Maven 中的继承与聚合

先贴一个parent 模块的pom.xml

<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.myproject</groupId>
  <artifactId>myproject-parent</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>pom</packaging>

  <name>myproject-parent</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <spring.version>3.2.6.RELEASE</spring.version>
  </properties>
  
  <modules>
  	 <module>../example</module>
  </modules>

  <dependencyManagement>
  <dependencies>
    <dependency>
		<groupId>org.springframework</groupId>
		<artifactId>spring-beans</artifactId>
		<version>${spring.version}</version>
    </dependency>
    <dependency>
		<groupId>org.springframework</groupId>
		<artifactId>spring-core</artifactId>
		<version>${spring.version}</version>
	</dependency>
	<dependency>
		<groupId>org.springframework</groupId>
		<artifactId>spring-context</artifactId>
		<version>${spring.version}</version>
	</dependency>
	<dependency>
		<groupId>org.springframework</groupId>
		<artifactId>spring-web</artifactId>
		<version>${spring.version}</version>
	</dependency>
	<dependency>
		<groupId>org.springframework</groupId>
		<artifactId>spring-aop</artifactId>
		<version>${spring.version}</version>
	</dependency>
	<dependency>
		<groupId>org.springframework</groupId>
		<artifactId>spring-webmvc</artifactId>
		<version>${spring.version}</version>
	</dependency>
  </dependencies>
  </dependencyManagement>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
      <scope>test</scope>
    </dependency>
   	<dependency> <!--for org.hamcrest.Matchers-->
		<groupId>org.hamcrest</groupId>
		<artifactId>hamcrest-library</artifactId>
		<version>1.3</version>
		<scope>test</scope>
	</dependency>
	
	<dependency>
		<groupId>log4j</groupId>
		<artifactId>log4j</artifactId>
		<version>1.2.17</version>
	</dependency>
	
  </dependencies>
</project>

子模块的pom.xml

<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>

  <parent>
    <groupId>com.mycompany.myproject</groupId>
    <artifactId>myproject-parent</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <relativePath>../myproject-parent/pom.xml</relativePath>
  </parent>
  
  <artifactId>peter-user</artifactId>
  <packaging>war</packaging>

  <dependencies>
    <dependency>
		<groupId>org.springframework</groupId>
		<artifactId>spring-beans</artifactId>
    </dependency>
    <dependency>
		<groupId>org.springframework</groupId>
		<artifactId>spring-core</artifactId>
	</dependency>
	<dependency>
		<groupId>org.springframework</groupId>
		<artifactId>spring-context</artifactId>
	</dependency>
	<dependency>
		<groupId>org.springframework</groupId>
		<artifactId>spring-web</artifactId>
	</dependency>
	<dependency>
		<groupId>org.springframework</groupId>
		<artifactId>spring-aop</artifactId>
	</dependency>
	<dependency>
		<groupId>org.springframework</groupId>
		<artifactId>spring-webmvc</artifactId>
	</dependency>
  </dependencies>
</project>

继承：
1.子模块可以继承parent中所有关于GAV的属性，artifactId除外
2.子模块可以继承parent中properties
3.子模块可以继承parent中的dependencies，比如子模块都不用再添加log4j的依赖了，
但是这样也容易导致子模块中添加了不需要的模块。此时需要使用dependencyManagement，子模块pom.xml中只需要添加GA，这样也省去了很多麻烦。

聚合：
将所有开放的子模块使用modules打包，这样就不需要每个模块单独编译，打包了。