Convention over configuration

Convention over configuration is one of the main design philosophies behind Apache Maven. Let's go through a few examples.

A complete Maven project can be created using the following code snippet in pom.xml file:

<project>
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.packt</groupId>
  <artifactId>sample-one</artifactId>
  <version>1.0.0</version>
</project>

Tip

Downloading the example code

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Note

The Maven POM file starts with the <project> element. Always define the <project/> element with the corresponding schema. Some tools can't validate the file without it.

<project xmlns=http://maven.apache.org/POM/4.0.0xmlns:xsi=………xsi:schemaLocation="…">

Copy the previous configuration element and create a pom.xml file out of it. Then, place it in a directory called chapter-01 and create the following child directories under it:

• chapter-01/src/main/java
• chapter-01/src/test/java

Now, you can place your Java code under chapter-01/src/main/java and test cases under chapter-01/src/test/java. Use the following command to run the Maven build:

$ mvn clean install

This little configuration is tied up with many conventions:

• The Java source code is available at {base-dir}/src/main/java
• Test cases are available at {base-dir}/src/test/java
• A JAR file type of artifact is produced
• Compiled class files are copied into {base-dir}/target/classes
• The final artifact is copied into {base-dir}/target
• The linkhttp://repo.maven.apache.org/maven2is used as the repository

If someone needs to override the default, conventional behavior of Maven, that is possible too. The following sample pom.xml file shows how to override some of the preceding default values:

<project>
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.packt</groupId>
  <artifactId>sample-one</artifactId>
  <version>1.0.0</version>
  <packaging>jar</packaging>

  <build>
    <sourceDirectory>${basedir}/src/main/java</sourceDirectory>
    <testSourceDirectory>${basedir}/src/test/java
    </testSourceDirectory>
    <outputDirectory>${basedir}/target/classes
    </outputDirectory>
  </build>
</project>