maven父子工程中的依赖引用的实现
作者：峰晨朴朴
本文主要介绍了Maven父子工程中的依赖引用的实现,包括<dependencyManagement>和<dependencies>两个标签的使用,以及父子pom文件的配置,感兴趣的可以了解一下
简述
项目越来越趋向模块化开发，使用maven构建工程，必然涉及到父子pom的关联，父pom文件的父级又会继承springboot项目，就这样在开发中踩坑不少，简单记录一下。
看问题之前先了解maven中的两个标签<dependencyManagement>和<dependencies>，明白的直接跳过。
maven标签
1、<dependencyManagement>这里其实是起到管理依赖jar版本号的作用，一般只会在项目的最顶层的pom.xml中使用到，所有子module如果想要使用到这里面声明的jar，只需要在子module中添加相应的groupId和artifactId即可，并不需要声明版本号，需要注意的是这里面只是声明一个依赖，并不是真实的下载jar，只有在子module中使用到，才会去下载依赖。
2、<dependencies>我们是这里引入了一个jar包之后，这里如果没有加上version版本号的话，那么maven就会去<dependencyManagement>里找对应groupId和artifactId的jar,如果有就继承他，如果没有就会报错，这时候其实在我们配置的本地仓库中会真实的下载对应的jar包，这时候所有的子module都会默认继承这里面所有声明的jar。
总的来说，就是在中声明依赖和版本号，该标签中的依赖不会被子模块继承，仅仅是声明，子pom中直接引入依赖，具体的版本号会在父子中去找。
父pom的packaging都是pom，子项目pom的packaging都是jar。关于在父子配置pom的引用有两种方案，这里以springboot项目为例说明问题。
第一种pom配置
我们希望在父pom中引入相关依赖，都记录在<dependencies>下，子模块直接继承父pom的依赖，在子模块中开发中就不必再去引入依赖，但在项目中有模块可能就是单一的工具包，它并不需要springboot的依赖，这时候启动就会冲突。可以这样解决，在父pom中定义springboot版本号，子模块作为项目启动的模块配置springboot插件依赖，普通的dao，serivce，common不必引入。如下配置文件，文件中只列举个别依赖包，重在说明问题：
父pom.xml配置：
<?xml version="1.0" encoding="UTF-8"?>
<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.demo</groupId>
<artifactId>demo-api</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>pom</packaging>
<modules>
<module>demo-web</module>
<module>demo-common</module>
<module>demo-service</module>
</modules>
<properties>
<spring-boot.version>2.1.8.RELEASE</spring-boot.version>
<java.version>1.8</java.version>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<fastjson.version>1.2.47</fastjson.version>
<pagehelper.version>5.1.6</pagehelper.version>
</properties>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-dependencies</artifactId>
<version>${spring-boot.version}</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<dependencies>
<!--这两个依赖都将被子模块继承-->
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>fastjson</artifactId>
<version>${fastjson.version}</version>
</dependency>
<dependency>
<groupId>com.github.pagehelper</groupId>
<artifactId>pagehelper</artifactId>
<version>${pagehelper.version}</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>8</source>
<target>8</target>
</configuration>
</plugin>
</plugins>
</build>
<profiles>
<profile>
<id>dev</id>
<properties>
<package.environment>dev</package.environment>
</properties>
<!-- 是否默认 true表示默认-->
<activation>
<activeByDefault>true</activeByDefault>
</activation>
</profile>
<profile>
<!-- 测试环境 -->
<id>test</id>
<properties>
<package.environment>test</package.environment>
</properties>
</profile>
<profile>
<!-- 生产环境 -->
<id>prod</id>
<properties>
<package.environment>prod</package.environment>
</properties>
</profile>
</profiles>
</project>
普通子模块pom.xml配置：
<?xml version="1.0" encoding="UTF-8"?>
<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">
<parent>
<artifactId>demo-api</artifactId>
<groupId>com.demo</groupId>
<version>1.0-SNAPSHOT</version>
</parent>
<modelVersion>4.0.0</modelVersion>
<groupId>com.demo.common</groupId>
<artifactId>demo-common</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>demo-common</name>
<description>demo-common project</description>
<packaging>jar</packaging>
</project>
启动类子模块pom.xml配置：
<?xml version="1.0" encoding="UTF-8"?>
<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>com.demo</groupId>
<artifactId>demo-api</artifactId>
<version>1.0-SNAPSHOT</version>
</parent>
<groupId>com.demo.web</groupId>
<artifactId>demo-web</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>demo-web</name>
<description>demo-web project</description>
<properties>
<java.version>1.8</java.version>
</properties>
<dependencies>
<!--引入子模块相关jar -->
<dependency>
<groupId>com.demo.common</groupId>
<artifactId>demo-common</artifactId>
<version>0.0.1-SNAPSHOT</version>
</dependency>
<dependency>
<groupId>com.myway.service</groupId>
<artifactId>share-read-service</artifactId>
<version>0.0.1-SNAPSHOT</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
<exclusions>
<exclusion>
<groupId>org.junit.vintage</groupId>
<artifactId>junit-vintage-engine</artifactId>
</exclusion>
</exclusions>
</dependency>
</dependencies>
<build>
<!--重要 如果不设置resource 会导致application.yaml中的@@找不到pom文件中的配置-->
<resources>
<resource>
<directory>src/main/resources</directory>
<filtering>true</filtering>
</resource>
</resources>
<plugins>
<!--仅在启动项目中引入springboot插件 -->
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<executions>
<execution>
<goals>
<goal>repackage</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>
第二种pom配置
将所有的依赖在父pom的中声明，子模块把需要的都引入一遍：
父pom.xml配置：
<?xml version="1.0" encoding="UTF-8"?>
<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.demo</groupId>
<artifactId>demo</artifactId>
<version>3.0.0</version>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<java.version>1.8</java.version>
<druid.version>1.1.14</druid.version>
<pagehelper.boot.version>1.2.5</pagehelper.boot.version>
<fastjson.version>1.2.70</fastjson.version>
</properties>
<!-- 依赖声明 -->
<dependencyManagement>
<dependencies>
<!-- SpringBoot的依赖配置-->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-dependencies</artifactId>
<version>2.1.8.RELEASE</version>
<type>pom</type>
<scope>import</scope>
</dependency>
<!--阿里数据库连接池 -->
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>druid-spring-boot-starter</artifactId>
<version>${druid.version}</version>
</dependency>
<!-- pagehelper 分页插件 -->
<dependency>
<groupId>com.github.pagehelper</groupId>
<artifactId>pagehelper-spring-boot-starter</artifactId>
<version>${pagehelper.boot.version}</version>
</dependency>
</dependencies>
</dependencyManagement>
<modules>
<module>demo-web</module>
<module>demo-common</module>
</modules>
<packaging>pom</packaging>
<dependencies>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.1</version>
<configuration>
<source>${java.version}</source>
<target>${java.version}</target>
<encoding>${project.build.sourceEncoding}</encoding>
</configuration>
</plugin>
</plugins>
</build>
<repositories>
<repository>
<id>public</id>
<name>aliyun nexus</name>
<url>http://maven.aliyun.com/nexus/content/groups/public/</url>
<releases>
<enabled>true</enabled>
</releases>
</repository>
</repositories>
<pluginRepositories>
<pluginRepository>
<id>public</id>
<name>aliyun nexus</name>
<url>http://maven.aliyun.com/nexus/content/groups/public/</url>
<releases>
<enabled>true</enabled>
</releases>
<snapshots>
<enabled>false</enabled>
</snapshots>
</pluginRepository>
</pluginRepositories>
<profiles>
<profile>
<id>dev</id>
<properties>
<package.environment>dev</package.environment>
</properties>
<!-- 是否默认 true表示默认-->
<activation>
<activeByDefault>true</activeByDefault>
</activation>
</profile>
<profile>
<!-- 测试环境 -->
<id>test</id>
<properties>
<package.environment>test</package.environment>
</properties>
</profile>
<profile>
<!-- 生产环境 -->
<id>prod</id>
<properties>
<package.environment>prod</package.environment>
</properties>
</profile>
</profiles>
</project>
普通子模块pom.xml配置：
<?xml version="1.0" encoding="UTF-8"?>
<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">
<parent>
<artifactId>demo</artifactId>
<groupId>com.demo</groupId>
<version>1.0.0</version>
</parent>
<modelVersion>4.0.0</modelVersion>
<artifactId>demo-system</artifactId>
<dependencies>
<dependency>
<groupId>com.demo</groupId>
<artifactId>demo-common</artifactId>
</dependency>
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>druid-spring-boot-starter</artifactId>
</dependency>
<dependency>
<groupId>com.github.pagehelper</groupId>
<artifactId>pagehelper-spring-boot-starter</artifactId>
</dependency>
</dependencies>
</project>
启动类子模块pom.xml配置：
<?xml version="1.0" encoding="UTF-8"?>
<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">
<parent>
<artifactId>demo</artifactId>
<groupId>com.demo</groupId>
<version>3.0.0</version>
</parent>
<modelVersion>4.0.0</modelVersion>
<packaging>jar</packaging>
<artifactId>demo-admin</artifactId>
<description>
web服务
</description>
<dependencies>
<dependency>
<artifactId>demo</artifactId>
<groupId>com.demo</groupId>
<version>1.0.0</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<version>2.1.8.RELEASE</version>
<configuration>
<fork>true</fork> <!-- 如果没有该配置，devtools不会生效 -->
</configuration>
<executions>
<execution>
<goals>
<goal>repackage</goal>
</goals>
</execution>
</executions>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-war-plugin</artifactId>
<version>3.0.0</version>
<configuration>
<failOnMissingWebXml>false</failOnMissingWebXml>
<warName>${project.artifactId}</warName>
</configuration>
</plugin>
</plugins>
</build>
</project>
以上是个人在构建项目中总结出来的，可供参考，重在理解。
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