Different Maven configurations for different goals

Question

I have a Maven project which includes a Maven plugin (the Liquibase Maven plugin) which exposes different goals. Two of these goals (update and diff) need different parameters which are in conflict between them (because the semantics of the two is different), so I need to give Maven different properties in the two goal executions.

That's what I've done

<plugin>
    <groupId>org.liquibase</groupId>
    <artifactId>liquibase-maven-plugin</artifactId>
    <version>3.4.1</version>

    <!-- This configuration is used for every goal except "diff" -->
    <configuration>
        <propertyFile>src/main/resources/liquibase.properties</propertyFile>
        <promptOnNonLocalDatabase>false</promptOnNonLocalDatabase>
    </configuration>
    <executions>
        <execution>
            <id>default-cli</id>
            <goals>
                <goal>diff</goal>
            </goals>
            <!-- This configuration is used for the "diff" goal -->
            <configuration>
                <propertyFile>src/main/resources/liquibaseDiff.properties</propertyFile>
                <promptOnNonLocalDatabase>false</promptOnNonLocalDatabase>
            </configuration>
        </execution>
    </executions>
</plugin>

However, this configuration is wrong because for each goal (diff, update of the others) only the liquibaseDiff.properties file is used.

Is there any way to pass different configurations for different goals in Maven?

Answer 1

Configuration of plugins can be done in two different locations:

• Globally for all executions. The global configuration is done with the <configuration> element under <plugin>. This configuration in inherited by all executions.
• Per execution. This is done using the <configuration> element under <execution>.

In your example, consider this POM:

<plugin>
    <groupId>org.liquibase</groupId>
    <artifactId>liquibase-maven-plugin</artifactId>
    <version>3.4.1</version>
    <configuration>
        <!-- put the configuration here that is common to all executions -->
    </configuration>
    <executions>
        <execution>
            <id>diff</id>
            <goals>
                <goal>diff</goal>
            </goals>
            <configuration>
                <!-- put the specific configuration of the diff goal here, this will inherit from the global configuration -->
            </configuration>
        </execution>
        <execution>
            <id>update</id>
            <goals>
                <goal>update</goal>
            </goals>
            <configuration>
                <!-- put the specific configuration of the update goal here, this will inherit from the global configuration -->
            </configuration>
        </execution>
    </executions>
</plugin>

The default inheritance behavior is to merge the content of the configuration element according to element name. If the child POM has a particular element, that value becomes the effective value. If the child POM does not have an element, but the parent does, the parent value becomes the effective value.

In case of conflicts, you can control the default inheritance performed by Maven using combine.children and combine.self. Quoting the Maven docs:

combine.children="append" results in the concatenation of parent and child elements, in that order. combine.self="override", on the other hand, completely suppresses parent configuration.

---

In addition to this, you need to be aware that when executing a Maven command, on the command line, that directly invokes a goal, such as mvn liquibase:diff, it creates a new execution with an id that is default-cli. As such, since the specific configuration above of the goal diff is done in an execution with id diff, it will not be used. This is actually normal, since the same goal of the same plugin could be present in multiple execution blocks with different configuration: which one should be used if it is executed on the command line, without additional information?

Typically, this situation is solved in 2 manners:

• Execute on the command line a specific execution, i.e. the one you configured. This is possible since Maven 3.3.1 and you would execute

  mvn liquibase:diff@diff
  

  The @diff in the command above refers to the unique <id> of the execution that is configured in the POM.

• Bind your execution to a specific phase of the Maven lifecycle, and let it be executed with the normal flow of the lifecycle. This is generally the prefered solution. In the example above, we could, for example, add a <phase>test</phase> in the execution block of the diff execution; and then Maven will execute it when the test phase is ran during the course of the build.