Maven Predefined Properties

1. Introduction

In this tutorial, we’ll examine predefined properties within Maven.

Properties make build configurations more dynamic, flexible, and reusable. It lets us set up different levels of properties to have default values and then easily override them whenever needed.

Let’s explore these properties in more detail.

2. Maven Predefined Properties

Maven has some handy built-in properties that we can use to streamline our configurations. We can even customize them right in our pom.xml file if needed.

They can also be used in any resource file being processed by the Maven resource plugin’s filtering features, for example, the application.properties file. We just need to wrap them in ${} whenever we use them.

2.1. Usage Example

Let’s see the usage of a property that gives the location for the output directory:

<?xml version="1.0" encoding="UTF-8"?>
<project>
    <modelVersion>4.0.0</modelVersion>
    <groupId>example.override.properties</groupId>
    <artifactId>parameter-maven-plugin</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>maven-plugin</packaging>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-plugin-plugin</artifactId>
                <version>3.2</version>
                <configuration>  
                    <outputDirectory>${project.build.directory}</outputDirectory>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

The above example shows how we can fetch the default value of the ${project.build.directory}, i.e., src/main/resources.

2.2. Overriding Property Example

Let’s see a property to give a custom build path:

<?xml version="1.0" encoding="UTF-8"?>
<project>
    <modelVersion>4.0.0</modelVersion>
    <groupId>example.override.properties</groupId>
    <artifactId>parameter-maven-plugin</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>maven-plugin</packaging>
    <build>
        <directory>src/main/resources/custom</directory>
    </build>
</project>

In the above example, we’ve overridden the default value of the property ${project.build.directory} to src/main/resources/custom by specifying the custom value in the hierarchy <project> -> <build> -> <directory>.

3. Project Information Properties

Let’s see some properties used to reference information about the project, such as its configuration, metadata, and build information:

Some properties, like ${project.groupId} and ${project.version}, can inherit default values from the parent POM if not explicitly specified.

4. Project Build Information Properties

Now, let’s dive into some specific properties that deal with where things get built and stored during the build process:

5. System Properties

On top of its own built-in properties, Maven can also tap into the system properties provided by our computer’s Java Virtual Machine (JVM) or those defined when we run a program. These properties are like handy shortcuts to environment-specific details, such as file paths or our operating system:

6. Maven-Specific Properties

Let’s see the properties that are specific to Maven’s runtime and configuration:

7. Conclusion

In this article, we explored several built-in properties that Maven provides. Essentially, they allow us to easily tweak and change settings directly within our pom.xml file.

Furthermore, it’s always a good idea to use these properties instead of hardcoding things like paths, values, or any other configurations. This makes our project much more flexible and easier to maintain.