我们会使用maven的archetype 机制来建立我们的第一个maven项目。maven中，archetype是项目模版，在加上一些用户的输入来建立一个maven的项目。我们会向你展示archetype机制如何工作。更多请参考
创建最简单的maven项目，只需要执行下面的命令就可以了
mvn archetype:generate \ -DarchetypeGroupId=org.apache.maven.archetypes \ -DgroupId=com.mycompany.app \ -DartifactId=my-app
执行命令后，首先，你会发现一个叫my-app的文件夹建立了，其中有pom.xml文件，内容如下：
<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>3.8.1</version>
<scope>test</scope>
</dependency>
</dependencies>
</project>
pom.xml里有项目的project object model。pom是maven的基本工作单元。This is important to remember because Maven is inherently project-centric in that everything revolves around the notion of a project. 简单的说，pom包含了所有项目的重要信息。更多请参考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 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 plug-ins.
- 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 <artifactId>-<version>.<extension> (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.
For a complete reference of what elements are available for use in the POM please refer to our POM Reference. Now let's get back to the project at hand.
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.
Now that we have a POM, some application sources, and some test sources you are probably asking ...