Using Maven -pl and -am to Build Specific Modules in Multi‑Module Projects

When a Maven project consists of several inter‑dependent modules, building each module individually can be time‑consuming; Maven provides a single‑command solution using the mvn clean package -pl and -am options.

The parent project P contains three sub‑modules A, B, and C. Module A depends on B and C, while B depends on C. The parent pom.xml lists the modules as:

<modules>
  <module>A</module>
  <module>B</module>
  <module>C</module>
</modules>

Each sub‑module’s pom.xml declares its dependencies, for example module A includes:

<dependency>
  <groupId>xxx.xxxx</groupId>
  <artifactId>B</artifactId>
  <version>xxxx</version>
</dependency>

To build only module A (and its required dependencies) you can run:

mvn clean package -pl A -am -P test -DskipTests=true

The key parameters are:

Parameter

Description -pl Specifies the projects to build (comma‑separated list of artifactIds). -am Also builds the modules that the specified projects depend on. -amd Builds modules that depend on the specified projects. -N Do not recurse into sub‑modules.

Examples: mvn clean install -pl A -am builds P, A, B, and C because A depends on the latter two. mvn clean install -pl C -am builds only P and C (since C has no dependencies). mvn clean install -pl C -amd builds P, C, and any modules that depend on C (e.g., B, A). mvn clean install -N builds only the parent project P without its sub‑modules.

Understanding and using these Maven options can dramatically speed up builds for large projects, often cutting build time by more than half.

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