Maven的继承以及import作用域
Maven的pom文件中可继承的元素包括：
groupId：项目ID，项目坐标核心元素
version：项目版本
description：描述信息
organization：组织信息
inceptionYear：创始年份
url：项目URL地址
developers：开发者信息
distributionManagement：项目部署配置
issueManagement：项目缺陷跟踪系统信息
ciManagement：项目持续集成系统信息
scm：项目版本控制系统信息
mailingLists：邮件列表
properties：自定义属性
dependencies：依赖配置
dependencyManagement：依赖配置管理
repositories：仓库配置
build：构建信息，包括源码目录，输出目录，插件配置，插件管理配置
reporting：项目的报告输出目录配置，报告插件配置。
大部分配置都是说明性质的信息配置，这里主要介绍依赖配置，依赖管理配置，插件配置，插件管理配置。示例如下：
父项目配置文件：
<!-- 父项目本身除了一个pom.xml文件，不包含其它内容 --> <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.cbm.stu</groupId> <artifactId>maven-study-parent</artifactId> <version>1.0.0</version> <packaging>pom</packaging> <!-- 父项目的packing必须为pom --> <name>maven-study-parent</name> <url>http://maven.apache.org</url> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> </properties> <!-- dependencies标签中的依赖会被子项目完全继承：即父项目中有的依赖都会出现在子项目中 --> <dependencies> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.4.1</version> </dependency> </dependencies> <!-- 依赖管理中声明的依赖并不会被子项目直接继承，在子项目中需要声明，但是只需要声明groupId和artifactId --> <dependencyManagement> <dependencies> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.40</version> </dependency> <dependency> <groupId>org.postgresql</groupId> <artifactId>postgresql</artifactId> <version>42.0.0</version> </dependency> <dependency> <groupId>redis.clients</groupId> <artifactId>jedis</artifactId> <version>2.9.0</version> </dependency> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.10</version> <scope>test</scope> </dependency> </dependencies> </dependencyManagement> <build> <!-- 插件管理，可供子项目继承 --> <pluginManagement> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <version>2.1</version> <configuration> <source>1.7</source> <target>1.7</target> </configuration> </plugin> </plugins> </pluginManagement> </build> </project>
子项目配置：
<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标签声明继承的父项目信息 --> <parent> <groupId>com.cbm.stu</groupId> <artifactId>maven-study-parent</artifactId> <version>1.0.0</version> <!-- 父项目的pom.xml相对于当前项目的位置 --> <relativePath>../maven-study-parent/pom.xml</relativePath> </parent> <!-- groupId可以继承，也可以覆盖，通常不需要覆盖 --> <groupId>com.cbm.stud</groupId> <!-- 不可继承，子项目坐标的关键属性 --> <artifactId>maven-study-account</artifactId> <version>1.0.2</version> <packaging>jar</packaging> <name>maven-study-account</name> <url>http://maven.apache.org</url> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> </properties> <!-- 父项目中dependencies标签声明的依赖被直接继承，例如mybatis包 --> <dependencies> <!-- 继承自父项目的依赖，只需指明groupId和artifactId --> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> </dependency> </dependencies> <build> <plugins> <plugin> <!-- 继承自父项目的插件依赖，此处省略也可继承 --> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> </plugin> </plugins> </build> </project>
使用import属性实现依赖的多继承：
父项目a：
<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.cbm.stu</groupId> <artifactId>maven-parent-a</artifactId> <version>1.0.0</version> <packaging>pom</packaging> <name>maven-parent-a</name> <url>http://maven.apache.org</url> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> </properties> <dependencyManagement> <dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.10</version> <scope>test</scope> </dependency> </dependencies> </dependencyManagement> </project>
父项目b：
<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.cbm.stu</groupId> <artifactId>maven-parent-b</artifactId> <version>1.0.0</version> <packaging>pom</packaging> <name>maven-parent-b</name> <url>http://maven.apache.org</url> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> </properties> <dependencyManagement> <dependencies> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.4.1</version> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.40</version> </dependency> </dependencies> </dependencyManagement> </project>
继承 a 和 b 的子项目：
<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/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.cbm.stu</groupId> <artifactId>maven-study-mail</artifactId> <version>2.1</version> <packaging>jar</packaging> <name>maven-study-mail</name> <url>http://maven.apache.org</url> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> </properties> <dependencyManagement> <dependencies> <!-- 此处继承了a 和 b 两个项目，type为pom，scope 为 import --> <dependency> <groupId>com.cbm.stu</groupId> <artifactId>maven-parent-a</artifactId> <version>1.0.0</version> <type>pom</type> <scope>import</scope> </dependency> <dependency> <groupId>com.cbm.stu</groupId> <artifactId>maven-parent-b</artifactId> <version>1.0.0</version> <type>pom</type> <scope>import</scope> </dependency> </dependencies> </dependencyManagement> <dependencies> <!-- 从继承的父项目中继承依赖 --> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> </dependency> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <version>2.1</version> <configuration> <source>1.7</source> <target>1.7</target> </configuration> </plugin> </plugins> </build> </project>
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The end!
