Maven POM

POM( Project Object Model，项目对象模型 ) 是 Maven 工程的基本工作单元，是一个XML文件，包含了项目的基本信息，用于描述项目如何构建，声明项目依赖，等等。

执行任务或目标时，Maven 会在当前目录中查找 POM。它读取 POM，获取所需的配置信息，然后执行目标。

POM 中可以指定以下配置：

项目依赖
插件
执行目标
项目构建 profile
项目版本
项目开发者列表
相关邮件列表信息

在创建 POM 之前，我们首先需要描述项目组 (groupId), 项目的唯一ID。

<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>

所有 POM 文件都需要 project 元素和三个必需字段：groupId，artifactId，version。

节点	描述
project	工程的根标签。
modelVersion	模型版本需要设置为 4.0。
groupId	这是工程组的标识。它在一个组织或者项目中通常是唯一的。例如，一个银行组织 com.companyname.project-group 拥有所有的和银行相关的项目。
artifactId	这是工程的标识。它通常是工程的名称。例如，消费者银行。groupId 和 artifactId 一起定义了 artifact 在仓库中的位置。
version	这是工程的版本号。在 artifact 的仓库中，它用来区分不同的版本。例如： com.company.bank:consumer-banking:1.0 com.company.bank:consumer-banking:1.1

父（Super）POM

父（Super）POM是 Maven 默认的 POM。所有的 POM 都继承自一个父 POM（无论是否显式定义了这个父 POM）。父 POM 包含了一些可以被继承的默认设置。因此，当 Maven 发现需要下载 POM 中的依赖时，它会到 Super POM 中配置的默认仓库 http://repo1.maven.org/maven2 去下载。

Maven 使用 effective pom（Super pom 加上工程自己的配置）来执行相关的目标，它帮助开发者在 pom.xml 中做尽可能少的配置，当然这些配置可以被重写。

使用以下命令来查看 Super POM 默认配置：

mvn help:effective-pom

接下来我们创建目录 MVN/project，在该目录下创建 pom.xml，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.companyname.project-group</groupId>  <artifactId>project</artifactId>  <version>1.0</version> </project>

在命令控制台，进入 MVN/project 目录，执行以下命令：

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

Maven 将会开始处理并显示 effective-pom。

[INFO] Scanning for projects...
Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-clean-plugin/2.5/maven-clean-plugin-2.5.pom
...
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 01:36 min
[INFO] Finished at: 2018-09-05T11:31:28+08:00
[INFO] Final Memory: 15M/149M
[INFO] ------------------------------------------------------------------------

Effective POM 的结果就像在控制台中显示的一样，经过继承、插值之后，使配置生效。

<?xml version="1.0" encoding="UTF-8"?>             <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 h ttp://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> <build> <sourceDirectory>C:\MVN\project\src\main\java</sourceDirectory> <scriptSourceDirectory>src/main/scripts</scriptSourceDirectory> <testSourceDirectory>C:\MVN\project\src\test\java</testSourceDirectory> <outputDirectory>C:\MVN\project\target\classes</outputDirectory> <testOutputDirectory>C:\MVN\project\target\test-classes</testOutputDirectory> <resources> <resource> <mergeId>resource-0</mergeId> <directory>C:\MVN\project\src\main\resources</directory> </resource> </resources> <testResources> <testResource> <mergeId>resource-1</mergeId> <directory>C:\MVN\project\src\test\resources</directory> </testResource> </testResources> <directory>C:\MVN\project\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-2</version> </plugin> <plugin> <artifactId>maven-clean-plugin</artifactId> <version>2.2</version> </plugin> <plugin> <artifactId>maven-compiler-plugin</artifactId> <version>2.0.2</version> </plugin> <plugin> <artifactId>maven-dependency-plugin</artifactId> <version>2.0</version> </plugin> <plugin> <artifactId>maven-deploy-plugin</artifactId> <version>2.4</version> </plugin> <plugin> <artifactId>maven-ear-plugin</artifactId> <version>2.3.1</version> </plugin> <plugin> <artifactId>maven-ejb-plugin</artifactId> <version>2.1</version> </plugin> <plugin> <artifactId>maven-install-plugin</artifactId> <version>2.2</version> </plugin> <plugin> <artifactId>maven-jar-plugin</artifactId> <version>2.2</version> </plugin> <plugin> <artifactId>maven-javadoc-plugin</artifactId> <version>2.5</version> </plugin> <plugin> <artifactId>maven-plugin-plugin</artifactId> <version>2.4.3</version> </plugin> <plugin> <artifactId>maven-rar-plugin</artifactId> <version>2.2</version> </plugin> <plugin> <artifactId>maven-release-plugin</artifactId> <version>2.0-beta-8</version> </plugin> <plugin> <artifactId>maven-resources-plugin</artifactId> <version>2.3</version> </plugin> <plugin> <artifactId>maven-site-plugin</artifactId> <version>2.0-beta-7</version> </plugin> <plugin> <artifactId>maven-source-plugin</artifactId> <version>2.0.4</version> </plugin> <plugin> <artifactId>maven-surefire-plugin</artifactId> <version>2.4.3</version> </plugin> <plugin> <artifactId>maven-war-plugin</artifactId> <version>2.1-alpha-2</version> </plugin> </plugins> </pluginManagement> <plugins> <plugin> <artifactId>maven-help-plugin</artifactId> <version>2.1.1</version> </plugin> </plugins> </build> <repositories> <repository> <snapshots> <enabled>false</enabled> </snapshots> <id>central</id> <name>Maven Repository Switchboard</name> <url>http://repo1.maven.org/maven2</url> </repository> </repositories> <pluginRepositories> <pluginRepository> <releases> <updatePolicy>never</updatePolicy> </releases> <snapshots> <enabled>false</enabled> </snapshots> <id>central</id> <name>Maven Plugin Repository</name> <url>http://repo1.maven.org/maven2</url> </pluginRepository> </pluginRepositories> <reporting> <outputDirectory>C:\MVN\project\target/site</outputDirectory> </reporting> </project>

在上面的 pom.xml 中，你可以看到 Maven 在执行目标时需要用到的默认工程源码目录结构、输出目录、需要的插件、仓库和报表目录。

Maven 的 pom.xml 文件也不需要手工编写。

Maven 提供了大量的原型插件来创建工程，包括工程结构和 pom.xml。

POM 标签大全详解

<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/4.0.0http://maven.apache.org/maven-v4_0_0.xsd">  <parent>  <artifactId />  <groupId />  <version />  <relativePath /> </parent>  <modelVersion>4.0.0</modelVersion>  <groupId>asia.banseon</groupId>  <artifactId>banseon-maven2</artifactId>  <packaging>jar</packaging>  <version>1.0-SNAPSHOT</version>  <name>banseon-maven</name>  <url>http://www.baidu.com/banseon</url>  <description>A maven project to study maven.</description>  <prerequisites>  <maven /> </prerequisites>  <issueManagement>  <system>jira</system>  <url>http://jira.baidu.com/banseon</url> </issueManagement>  <ciManagement>  <system />  <url />  <notifiers>  <notifier>  <type />  <sendOnError />  <sendOnFailure />  <sendOnSuccess />  <sendOnWarning />  <address />  <configuration /> </notifier> </notifiers> </ciManagement>  <inceptionYear />  <mailingLists>  <mailingList>  <name>Demo</name>  <post>[email protected]</post>  <subscribe>[email protected]</subscribe>  <unsubscribe>[email protected]</unsubscribe>  <archive>http:/hi.baidu.com/banseon/demo/dev/</archive> </mailingList> </mailingLists>  <developers>  <developer>  <id>HELLO WORLD</id>  <name>banseon</name>  <email>[email protected]</email>  <url />  <roles> <role>Project Manager</role> <role>Architect</role> </roles>  <organization>demo</organization>  <organizationUrl>http://hi.baidu.com/banseon</organizationUrl>  <properties> <dept>No</dept> </properties>  <timezone>-5</timezone> </developer> </developers>  <contributors>  <contributor> <name /> <email /> <url /> <organization /> <organizationUrl /> <roles /> <timezone /> <properties /> </contributor> </contributors>  <licenses>  <license>  <name>Apache 2</name>  <url>http://www.baidu.com/banseon/LICENSE-2.0.txt</url>  <distribution>repo</distribution>  <comments>A business-friendly OSS license</comments> </license> </licenses>  <scm>  <connection> scm:svn:http://svn.baidu.com/banseon/maven/banseon/banseon-maven2-trunk(dao-trunk) </connection>  <developerConnection> scm:svn:http://svn.baidu.com/banseon/maven/banseon/dao-trunk </developerConnection>  <tag />  <url>http://svn.baidu.com/banseon</url> </scm>  <organization>  <name>demo</name>  <url>http://www.baidu.com/banseon</url> </organization>  <build>  <sourceDirectory />  <scriptSourceDirectory />  <testSourceDirectory />  <outputDirectory />  <testOutputDirectory />  <extensions>  <extension>  <groupId />  <artifactId />  <version /> </extension> </extensions>  <defaultGoal />  <resources>  <resource>  <targetPath />  <filtering />  <directory />  <includes />  <excludes /> </resource> </resources>  <testResources>  <testResource> <targetPath /> <filtering /> <directory /> <includes /> <excludes /> </testResource> </testResources>  <directory />  <finalName />  <filters />  <pluginManagement>  <plugins>  <plugin>  <groupId />  <artifactId />  <version />  <extensions />  <executions>  <execution>  <id />  <phase />  <goals />  <inherited />  <configuration /> </execution> </executions>  <dependencies>  <dependency> ...... </dependency> </dependencies>  <inherited />  <configuration /> </plugin> </plugins> </pluginManagement>  <plugins>  <plugin> <groupId /> <artifactId /> <version /> <extensions /> <executions> <execution> <id /> <phase /> <goals /> <inherited /> <configuration /> </execution> </executions> <dependencies>  <dependency> ...... </dependency> </dependencies> <goals /> <inherited /> <configuration /> </plugin> </plugins> </build>  <profiles>  <profile>  <id />  <activation>  <activeByDefault />  <jdk />  <os>  <name>Windows XP</name>  <family>Windows</family>  <arch>x86</arch>  <version>5.1.2600</version> </os>  <property>  <name>mavenVersion</name>  <value>2.0.3</value> </property>  <file>  <exists>/usr/local/hudson/hudson-home/jobs/maven-guide-zh-to-production/workspace/ </exists>  <missing>/usr/local/hudson/hudson-home/jobs/maven-guide-zh-to-production/workspace/ </missing> </file> </activation>  <build> <defaultGoal /> <resources> <resource> <targetPath /> <filtering /> <directory /> <includes /> <excludes /> </resource> </resources> <testResources> <testResource> <targetPath /> <filtering /> <directory /> <includes /> <excludes /> </testResource> </testResources> <directory /> <finalName /> <filters /> <pluginManagement> <plugins>  <plugin> <groupId /> <artifactId /> <version /> <extensions /> <executions> <execution> <id /> <phase /> <goals /> <inherited /> <configuration /> </execution> </executions> <dependencies>  <dependency> ...... </dependency> </dependencies> <goals /> <inherited /> <configuration /> </plugin> </plugins> </pluginManagement> <plugins>  <plugin> <groupId /> <artifactId /> <version /> <extensions /> <executions> <execution> <id /> <phase /> <goals /> <inherited /> <configuration /> </execution> </executions> <dependencies>  <dependency> ...... </dependency> </dependencies> <goals /> <inherited /> <configuration /> </plugin> </plugins> </build>  <modules />  <repositories>  <repository> <releases> <enabled /> <updatePolicy /> <checksumPolicy /> </releases> <snapshots> <enabled /> <updatePolicy /> <checksumPolicy /> </snapshots> <id /> <name /> <url /> <layout /> </repository> </repositories>  <pluginRepositories>  <pluginRepository> <releases> <enabled /> <updatePolicy /> <checksumPolicy /> </releases> <snapshots> <enabled /> <updatePolicy /> <checksumPolicy /> </snapshots> <id /> <name /> <url /> <layout /> </pluginRepository> </pluginRepositories>  <dependencies>  <dependency> ...... </dependency> </dependencies>  <reports />  <reporting> ...... </reporting>  <dependencyManagement> <dependencies>  <dependency> ...... </dependency> </dependencies> </dependencyManagement>  <distributionManagement> ...... </distributionManagement>  <properties /> </profile> </profiles>  <modules />  <repositories>  <repository>  <releases>  <enabled />  <updatePolicy />  <checksumPolicy /> </releases>  <snapshots> <enabled /> <updatePolicy /> <checksumPolicy /> </snapshots>  <id>banseon-repository-proxy</id>  <name>banseon-repository-proxy</name>  <url>http://192.168.1.169:9999/repository/</url>  <layout>default</layout> </repository> </repositories>  <pluginRepositories>  <pluginRepository> ...... </pluginRepository> </pluginRepositories>  <dependencies> <dependency>  <groupId>org.apache.maven</groupId>  <artifactId>maven-artifact</artifactId>  <version>3.8.1</version>  <type>jar</type>  <classifier></classifier>  <scope>test</scope>  <systemPath></systemPath>  <exclusions> <exclusion> <artifactId>spring-core</artifactId> <groupId>org.springframework</groupId> </exclusion> </exclusions>  <optional>true</optional> </dependency> </dependencies>  <reports></reports>  <reporting>  <excludeDefaults />  <outputDirectory />  <plugins>  <plugin>  <groupId />  <artifactId />  <version />  <inherited />  <configuration />  <reportSets>  <reportSet>  <id />  <configuration />  <inherited />  <reports /> </reportSet> </reportSets> </plugin> </plugins> </reporting>  <dependencyManagement> <dependencies>  <dependency> ...... </dependency> </dependencies> </dependencyManagement>  <distributionManagement>  <repository>  <uniqueVersion /> <id>banseon-maven2</id> <name>banseon maven2</name> <url>file://${basedir}/target/deploy</url> <layout /> </repository>  <snapshotRepository> <uniqueVersion /> <id>banseon-maven2</id> <name>Banseon-maven2 Snapshot Repository</name> <url>scp://svn.baidu.com/banseon:/usr/local/maven-snapshot</url> <layout /> </snapshotRepository>  <site>  <id>banseon-site</id>  <name>business api website</name>  <url> scp://svn.baidu.com/banseon:/var/www/localhost/banseon-web </url> </site>  <downloadUrl />  <relocation>  <groupId />  <artifactId />  <version />  <message /> </relocation>  <status /> </distributionManagement>  <properties /> </project>