Maven profiles are a way to define a set of configuration options for a Maven build. Profiles are used to specify different build configurations for different environments or situations. For example, you may have a development profile that uses a local database for testing and a production profile that uses a remote database.

Profiles can be activated in several ways, including by specifying a command-line option, by setting an environment variable, or by configuring the POM file. When a profile is activated, it can modify the behavior of the build by adding or removing dependencies, setting properties, or executing specific goals.

Here's an example of a profile definition in a POM file:

<profiles>
  <profile>
    <id>development</id>
    <activation>
      <activeByDefault>true</activeByDefault>
    </activation>
    <properties>
      <database.url>jdbc:mysql://localhost/mydb_dev</database.url>
    </properties>
    <dependencies>
      <dependency>
        <groupId>com.example</groupId>
        <artifactId>myapp-dev-utils</artifactId>
        <version>1.0.0</version>
      </dependency>
    </dependencies>
  </profile>
  <profile>
    <id>production</id>
    <properties>
      <database.url>jdbc:mysql://prod-db-server/mydb_prod</database.url>
    </properties>
  </profile>
</profiles>

In this example, there are two profiles defined: "development" and "production". The "development" profile is activated by default and sets the database URL property to a local development database. It also includes a dependency on a utility library for development purposes. The "production" profile sets the database URL property to a production database.

Profiles can be very useful for managing different build configurations in a flexible and customizable way.

You can use Maven profiles in different ways with the mvn command. Here are a few examples:

  1. To activate a specific profile during the build process, you can use the -P option followed by the profile ID. For example, to activate the "production" profile from the example in the previous answer, you can run:

mvn clean install -Pproduction

This will activate the "production" profile and configure the build accordingly.

  1. You can also activate multiple profiles at once by separating their IDs with commas. For example:

mvn clean install -Pdevelopment,debug

This will activate the "development" and "debug" profiles at the same time.

  1. If you have defined a default profile in your POM file, you can activate it without specifying its ID by using the -Dmaven.profiles.default option followed by true. For example:

mvn clean install -Dmaven.profiles.default=true

This will activate the default profile, if one is defined in the POM file.