What Do id, phase, and goals Mean in Maven Plugins?

In Maven, when defining a plugin execution inside <executions>, the elements id, phase, and goals determine when and how the plugin runs during the build lifecycle.

Let's break it down:

🔹 1. <id> (Optional, But Useful)

• The <id> is a unique name for the execution.
• It helps differentiate multiple executions of the same plugin.
• It does not affect execution itself—it's just a label.

✅ Example:

<execution>
    <id>prepare-agent</id>  <!-- Just a name, used for reference -->
    <goals>
        <goal>prepare-agent</goal>
    </goals>
</execution>

⚠ If you remove <id>, Maven still runs the execution, but you can't reference it by name.

🔹 2. <phase> (Defines When It Runs)

• The <phase> tells Maven when to run this execution.
• Maven has a lifecycle with default phases like:
  • compile → Compiles Java code.
  • test → Runs unit tests.
  • package → Packages code into .jar or .war.
  • verify → Validates before finishing the build.
  • install → Installs the package into the local repository.
  • deploy → Deploys the artifact.

✅ Example:

<execution>
    <id>report</id>
    <phase>verify</phase>  <!-- This runs AFTER tests are completed -->
    <goals>
        <goal>report</goal>
    </goals>
</execution>

🚀 Why use verify?

• Tests finish in the test phase, but the JaCoCo report is generated in verify so it doesn't interfere with tests.

⚠ If <phase> is missing, Maven does NOT know when to run it!