• Create an empty Maven project.
• Create and understand the basic directory structure.

A directory that has a pom.xml file is a valid Maven project. A POM (Project Object Model) file describes what libraries are needed for your projects, which Java version to build, plugins needed by Maven, and more. Let’s create our first pom file and add some basic configuration.

First, we will create a directory called example-app. This will be our project’s root directory. Once you’ve created this folder, create a pom.xml file in the example-app directory and add the following to the POM file:

<?xml version="1.0" encoding="UTF-8"?>

<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>org.example</groupId>
  <artifactId>example-app</artifactId>
  <version>1.0-SNAPSHOT</version>

  <name>example-app</name>
  <url>http://www.example.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>11</maven.compiler.source>
    <maven.compiler.target>11</maven.compiler.target>
  </properties>

  <dependencies>

  </dependencies>

  <build>
    <plugins>
      <plugin>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.10.1</version>
      </plugin>
    </plugins>
  </build>
</project>

We’ll start examining the pom file from the line where <groupId>org.example</groupId> starts. Everything before that contains the XML namespaces and the XML model version which you won’t have to modify. We’ll look at the sections below that and discuss them.

Since all projects need to be unique Maven provides a standard way to distinguish between projects using coordinates.

<groupId>org.example</groupId>
<artifactId>example-app</artifactId>
<version>1.0-SNAPSHOT</version>

1. groupId: This is usually the group, company, or department creating the project. We generally use the domain name in reverse order. In this case, the company domain is [example.org](http://example.org) so we’ve written it as org.example in the POM file.
2. artifactId: A unique name for the project under the groupId. For example, if the company is creating multiple libraries, each library would have a unique artifactId but the same groupId.
3. version: This indicates the current version of the project. Each new release would get a new version. You can check out what a SNAPSHOT version means here.

In this diagram, the first layer represents the groupId, the second layer represents artifactId, and finally the final layer represents the version.

The <name> tag is a human-friendly name for the project. If it’s not specified, the artifactId will be used as the project name. The <url> tag links to the project so other tools can parse the project’s link.

<name>example-app</name>
<url>http://www.example.org</url>

The properties section specifies values that can be used anywhere within a POM or as default values by plugins.

<properties>
  <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  <maven.compiler.source>11</maven.compiler.source>
  <maven.compiler.target>11</maven.compiler.target>
</properties>

The <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> specifies the encoding for resources like .properties and text files. Maven will use the operating system’s default encoding if it’s not specified which could lead to incompatibility across systems.

The <maven.compiler.source>11</maven.compiler.source> tag specifies the minimum Java version required for the project and the <maven.compiler.target>11</maven.compiler.target> tag specifies what version the project is expected to run on.

This section is used for defining additional libraries required for the project. We will add dependencies later and discuss them in detail in later lessons.

<dependencies>

</dependencies>

The <build> tag is used for specifying the project directory structure and managing plugins.

Plugins are used by Maven to extend its core functionality. Some of the common plugins are:

• Compiler Plugin: this contains the logic for compiling the project.
• Jar Plugin: contains instructions for creating JAR files.
• Surefire Plugin: used for executing unit tests.

<build>
  <plugins>
    <plugin>
      <artifactId>maven-compiler-plugin</artifactId>
      <version>3.10.1</version>
    </plugin>
  </plugins>
</build>

There are several other plugins that we can use and even build our own. A plugin simply consists of code that performs various tasks during the build process. We’ve only added the maven-compiler-plugin to this project which is used to compile Java sources.

We can use the mvn validate command to validate the pom.xml file. Here’s the output of running the command on a project with a valid file:

[INFO] Scanning for projects...
[INFO]
[INFO] ----------------------< org.example:example-app >-----------------------
[INFO] Building example-app 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  0.034 s
[INFO] Finished at: 2022-06-28T21:08:06-04:00
[INFO] ------------------------------------------------------------------------

We’ve learned how to create a Maven project and learned the basic properties of the POM file.