In this post, we will create a simple maven project and learn different maven elements. This article aims to introduce you to the simplest possible Maven project and then presents some of the core concepts that make Maven a solid build platform. After reading it, you’ll have a fundamental understanding of the build life-cycle, Maven repositories, dependency management, and the Project Object Model (POM).
Create a Maven Simple Project
On to creating your first project! In order to create the simplest of Maven projects, execute the following from the command line:
mvn -B archetype:generate \
-DarchetypeGroupId=org.apache.maven.archetypes \
-DgroupId=com.mycompany.app \
-DartifactId=my-app
Note that the whole command should be a single line. After build success, we will see the below output in the command line console.
Once you have executed this command, you will notice a few things have happened. First, you will notice that a directory named my-app has been created for the new project, and this directory contains a file named pom.xml that should look like this:
<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>com.mycompany.app</groupId>
<artifactId>my-app</artifactId>
<packaging>jar</packaging>
<version>1.0-SNAPSHOT</version>
<name>Maven Quick Start Archetype</name>
<url>http://maven.apache.org</url>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.11</version>
<scope>test</scope>
</dependency>
</dependencies>
</project>
The above pom.xml contains the Project Object Model (POM) for this project. The POM is the basic unit of work in Maven. This is important to remember because Maven is inherently project-centric in that everything revolves around the notion of a project. In short, the POM contains every important piece of information about your project and is essentially a one-stop-shopping for finding anything related to your project. Understanding the POM is important and new users are encouraged to refer to the Introduction to the POM.
This is a very simple POM but still displays the key elements every POM contains, so let's walk through each of them to familiarize you with the POM essentials:
- project - This is the top-level element in all Maven pom.xml files.
- modelVersion - This element indicates what version of the object model this POM is using. The version of the model itself changes very infrequently but it is mandatory in order to ensure the stability of use if and when the Maven developers deem it necessary to change the model.
- groupId - This element indicates the unique identifier of the organization or group that created the project. The groupId is one of the key identifiers of a project and is typically based on the fully qualified domain name of your organization. For example, org.apache.maven.plugins is the designated groupId for all Maven plugins.
- artifactId - This element indicates the unique base name of the primary artifact being generated by this project. The primary artifact for a project is typically a JAR file. Secondary artifacts like source bundles also use the artifactId as part of their final name. A typical artifact produced by Maven would have the form -. (for example, myapp-1.0.jar).
- packaging - This element indicates the package type to be used by this artifact (e.g. JAR, WAR, EAR, etc.). This not only means if the artifact produced is JAR, WAR, or EAR but can also indicate a specific lifecycle to use as part of the build process. (The lifecycle is a topic we will deal with further on in the guide. For now, just keep in mind that the indicated packaging of a project can play a part in customizing the build lifecycle.) The default value for the packaging element is JAR so you do not have to specify this for most projects.
- version - This element indicates the version of the artifact generated by the project. Maven goes a long way to help you with version management and you will often see the SNAPSHOT designator in a version, which indicates that a project is in a state of development. We will discuss the use of snapshots and how they work further on in this guide.
- name - This element indicates the display name used for the project. This is often used in Maven's generated documentation.
- url - This element indicates where the project's site can be found. This is often used in Maven's generated documentation.
- description - This element provides a basic description of your project. This is often used in Maven's generated documentation.
After the archetype generation of your first project you will also notice that the following directory structure has been created:
+ my-app
|-- pom.xml
`-- src
|-- main
| `-- java
| `-- com
| `-- mycompany
| `-- app
| `-- App.java
`-- test
`-- java
`-- com
`-- mycompany
`-- app
`-- AppTest.java
As you can see, the project created from the archetype has a POM, a source tree for your application's sources, and a source tree for your test sources. This is the standard layout for Maven projects (the application sources reside in ${basedir}/src/main/java and test sources reside in ${basedir}/src/test/java, where ${basedir} represents the directory containing pom.xml).
If you were to create a Maven project by hand this is the directory structure that we recommend using. This is a Maven convention and to learn more about it you can read our Introduction to the Standard Directory Layout.
How do I compile my application sources?
Change to the directory where pom.xml is created by archetype:generate and execute the following command to compile your application sources:
mvn compile
Upon executing this command you should see output like the following:
[INFO] ----------------------------------------------------------------------------
[INFO] Building Maven Quick Start Archetype
[INFO] task-segment: [compile]
[INFO] ----------------------------------------------------------------------------
[INFO] artifact org.apache.maven.plugins:maven-resources-plugin: \
checking for updates from central
...
[INFO] artifact org.apache.maven.plugins:maven-compiler-plugin: \
checking for updates from central
...
[INFO] [resources:resources]
...
[INFO] [compiler:compile]
Compiling 1 source file to <dir>/my-app/target/classes
[INFO] ----------------------------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO] ----------------------------------------------------------------------------
[INFO] Total time: 3 minutes 54 seconds
[INFO] Finished at: Fri Sep 23 15:48:34 GMT-05:00 2005
[INFO] Final Memory: 2M/6M
[INFO] ----------------------------------------------------------------------------
The first time you execute this (or any other) command, Maven will need to download all the plugins and related dependencies it needs to fulfill the command. From a clean installation of Maven, this can take quite a while (in the output above, it took almost 4 minutes).
If you execute the command again, Maven will now have what it needs, so it won't need to download anything new and will be able to execute the command much more quickly.
If you execute the command again, Maven will now have what it needs, so it won't need to download anything new and will be able to execute the command much more quickly.
As you can see from the output, the compiled classes were placed in ${basedir}/target/classes, which is another standard convention employed by Maven. So, if you're a keen observer, you'll notice that by using the standard conventions, the POM above is very small and you haven't had to tell Maven explicitly where any of your sources are or where the output should go. By following the standard Maven conventions, you can get a lot done with very little effort! Just as a casual comparison, let's take a look at what you might have had to do in Ant to accomplish the same thing.
Now, this is simply to compile a single tree of application sources and the Ant script shown is pretty much the same size as the POM shown above. But we'll see how much more we can do with just that simple POM!
How do I compile my test sources and run my unit tests?
Now you're successfully compiling your application's sources and now you've got some unit tests that you want to compile and execute.
Execute the following command:
mvn test
Upon executing this command you should see output like the following:
[INFO] ----------------------------------------------------------------------------
[INFO] Building Maven Quick Start Archetype
[INFO] task-segment: [test]
[INFO] ----------------------------------------------------------------------------
[INFO] artifact org.apache.maven.plugins:maven-surefire-plugin: \
checking for updates from central
...
[INFO] [resources:resources]
[INFO] [compiler:compile]
[INFO] Nothing to compile - all classes are up to date
[INFO] [resources:testResources]
[INFO] [compiler:testCompile]
Compiling 1 source file to C:\Test\Maven2\test\my-app\target\test-classes
...
[INFO] [surefire:test]
[INFO] Setting reports dir: C:\Test\Maven2\test\my-app\target/surefire-reports
-------------------------------------------------------
T E S T S
-------------------------------------------------------
[surefire] Running com.mycompany.app.AppTest
[surefire] Tests run: 1, Failures: 0, Errors: 0, Time elapsed: 0 sec
Results :
[surefire] Tests run: 1, Failures: 0, Errors: 0
[INFO] ----------------------------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO] ----------------------------------------------------------------------------
[INFO] Total time: 15 seconds
[INFO] Finished at: Thu Oct 06 08:12:17 MDT 2005
[INFO] Final Memory: 2M/8M
[INFO] ----------------------------------------------------------------------------
If you simply want to compile your test sources (but not execute the tests), you can execute the following:
In this article, we have seen a simple example of creating a maven project. In the next article, we will look into Maven Dependency Mechanism.
mvn test-compile
Comments
Post a Comment
Leave Comment