Posts tagged maven directory structure

Few months ago, i have written an article on how to install Maven on Linux here. While i am also trying to write a guide on doing so on Windows, let me first show you a few good features of Maven 3.

The guide below walks through some Maven key commands, it is unlikely that you will configure by hand, but it is essential to know Maven’s workings through some plain command lines. For example, you may like to know that certain project dependency management features may be made through a Java IDE such as Eclipse. Discover how here http://java.sg/revolutionize-the-way-you-create-anymore-new-java-applications-with-maven-3-0/.

mvn archetype:generate

$ mvn archetype:generate

This command gives us a Maven maintained list of archetypes available for use. The result list of this command is quite long.

bash-3.2$ mvn archetype:generate
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building Maven Stub Project (No POM) 1
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] >>> maven-archetype-plugin:2.0:generate (default-cli) @ standalone-pom >>>
[INFO]
[INFO] <<< maven-archetype-plugin:2.0:generate (default-cli) @ standalone-pom <<<
[INFO]
[INFO] --- maven-archetype-plugin:2.0: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:
1: remote -> docbkx-quickstart-archetype (-)
3: remote -> simple (-)
6: remote -> gquery-archetype (-)
16: remote -> vaadin-archetype-widget (This archetype generates a Vaadin widget project for Vaadin 6.2+ and a test application.)
17: remote -> android-quickstart (Creates a skeleton for an Android application)
98: remote -> maven-archetype-quickstart (An archetype which contains a sample Maven project.)
168: remote -> struts2-archetype-blank (-)
204: remote -> appfuse-core-archetype (-)
238: remote -> ear-javaee6 (Archetype for EAR package using Java EE 6)
362: remote -> javg-minimal-archetype (-)
Choose a number: 98:

For the focus of keeping this guide short and purposeful, i have omitted the full results of the archetype listing to show you only some of the common project archetypes you will come across. The number representing each archetype is not a permanent fixture of the archetype but a  ordering that is subjected to change.

maven-archetype-quickstart

We are particularly interested in the maven-archetype-quickstart archetype for generating us a simple Java J2SE application.

Choose a number: 98: 98

So when asked to select a number representing the archetype from the list, we key in 98, and notice that by default Maven displays in the prompt the default archetype, this is especially useful for new comers.

Define value for property 'groupId': : sg.java
Define value for property 'artifactId': : helloworldMaven
Define value for property 'version':  1.0-SNAPSHOT: : 1.0-SNAPSHOT
Define value for property 'package':  sg.java: : sg.java

Next, Maven asks us to define values for the group id, artifact id, version, and package strategy that we would be employing.

groupId

group id is the unique identifier that will differential this project from another. It is most commonly represented in dot notation (sg.java.maven). For example, if i worked in SCS limited, then my group id would be com.scs, and sg.java for my own personal projects. This requirement is not restrictive, and you certainly may choose to break off the convention, just as JUnit does not follow the dot notation.

However, it is best to follow the dot notation, and represent your project in an entity manner. See this article for such reason why we should so. http://java.sg/use-sun-java-packaging-convention-please/

artifactId

artifact id is the name of the project you want it to be known by. This name differentiates one project from another you create. For example, if you a constructing an integrated billing management system, it makes sense to abbreviate the long name to “ibms”, and thereafter using it as your artifactId.

As the artifact id forms part of your packaging strategy by default, and recommended, it is best to choose a short artifact id so that you package does not become excessively long.

version

Chances are that if you not writing an API or a library, then you may not be concerned with the overall naming strategy of the project over time and change.  Certainly, jasper reports would not want to be known as jasper reports “the beginning”, jasper reports “the prelude”, and jasper reports “the finale” for each version change. Therefore, version is subjective to the incarnation of the project and allows each “version” to keep its name but well differentiated by a meaningful version number, i.e. JUnit 1.0, JUnit 2.0.

Confirm properties configuration:
groupId: sg.java
artifactId: helloworldMaven
version: 1.0-SNAPSHOT
package: sg.java
 Y: : Y
[INFO] ----------------------------------------------------------------------------
[INFO] Using following parameters for creating project from Old (1.x) Archetype: maven-archetype-quickstart:1.1
[INFO] ----------------------------------------------------------------------------
[INFO] Parameter: groupId, Value: sg.java
[INFO] Parameter: packageName, Value: sg.java
[INFO] Parameter: package, Value: sg.java
[INFO] Parameter: artifactId, Value: helloworldMaven
[INFO] Parameter: basedir, Value: C:\
[INFO] Parameter: version, Value: 1.0-SNAPSHOT
[INFO] ********************* End of debug info from resources from generated POM ***********************
[INFO] project created from Old (1.x) Archetype in dir: C:\helloworldMaven
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1:04.715s
[INFO] Finished at: Sat Jan 08 18:10:33 SGT 2011
[INFO] Final Memory: 9M/150M
[INFO] ------------------------------------------------------------------------
bash-3.2$

Maven asks us to confirm the properties, and once we do, it outputs more verbose text. It ends by generating the actual project in the file system. You may look for the Maven generated artifact sitting in your local file system in the same directory when issuing the mvn archetype:generate command.

bash-3.2$ pwd
/cygdrive/c
bash-3.2$ ls
$Recycle.Bin            Program Files              Users       csvn             hiberfil.sys          install.res.1036.dll  pagefile.sys
Documents and Settings  Program Files (x86)        VC_RED.cab  dell             install.exe           install.res.1040.dll  splash.idx
Intel                   ProgramData                Windows     drvrtmp          install.ini           install.res.1041.dll  vcredist.bmp
MSOCache                Recovery                   bea         dvmaccounts.ini  install.res.1028.dll  install.res.1042.dll
Oracle                  System Volume Information  c           globdata.ini     install.res.1031.dll  install.res.2052.dll
PerfLogs                Temp                       c3          helloworldMaven  install.res.1033.dll  install.res.3082.dll
bash-3.2$

I am actually working on a Windows system, and using cygwin and mintty to emulate a unix environment (this is really a personal preference, having worked in a data center for a year and a half, i grew very customized to looking at prompts).

As you may see from the above, i did a pwd (present working directory) to see where am i, i am located in the C:\ directory, and notice the “helloworldMaven” directory from the listing? That is the project artifact that Maven had us configured earlier and generated for us.

bash-3.2$ cd helloworldMaven/
bash-3.2$ ls
pom.xml  src
bash-3.2$ cd src
bash-3.2$ ls
main  test
bash-3.2$ cd main
bash-3.2$ ls
java
bash-3.2$ cd java
bash-3.2$ ls
sg
bash-3.2$ cd sg
bash-3.2$ ls
java
bash-3.2$ cd java/
bash-3.2$ ls
App.java
bash-3.2$ pwd
/cygdrive/c/helloworldMaven/src/main/java/sg/java
bash-3.2$

Traverse through the folders, and you may find the exact behavior of our configuration.

Lets see what the pom.xml file contains.

bash-3.2$ cat pom.xml
<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>sg.java</groupId>
  <artifactId>helloworldMaven</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>helloworldMaven</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
</project>
bash-3.2$

You may have noticed that the pom.xml included the dependencyfor junit 3.8.1. This is because that the archetype we selected (maven-archetype-quickstart) contains some examples of a normal Java project. And quite often does enterprise projects require us to have unit tests. If you are uncomfortable with it being there, you may remove the dependency. When you do so, also remove the test folder and its contents as there is a Java file (AppTest.java) inside that depends on junit libraries.

Thats all

You may now use the project artifact for development. :) Cheers.

If you continue to navigate through the project folder “helloworldMaven”, you will notice some more folders and files generated also by Maven.

Because the list of available archetypes change from time to time, just as the list maintained by yellow dog update modifier (yum CentOS / RHEL), it is not recommended to keep a “list of archetypes” cheat sheet as the preferred discovery way would be through archetype:generate.

What is a Maven Archetype?

An archetype in Maven terminology is a project terminology package and structure templating toolkit. It defines a set of standard of how some projects manage their initial structures. For example, Java EE web projects, and EJB projects both have its unique way of structuring certain folders and the placement of certain files. Maven allows us to create commonly used “ready” projects that we may base off for development in the quickest way.

Reference

Introduction to Maven Archetype http://maven.apache.org/guides/introduction/introduction-to-archetypes.html

Definition of Archetype http://dictionary.reference.com/browse/archetype

Project Object Model http://maven.apache.org/pom.html