Sometimes you want your pom.xml to do different things on localhost vs. when running on heroku.

Maven profiles, along with the Spring Boot *.properties files are one way to acheive this.

The code below, when added to a Maven pom.xml creates two different profiles called localhost and heroku:

Note that:

You can put a localhost.properties file in src/main/config/localhost that will override the shared properties in application.properties, and a heroku.properties in the src/main/config/heroku directory.
You can specify different dependencies, e.g. to use the H2 database on localhost, but postgres on heroku.
You can put a data.sql file in src/main/resources, but use these settings to control when it does and does not get loaded:
- In localhost.properties: spring.datasource.initialization-mode=always
- In heroku.properties: spring.datasource.initialization-mode=never

However, Maven profiles have limitations: As the jar is usually packaged and run separately at runtime, the profile will behave however it is configured at packaging/build time rather than runtime, when the jar is already fully built.

Notably, multiple profiles can be active at once–this does come with some additional complications: once a property is set for a Maven lifecycle stage, it cannot change. This can lead to odd resolutions if multiple maven profiles overlap.

Additionally, Maven profiles differ from Spring profiles in that Maven profiles instruct Maven how to behave, and can have the same or differing names from Spring profiles. A Maven profile can be used to set a Spring profile.

   <profiles>
        <profile>
            <id>localhost</id>
            <build>
                <resources>
                    <resource>
                        <directory>src/main/resources</directory>
                    </resource>
                    <resource>
                        <directory>src/main/config/localhost</directory>
                    </resource>
                </resources>
            </build>
            <dependencies>
                <dependency>
                    <groupId>com.h2database</groupId>
                    <artifactId>h2</artifactId>
                    <scope>runtime</scope>
                 </dependency>
            </dependencies>
        </profile>
        <profile>
            <id>heroku</id>
            <activation>
                <activeByDefault>true</activeByDefault>
            </activation>
            <build>
                <resources>
                    <resource>
                        <directory>src/main/resources</directory>
                    </resource>
                    <resource>
                        <directory>src/main/config/heroku</directory>
                    </resource>
                </resources>

            </build>
            <dependencies>
                <dependency>
                    <groupId>org.postgresql</groupId>
                    <artifactId>postgresql</artifactId>
                </dependency>

                <dependency>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-starter-jdbc</artifactId>
                </dependency>
            </dependencies>
        </profile>
    </profiles>

How can I tell which profile(s) is/are active?

This command tells you which profile(s) are active:

mvn help:active-profiles

More on Profiles

Maven profiles have limitations: As the jar is usually packaged and run separately at runtime, the profile will behave however it is configured at packaging/build time rather than runtime, when the jar is already fully built.