Maven 简明教程

Maven - POM

POM 是 Project Object Model 的缩写。它是 Maven 中基本的工作单元。它是一个 XML 文件，作为 pom.xml 位于项目的根目录中。

POM stands for Project Object Model. It is fundamental unit of work in Maven. It is an XML file that resides in the base directory of the project as pom.xml.

POM 包含有关项目的信息，以及用于 Maven 构建项目的各种配置细节。

The POM contains information about the project and various configuration detail used by Maven to build the project(s).

POM 还包含目标和插件。在执行任务或目标时，Maven 会在当前目录中寻找 POM。它读取 POM，获取所需的配置信息，然后执行目标。可以在 POM 中指定的一些配置如下 −

POM also contains the goals and plugins. While executing a task or goal, Maven looks for the POM in the current directory. It reads the POM, gets the needed configuration information, and then executes the goal. Some of the configuration that can be specified in the POM are following −

project dependencies
plugins
goals
build profiles
project version
developers
mailing list

在创建 POM 之前，我们应该首先确定项目的 group (groupId)、其 name (artifactId) 及其版本，因为这些属性有助于在存储库中唯一地识别项目。

Before creating a POM, we should first decide the project group (groupId), its name (artifactId) and its version as these attributes help in uniquely identifying the project in repository.

POM Example

<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.companyname.project-group</groupId>
   <artifactId>project</artifactId>
   <version>1.0</version>
</project>

请注意，每个项目应该有一个 POM 文件。

It should be noted that there should be a single POM file for each project.

All POM files require the project element and three mandatory fields: groupId, artifactId, version.
Projects notation in repository is groupId:artifactId:version.
Minimal requirements for a POM −

Sr.No.	Node & Description
1	Project root This is project root tag. You need to specify the basic schema settings such as apache schema and w3.org specification.
2	Model version Model version should be 4.0.0.
3	groupId This is an Id of project’s group. This is generally unique amongst an organization or a project. For example, a banking group com.company.bank has all bank related projects.
4	artifactId This is an Id of the project. This is generally name of the project. For example, consumer-banking. Along with the groupId, the artifactId defines the artifact’s location within the repository.
5	version This is the version of the project. Along with the groupId, It is used within an artifact’s repository to separate versions from each other. For example − com.company.bank:consumer-banking:1.0 com.company.bank:consumer-banking:1.1.

Super POM

超级 POM 是 Maven 的默认 POM。所有 POM 都继承自一个父 POM 或默认 POM（明确定义或未明确定义）。这个基本 POM 被称为 Super POM ，并包含默认继承的值。

The Super POM is Maven’s default POM. All POMs inherit from a parent or default (despite explicitly defined or not). This base POM is known as the Super POM, and contains values inherited by default.

Maven 使用生效 POM（超级 POM 的配置加上项目配置）来执行相关的目标。这有助于开发者在其 pom.xml 中指定最少的配置详情。尽管可以轻松地覆盖配置。

Maven use the effective POM (configuration from super pom plus project configuration) to execute relevant goal. It helps developers to specify minimum configuration detail in his/her pom.xml. Although configurations can be overridden easily.

通过运行以下命令，可以轻松查看超级 POM 的默认配置： mvn help:effective-pom

An easy way to look at the default configurations of the super POM is by running the following command: mvn help:effective-pom

在计算机的任何目录中创建一个 pom.xml。使用上面提到的示例 pom 的内容。

Create a pom.xml in any directory on your computer.Use the content of above mentioned example pom.

在以下示例中，我们在 C:\MVN\project 文件夹中创建了一个 pom.xml。

In example below, We’ve created a pom.xml in C:\MVN\project folder.

现在打开命令控制台，转到包含 pom.xml 的文件夹并执行以下 mvn 命令。

Now open command console, go the folder containing pom.xml and execute the following mvn command.

C:\MVN\project>mvn help:effective-pom

Maven 将开始处理并显示 effective-pom。

Maven will start processing and display the effective-pom.

C:\MVN>mvn help:effective-pom
[INFO] Scanning for projects...
[INFO]
[INFO] ---------------< com.companyname.project-group:project >----------------
[INFO] Building project 1.0
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-help-plugin:3.2.0:effective-pom (default-cli) @ project ---
[INFO]
Effective POMs, after inheritance, interpolation, and profiles are applied:

[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  2.261 s
[INFO] Finished at: 2021-12-10T19:54:53+05:30
[INFO] ------------------------------------------------------------------------

C:\MVN>

在应用继承、插入和配置文件后，Effective POM 显示为控制台的结果。

Effective POM displayed as result in console, after inheritance, interpolation, and profiles are applied.

<?xml version="1.0" encoding="Cp1252"?>
<!-- ====================================================================== -->
<!--                                                                        -->
<!-- Generated by Maven Help Plugin on 2021-12-10T19:54:52+05:30            -->
<!-- See: http://maven.apache.org/plugins/maven-help-plugin/                -->
<!--                                                                        -->
<!-- ====================================================================== -->
<!-- ====================================================================== -->
<!--                                                                        -->
<!-- Effective POM for project                                              -->
<!-- 'com.companyname.project-group:project:jar:1.0'                        -->
<!--                                                                        -->
<!-- ====================================================================== -->
<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
   <modelVersion>4.0.0</modelVersion>
   <groupId>com.companyname.project-group</groupId>
   <artifactId>project</artifactId>
   <version>1.0</version>
   <repositories>
      <repository>
         <snapshots>
            <enabled>false</enabled>
         </snapshots>
         <id>central</id>
         <name>Central Repository</name>
         <url>https://repo.maven.apache.org/maven2</url>
      </repository>
   </repositories>
   <pluginRepositories>
      <pluginRepository>
         <releases>
            <updatePolicy>never</updatePolicy>
         </releases>
         <snapshots>
            <enabled>false</enabled>
         </snapshots>
         <id>central</id>
         <name>Central Repository</name>
         <url>https://repo.maven.apache.org/maven2</url>
      </pluginRepository>
   </pluginRepositories>
   <build>
      <sourceDirectory>C:\MVN\src\main\java</sourceDirectory>
      <scriptSourceDirectory>C:\MVN\src\main\scripts</scriptSourceDirectory>
      <testSourceDirectory>C:\MVN\src\test\java</testSourceDirectory>
      <outputDirectory>C:\MVN\target\classes</outputDirectory>
      <testOutputDirectory>C:\MVN\target\test-classes</testOutputDirectory>
      <resources>
         <resource>
            <directory>C:\MVN\src\main\resources</directory>
         </resource>
      </resources>
      <testResources>
         <testResource>
            <directory>C:\MVN\src\test\resources</directory>
         </testResource>
      </testResources>
      <directory>C:\MVN\target</directory>
      <finalName>project-1.0</finalName>
      <pluginManagement>
         <plugins>
            <plugin>
               <artifactId>maven-antrun-plugin</artifactId>
               <version>1.3</version>
            </plugin>
            <plugin>
               <artifactId>maven-assembly-plugin</artifactId>
               <version>2.2-beta-5</version>
            </plugin>
            <plugin>
               <artifactId>maven-dependency-plugin</artifactId>
               <version>2.8</version>
            </plugin>
            <plugin>
               <artifactId>maven-release-plugin</artifactId>
               <version>2.5.3</version>
            </plugin>
         </plugins>
      </pluginManagement>
      <plugins>
         <plugin>
            <artifactId>maven-clean-plugin</artifactId>
            <version>2.5</version>
            <executions>
               <execution>
               <id>default-clean</id>
               <phase>clean</phase>
               <goals>
                  <goal>clean</goal>
               </goals>
               </execution>
            </executions>
         </plugin>
         <plugin>
            <artifactId>maven-resources-plugin</artifactId>
            <version>2.6</version>
            <executions>
               <execution>
                  <id>default-testResources</id>
                  <phase>process-test-resources</phase>
                  <goals>
                     <goal>testResources</goal>
                  </goals>
               </execution>
               <execution>
                  <id>default-resources</id>
                  <phase>process-resources</phase>
                  <goals>
                     <goal>resources</goal>
                  </goals>
               </execution>
            </executions>
         </plugin>
         <plugin>
            <artifactId>maven-jar-plugin</artifactId>
            <version>2.4</version>
            <executions>
               <execution>
                  <id>default-jar</id>
                  <phase>package</phase>
                  <goals>
                     <goal>jar</goal>
                  </goals>
               </execution>
            </executions>
         </plugin>
         <plugin>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.1</version>
            <executions>
               <execution>
                  <id>default-compile</id>
                  <phase>compile</phase>
                  <goals>
                     <goal>compile</goal>
                  </goals>
               </execution>
               <execution>
                  <id>default-testCompile</id>
                  <phase>test-compile</phase>
                  <goals>
                     <goal>testCompile</goal>
                  </goals>
               </execution>
            </executions>
         </plugin>
         <plugin>
            <artifactId>maven-surefire-plugin</artifactId>
            <version>2.12.4</version>
            <executions>
               <execution>
                  <id>default-test</id>
                  <phase>test</phase>
                  <goals>
                     <goal>test</goal>
                  </goals>
               </execution>
            </executions>
         </plugin>
         <plugin>
            <artifactId>maven-install-plugin</artifactId>
            <version>2.4</version>
            <executions>
               <execution>
                  <id>default-install</id>
                  <phase>install</phase>
                  <goals>
                     <goal>install</goal>
                  </goals>
               </execution>
            </executions>
         </plugin>
         <plugin>
            <artifactId>maven-deploy-plugin</artifactId>
            <version>2.7</version>
            <executions>
               <execution>
                  <id>default-deploy</id>
                  <phase>deploy</phase>
                  <goals>
                     <goal>deploy</goal>
                  </goals>
               </execution>
            </executions>
         </plugin>
         <plugin>
            <artifactId>maven-site-plugin</artifactId>
            <version>3.3</version>
            <executions>
               <execution>
                  <id>default-site</id>
                  <phase>site</phase>
                  <goals>
                     <goal>site</goal>
                  </goals>
                  <configuration>
                     <outputDirectory>C:\MVN\target\site</outputDirectory>
                     <reportPlugins>
                        <reportPlugin>
                           <groupId>org.apache.maven.plugins</groupId>
                           <artifactId>maven-project-info-reports-plugin</artifactId>
                        </reportPlugin>
                     </reportPlugins>
                  </configuration>
               </execution>
               <execution>
                  <id>default-deploy</id>
                  <phase>site-deploy</phase>
                  <goals>
                     <goal>deploy</goal>
                  </goals>
                  <configuration>
                     <outputDirectory>C:\MVN\target\site</outputDirectory>
                     <reportPlugins>
                        <reportPlugin>
                           <groupId>org.apache.maven.plugins</groupId>
                           <artifactId>maven-project-info-reports-plugin</artifactId>
                        </reportPlugin>
                     </reportPlugins>
                  </configuration>
               </execution>
            </executions>
            <configuration>
               <outputDirectory>C:\MVN\target\site</outputDirectory>
               <reportPlugins>
                  <reportPlugin>
                     <groupId>org.apache.maven.plugins</groupId>
                     <artifactId>maven-project-info-reports-plugin</artifactId>
                  </reportPlugin>
               </reportPlugins>
            </configuration>
         </plugin>
      </plugins>
   </build>
   <reporting>
      <outputDirectory>C:\MVN\target\site</outputDirectory>
   </reporting>
</project>

在上面的 pom.xml 中，您可以看到 Maven 在执行所需目标时将使用的默认项目源文件夹结构、输出目录、所需的插件、存储库、报告目录。

In above pom.xml, you can see the default project source folders structure, output directory, plug-ins required, repositories, reporting directory, which Maven will be using while executing the desired goals.

也不必手动编写 Maven pom.xml。Maven 提供了许多原型插件用于创建项目，依次创建项目结构和 pom.xml。

Maven pom.xml is also not required to be written manually. Maven provides numerous archetype plugins to create projects, which in order, create the project structure and pom.xml