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。
<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
<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
<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：
<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）：
[...] <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：
<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。
<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：<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
<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
<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>