Maven的继承以及import作用域

2022-10-29 18:23:44

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!

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