The Maven style for Java is mainly:

• White space: One space after control statements and between arguments (i.e. if ( foo ) instead of if(foo)), myFunc( foo, bar, baz ) instead of myFunc(foo,bar,baz)). No spaces after methods names (i.e. void myMethod(), myMethod( "foo" ))
• Indentation: Always use 4 space indents and never use tabs!
• Blocks: Always enclose with a new line brace.
• Line wrapping: Always use a 120-column line width for Java code and Javadoc.
• Readingness: Specify code grouping members, if needed. For instance in a Mojo class, you could have:

  public class MyMojo
  {
      // ----------------------------------------------------------------------
      // Mojo components
      // ----------------------------------------------------------------------
  
      /**
       * Artifact factory.
       *
       * @component
       */
      private ArtifactFactory artifactFactory;
  
      ...
  
      // ----------------------------------------------------------------------
      // Mojo parameters
      // ----------------------------------------------------------------------
  
      /**
       * The POM.
       *
       * @parameter expression="${project}"
       * @required
       */
      private MavenProject project;
  
      ...
  
      // ----------------------------------------------------------------------
      // Mojo options
      // ----------------------------------------------------------------------
      ...
  
      // ----------------------------------------------------------------------
      // Public methods
      // ----------------------------------------------------------------------
  
      /**
       * {@inheritDoc}
       */
      public void execute()
          throws MojoExecutionException
      {
        ...
      }
  
      // ----------------------------------------------------------------------
      // Protected methods
      // ----------------------------------------------------------------------
      ...
  
      // ----------------------------------------------------------------------
      // Private methods
      // ----------------------------------------------------------------------
      ...
  
      // ----------------------------------------------------------------------
      // Static methods
      // ----------------------------------------------------------------------
      ...
  }

The following sections show how to set up the code style for Maven in IDEA and Eclipse. It is strongly preferred that patches use this style before they are applied.

For consistency reasons, our Java code convention is mainly:

• Naming: Constants (i.e. static final members) values should always be in upper case. Using short, descriptive names for classes and methods.
• Organization: Avoid using a lot of public inner classes. Prefer interfaces instead of default implementation.
• Modifier: Avoid using final modifier on all member variables and arguments. Prefer using private or protected member instead of public member.
• Exceptions: Throw meaningful exceptions to makes debugging and testing more easy.
• Documentation: Document public interfaces well, i.e. all non-trivial public and protected functions should include Javadoc that indicates what it does. Note: it is an ongoing convention for the Maven Team.
• Testing: All non-trivial public classes should include corresponding unit or IT tests.

TO BE DISCUSSED

The Maven style for XML files is mainly:

• Indentation: Always use 2 space indents, unless you're wrapping a new XML tags line in which case you should indent 4 spaces.
• Line Breaks: Always use a new line with indentation for complex XML types and no line break for simple XML types. Always use a new line to separate XML sections or blocks, for instance:

  <aTag>
    <simpleType>This is a simple type</simpleType>
  
    <complexType>
      <simpleType>This is a complex type</simpleType>
    </complexType>
  </aTag>

  In some cases, adding comments could improve the readability of blocks, for instance:

      <!-- Simple XML documentation                                               -->

  or

      <!-- ====================================================================== -->
      <!-- Block documentation                                                    -->
      <!-- ====================================================================== -->

No generic code convention exists yet for XML files.

The team has voted during the end of June 2008 to follow a specific POM convention to ordering POM elements. The consequence of this vote is that the Maven project descriptor is no more considered as the reference for the ordering.

The following is the recommended ordering for all Maven POM files:

<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/>

  <parent/>

  <groupId/>
  <artifactId/>
  <version/>
  <packaging/>

  <name/>
  <description/>
  <url/>
  <inceptionYear/>
  <organization/>
  <licenses/>

  <developers/>
  <contributors/>

  <mailingLists/>

  <prerequisites/>

  <modules/>

  <scm/>
  <issueManagement/>
  <ciManagement/>
  <distributionManagement/>

  <properties/>

  <dependencyManagement/>
  <dependencies/>

  <repositories/>
  <pluginRepositories/>

  <build/>

  <reporting/>

  <profiles/>
</project>

Comments:

1. The <project/> element is always on one line.
2. The blocks are voluntary separated by a new line to improve the readingness.
3. The dependencies in <dependencies/> and <dependencyManagement/> tags have no specific ordering. Developers are free to choose the ordering, but grouping dependencies by topics (like groupId i.e. org.apache.maven) is a good practice.

Note: There existing two alternativs to change order of a pom file Tidy Maven Plugin or the maven-sortpom-plugin.

For consistency and readability reasons, XDOC files should respect:

• Metadata: Always specify metadata in the <properties/> tag.
• Sections: Always use a new line with indentation for <section/> tags.

For readability reasons, FML files should respect:

• FAQ: Always use a new line with indentation for <faq/> tags.