Maven by Example

3.2. Creating a Simple Project

To start a new Maven project, use the Maven Archetype plugin from the command line. Run the archetype:generate goal, select default archetype suggested by pressing "Enter". This will use the archetype org.apache.maven.archetypes:maven-archetype-quickstart. Press "Enter" again to confirm the latest version of the archetype and then "Enter" to confirm the supplied parameters.

Warning

At the time of publication, the default maven-archetype-quickstart was item #312 in a list of 860 available archetypes. As more and more projects release Maven archetypes, this list will change and the number for the default archetype may change. When you run archetype:generate as shown below, the default maven-archetype-quickstart will be selected by default.

$ mvn archetype:generate -DgroupId=org.sonatype.mavenbook \
-DartifactId=simple \
-Dpackage=org.sonatype.mavenbook \
-Dversion=1.0-SNAPSHOT
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building Maven Stub Project (No POM) 1
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] >>> maven-archetype-plugin:2.2:generate (default-cli) @ standalone-pom >>>
[INFO]
[INFO] <<< maven-archetype-plugin:2.2:generate (default-cli) @ standalone-pom <<<
[INFO]
[INFO] --- maven-archetype-plugin:2.2:generate (default-cli) @ standalone-pom ---
[INFO] Generating project in Interactive mode
[INFO] No archetype defined. Using maven-archetype-quickstart (org.apache.maven.archetypes:maven-archetype-quickstart:1.0)
Choose archetype:
...
312: remote -> org.apache.maven.archetypes:maven-archetype-quickstart (An archetype which contains a sample Maven project.)
Choose a number or apply filter (format: [groupId:]artifactId, case sensitive contains): 312:
Choose org.apache.maven.archetypes:maven-archetype-quickstart version:
1: 1.0-alpha-1
2: 1.0-alpha-2
3: 1.0-alpha-3
4: 1.0-alpha-4
5: 1.0
6: 1.1
Choose a number: 6:
[INFO] Using property: groupId = org.sonatype.mavenbook
[INFO] Using property: artifactId = simple
[INFO] Using property: version = 1.0-SNAPSHOT
[INFO] Using property: package = org.sonatype.mavenbook
Confirm properties configuration:
groupId: org.sonatype.mavenbook
artifactId: simple
version: 1.0-SNAPSHOT
package: org.sonatype.mavenbook
 Y: :
[INFO] ----------------------------------------------------------------------------
[INFO] Using following parameters for creating project from Old (1.x) Archetype: maven-archetype-quickstart:1.1
[INFO] ----------------------------------------------------------------------------
[INFO] Parameter: groupId, Value: org.sonatype.mavenbook
[INFO] Parameter: packageName, Value: org.sonatype.mavenbook
[INFO] Parameter: package, Value: org.sonatype.mavenbook
[INFO] Parameter: artifactId, Value: simple
[INFO] Parameter: basedir, Value: /Volumes/mac-data/dev/github/sonatype
[INFO] Parameter: version, Value: 1.0-SNAPSHOT
[INFO] project created from Old (1.x) Archetype in dir: /Volumes/mac-data/dev/github/sonatype/simple
[INFO] BUILD SUCCESS
...

mvn is the Maven command. archetype:generate is called a Maven goal. An archetype is defined as “an original model or type after which other similar things are patterned; a prototype.” A number of archetypes are available in Maven for anything from a simple application to a complex web application, and the archetype:generate offers a list of archetypes to choose from. In this chapter, we are going to use the most basic archetype to create a simple skeleton starter project. The plugin is the prefix archetype, and the goal is generate.

Once we’ve generated a project, take a look at the directory structure Maven created under the simple directory:

simple/(1)
simple/pom.xml(2)
/src/
/src/main/(3)
/main/java
/src/test/(4)
/test/java

This generated directory adheres to the Maven Standard Directory Layout. We’ll get into more details later in this chapter, but for now, let’s just try to understand these few basic directories:

(1)

The Maven Archetype plugin creates a directory simple/ that matches the artifactId. This is known as the project’s base directory.

(2)

Every Maven project has what is known as a Project Object Model (POM) in a file named pom.xml. This file describes the project, configures plugins, and declares dependencies.

(3)

Our project’s source code and resources are placed under src/main. In the case of our simple Java project this will consist of a few Java classes and some properties file. In another project, this could be the document root of a web application or configuration files for an application server. In a Java project, Java classes are placed in src/main/java and classpath resources are placed in src/main/resources.

(4)

Our project’s test cases are located in src/test. Under this directory, Java classes such as JUnit or TestNG tests are placed in src/test/java, and classpath resources for tests are located in src/test/resources.

The Maven Archetype plugin generated a single class org.sonatype.mavenbook.App, which is a 13-line Java class with a static main function that prints out a message:

package org.sonatype.mavenbook;

/**
 * Hello world!
 *
 */
public class App
{
    public static void main( String[] args )
    {
        System.out.println( "Hello World!" );
    }
}

The simplest Maven archetype generates the simplest possible program: a program which prints "Hello World!" to standard output.