pom.xml详解

一、什么是POM

Project Object Model，项目对象模型。通过xml格式保存的pom.xml文件。作用类似ant的build.xml文件，功能更强大。该文件用于管理：源代码、配置文件、开发者的信息和角色、问题追踪系统、组织信息、项目授权、项目的url、项目的依赖关系等等。

一个完整的pom.xml文件，放置在项目的根目录下。

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<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/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>

<!– The Basics –>

<groupId>…</groupId>

<artifactId>…</artifactId>

<version>…</version>

<packaging>…</packaging>

<dependencies>…</dependencies>

<parent>…</parent>

<dependencyManagement>…</dependencyManagement>

<modules>…</modules>

<properties>…</properties>

<!– Build Settings –>

<build>…</build>

<reporting>…</reporting>

<!– More Project Information –>

<name>…</name>

<description>…</description>

<url>…</url>

<inceptionYear>…</inceptionYear>

<licenses>…</licenses>

<organization>…</organization>

<developers>…</developers>

<contributors>…</contributors>

<!– Environment Settings –>

<issueManagement>…</issueManagement>

<ciManagement>…</ciManagement>

<mailingLists>…</mailingLists>

<scm>…</scm>

<prerequisites>…</prerequisites>

<repositories>…</repositories>

<pluginRepositories>…</pluginRepositories>

<distributionManagement>…</distributionManagement>

<profiles>…</profiles>

</project>

二、基本设置

1、maven的协作相关属性

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<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/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>

<groupId>org.codehaus.mojo</groupId>

<artifactId>my-project</artifactId>

<version>1.0</version>

<packaging>war</packaging>

</project>

groupId : 组织标识，例如：org.codehaus.mojo，在M2_REPO目录下，将是: org/codehaus/mojo目录。
artifactId : 项目名称，例如：my-project，在M2_REPO目录下，将是：org/codehaus/mojo/my-project目录。
version : 版本号，例如：1.0，在M2_REPO目录下，将是：org/codehaus/mojo/my-project/1.0目录。
packaging : 打包的格式，可以为：pom , jar , maven-plugin , ejb , war , ear , rar , par

2、POM之间的关系

主要用于POM文件的复用。

a）依赖关系：依赖关系列表（dependency
list）是POM的重要部分

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<dependencies>

<dependency>

<groupId>junit</groupId>

<artifactId>junit</artifactId>

<version>4.0</version>

<scope>test</scope>

</dependency>

…

</dependencies>

groupId , artifactId , version :
scope : compile(default),provided,runtime,test,system
exclusions

b）继承关系：继承其他pom.xml配置的机制。

比如父pom.xml：

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<project>

[...]

<dependencies>

<dependency>

<groupId>junit</groupId>

<artifactId>junit</artifactId>

<version>4.4</version>

<scope>test</scope>

</dependency>

</dependencies>

[...]

</project>

在子pom.xml文件继承它的依赖（还可以继承其他的：developers and contributors、plugin lists、reports lists、plugin executions with matching ids、plugin configuration）：

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[...]

<parent>

<groupId>com.devzuz.mvnbook.proficio</groupId>

<artifactId>proficio</artifactId>

<version>1.0-SNAPSHOT</version>

</parent>

[...]

在这种机制下，maven还提供了一个类似java.lang.Object的顶级父pom.xml文件：

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<project>

<modelVersion>4.0.0</modelVersion>

<name>Maven Default Project</name>

<repositories>

<repository>

<id>central</id>

<name>Maven Repository Switchboard</name>

<layout>default</layout>

<url>http://repo1.maven.org/maven2</url>

<snapshots>

<enabled>false</enabled>

</snapshots>

</repository>

</repositories>

<pluginRepositories>

<pluginRepository>

<id>central</id>

<name>Maven Plugin Repository</name>

<url>http://repo1.maven.org/maven2</url>

<layout>default</layout>

<snapshots>

<enabled>false</enabled>

</snapshots>

<releases>

<updatePolicy>never</updatePolicy>

</releases>

</pluginRepository>

</pluginRepositories>

<build>

<directory>target</directory>

<outputDirectory>target/classes</outputDirectory>

<finalName>${project.artifactId}-${project.version}</finalName>

<testOutputDirectory>target/test-classes</testOutputDirectory>

<sourceDirectory>src/main/java</sourceDirectory>

<scriptSourceDirectory>src/main/scripts</scriptSourceDirectory>

<testSourceDirectory>src/test/java</testSourceDirectory>

<resources>

<resource>

<directory>src/main/resources</directory>

</resource>

</resources>

<testResources>

<testResource>

<directory>src/test/resources</directory>

</testResource>

</testResources>

<pluginManagement>

<plugins>

<plugin>

<artifactId>maven-antrun-plugin</artifactId>

<version>1.1</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>2.3</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>2.4</version>

</plugin>

<plugin>

<artifactId>maven-plugin-plugin</artifactId>

<version>2.4.1</version>

</plugin>

<plugin>

<artifactId>maven-rar-plugin</artifactId>

<version>2.2</version>

</plugin>

<plugin>

<artifactId>maven-release-plugin</artifactId>

<version>2.0-beta-7</version>

</plugin>

<plugin>

<artifactId>maven-resources-plugin</artifactId>

<version>2.2</version>

</plugin>

<plugin>

<artifactId>maven-site-plugin</artifactId>

<version>2.0-beta-6</version>

</plugin>

<plugin>

<artifactId>maven-source-plugin</artifactId>

<version>2.0.4</version>

</plugin>

<plugin>

<artifactId>maven-surefire-plugin</artifactId>

<version>2.4.2</version>

</plugin>

<plugin>

<artifactId>maven-war-plugin</artifactId>

<version>2.1-alpha-1</version>

</plugin>

</plugins>

</pluginManagement>

</build>

<reporting>

<outputDirectory>target/site</outputDirectory>

</reporting>

<profiles>

<profile>

<id>release-profile</id>

<activation>

<property>

<name>performRelease</name>

<value>true</value>

</property>

</activation>

<build>

<plugins>

<plugin>

<inherited>true</inherited>

<groupId>org.apache.maven.plugins</groupId>

<artifactId>maven-source-plugin</artifactId>

<executions>

<execution>

<id>attach-sources</id>

<goals>

<goal>jar</goal>

</goals>

</execution>

</executions>

</plugin>

<plugin>

<inherited>true</inherited>

<groupId>org.apache.maven.plugins</groupId>

<artifactId>maven-javadoc-plugin</artifactId>

<executions>

<execution>

<id>attach-javadocs</id>

<goals>

<goal>jar</goal>

</goals>

</execution>

</executions>

</plugin>

<plugin>

<inherited>true</inherited>

<groupId>org.apache.maven.plugins</groupId>

<artifactId>maven-deploy-plugin</artifactId>

<configuration>

<updateReleaseInfo>true</updateReleaseInfo>

</configuration>

</plugin>

</plugins>

</build>

</profile>

</profiles>

</project>

可以通过下面命令查看当前pom.xml受到超pom.xml文件的影响：

mvn help:effective-pom

c）聚合关系：用于将多个maven项目聚合为一个大的项目。

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<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/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>

<groupId>org.codehaus.mojo</groupId>

<artifactId>my-parent</artifactId>

<version>2.0</version>

<modules>

<module>my-project<module>

</modules>

</project>

3、属性

maven的属性，是值的占位符，类似EL，类似ant的属性，比如${X}，可用于pom文件任何赋值的位置。有以下分类：

env.X：操作系统环境变量，比如${env.PATH}
project.x：pom文件中的属性，比如：<project><version>1.0</version></project>，引用方式：${project.version}
settings.x：settings.xml文件中的属性，比如：<settings><offline>false</offline></settings>，引用方式：${settings.offline}
Java System Properties：java.lang.System.getProperties()中的属性，比如java.home，引用方式：${java.home}
自定义：在pom文件中可以：<properties><installDir>c:/apps/cargo-installs</installDir></properties>，引用方式：${installDir}

4、构建设置

构建有两种build标签：

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<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/maven-v4_0_0.xsd">
…

<!– "Project Build" contains more elements than just the BaseBuild set –>

<build>…</build>

<profiles>

<profile>

<!– "Profile Build" contains a subset of "Project Build"s elements –>

<build>…</build>

</profile>

</profiles>

</project>

build中的主要标签：Resources和Plugins。

Resources：用于排除或包含某些资源文件

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<resources>

<resource>

<targetPath>META-INF/plexus</targetPath>

<filtering>false</filtering>

<directory>${basedir}/src/main/plexus</directory>

<includes>

<include>configuration.xml</include>

</includes>

<excludes>

<exclude>**/*.properties</exclude>

</excludes>

</resource>

</resources>

Plugins：设置构建的插件

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<build>

…

<plugins>

<plugin>

<groupId>org.apache.maven.plugins</groupId>

<artifactId>maven-jar-plugin</artifactId>

<version>2.0</version>

<extensions>false</extensions>

<inherited>true</inherited>

<configuration>

<classifier>test</classifier>

</configuration>

<dependencies>…</dependencies>

<executions>…</executions>

</plugin>