Maven3实战笔记07继承

1.  继承

之前我们学习Maven的聚合机制遗留个问题，就是多个模块的pom.xml文件的内容出现了冗余、重复的内容，解决这个问题其实使用Maven的继承机制即可，就像Java的继承一样，父类就像一个模板，子类继承自父类，那么有些通用的方法、变量都不必在子类中再重复声明了，具体Java继承在内存中的表现形式可以参考

http://suhuanzheng7784877.iteye.com/blog/1000635

和http://suhuanzheng7784877.iteye.com/blog/1000700中的部分内容。Maven的继承机制类似，在一个父级别的Maven的pom文件中定义了相关的常量、依赖、插件等等配置后，实际项目模块可以继承此父项目的pom文件，重复的项不必显示的再声明一遍了，相当于父Maven项目就是个模板，等着其他子模块去继承。不过父Maven项目要高度抽象，高度提取公共的部分（交集）。笔者使用了先前的聚合项目模块做的父模板pom，实际上很多机构也是这么实施的。

<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>com.liuyan.account</groupId>
	<artifactId>MavenAccount-aggregator</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>pom</packaging>

	<properties>
		<springversion>2.5.6</springversion>
		<junitversion>2.5.6</junitversion>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-core</artifactId>
			<version>${springversion}</version>
		</dependency>
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-beans</artifactId>
			<version>${springversion}</version>
		</dependency>
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-context</artifactId>
			<version>${springversion}</version>
		</dependency>
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-context-support</artifactId>
			<version>${springversion}</version>
		</dependency>
		<dependency>
			<groupId>javax.mail</groupId>
			<artifactId>mail</artifactId>
			<version>1.4.1</version>
		</dependency>
		<dependency>
			<groupId>junit</groupId>
			<artifactId>junit</artifactId>
			<version>4.7</version>
			<scope>test</scope>
		</dependency>
		<dependency>
			<groupId>com.icegreen</groupId>
			<artifactId>greenmail</artifactId>
			<version>1.3.1b</version>
			<scope>test</scope>
		</dependency>
	</dependencies>

	<build>
		<resources>
			<resource>
				<directory>src/main/resource</directory>
			</resource>
		</resources>
		<plugins>
			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-source-plugin</artifactId>
				<version>2.1.1</version>
				<executions>
					<execution>
						<id>buildSource</id>
						<goals>
							<goal>jar-no-fork</goal>
						</goals>
						<inherited>false</inherited>
						<configuration>
						</configuration>
					</execution>
				</executions>
			</plugin>
			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-compiler-plugin</artifactId>
				<configuration>
					<target>1.5</target>
				</configuration>
			</plugin>
		</plugins>
	</build>

	<modules>
		<module>../MavenAccount-email</module>
		<module>../MavenAccount-persist</module>
	</modules>
</project>

 这个pom文件即描述了通用的依赖模板，也列举出了聚合的模块，放心modules不会被继承。下面我们来改造一下之前的两个模块

邮件模块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/maven-v4_0_0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<artifactId>MavenAccount-email</artifactId>
	<packaging>jar</packaging>

	<parent>
		<groupId>com.liuyan.account</groupId>
		<artifactId>MavenAccount-aggregator</artifactId>
		<version>0.0.1-SNAPSHOT</version>
		<relativePath>../MavenAccount-aggregator/pom.xml</relativePath>
	</parent>

</project>

 注册模块

pom.xml