -Denvironment.type=dev

Alternatively, if we need to activate the production profile, we could always run Maven with:

~/examples/profiles $ mvn install -Denvironment.type=prod

To test which profiles are active for a given build, use mvn help:active-profiles.