Maven Aggregation

Maven aggregation is a way to manage multiple related Maven projects within a single parent project. This is particularly useful when you have a complex project that consists of several modules or subprojects that depend on each other. Using Maven aggregation, you can build, test, and deploy all modules in the correct order with a single command.

In this tutorial, you'll learn how to set up a multi-module Maven project using Maven aggregation.

1. Create a parent project

First, create a new directory for the parent project and navigate to it. Initialize the parent project by creating a pom.xml file with the following content:

<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>parent-project</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>pom</packaging>

    <modules>
        <!-- List of modules will be added here -->
    </modules>
</project>

2. Create module projects

Next, create a new directory for each module within the parent project. Initialize each module with its own pom.xml file. Ensure that each module has a unique artifactId and set the parent's groupId, artifactId, and version in the <parent> tag:

<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <parent>
        <groupId>com.example</groupId>
        <artifactId>parent-project</artifactId>
        <version>1.0-SNAPSHOT</version>
    </parent>

    <artifactId>module-a</artifactId>
</project>

3. Add module references to the parent project

In the parent project's pom.xml file, add references to each module within the <modules> tag. Use the directory names of the module projects:

<modules>
    <module>module-a</module>
    <module>module-b</module>
    <!-- Add more modules as needed -->
</modules>

4. Define dependencies between modules (optional)

If your modules depend on one another, you can specify the dependencies in the pom.xml file of the dependent module:

<dependencies>
    <dependency>
        <groupId>com.example</groupId>
        <artifactId>module-a</artifactId>
        <version>1.0-SNAPSHOT</version>
    </dependency>
</dependencies>

5. Build the multi-module project

To build the entire multi-module project, navigate to the parent project's directory and run the following command:

mvn clean install

Maven will build each module in the order specified in the parent pom.xml file, taking into account any inter-module dependencies.

In conclusion, this tutorial demonstrated how to set up a multi-module Maven project using Maven aggregation. With this knowledge, you can efficiently manage and build

How to use Maven aggregation for multi-module projects:

Description: Maven aggregation allows managing multiple related projects as a single entity, simplifying build and dependency management.

Code:

<!-- Example: Parent POM for aggregation -->
<project>
    <groupId>com.example</groupId>
    <artifactId>parent</artifactId>
    <version>1.0.0</version>
    <packaging>pom</packaging>
    <modules>
        <module>module1</module>
        <module>module2</module>
    </modules>
</project>

Configuring parent and child POMs for Maven aggregation:

Description: Define a parent POM that includes module references. Configure child POMs with specific module details.

Code:

<!-- Example: Child POM in a multi-module project -->
<project>
    <parent>
        <groupId>com.example</groupId>
        <artifactId>parent</artifactId>
        <version>1.0.0</version>
    </parent>
    <artifactId>module1</artifactId>
    <!-- Other configurations -->
</project>

Building and packaging aggregated projects with Maven:
- Description: Use Maven commands to build and package the entire multi-module project or specific modules.
- Code:
```
# Example: Build all modules
mvn clean install

# Example: Build a specific module
cd module1
mvn clean install
```

Dependencies management in Maven aggregation:

Description: Manage dependencies across modules using the parent POM, ensuring consistent versions and configurations.

Code:

<!-- Example: Dependency management in the parent POM -->
<dependencyManagement>
    <dependencies>
        <!-- Define shared dependencies -->
    </dependencies>
</dependencyManagement>

Maven reactor and build order in aggregated projects:
- Description: Understand the Maven reactor, which determines the build order based on module interdependencies.
- Code:
```
# Example: Build a specific module and its dependencies
cd module1
mvn clean install
```