Maven构建多模块项目

首先，了解几个概念

• 1、<dependencyManagement> 简单说：就是声明，而不引入进项目，在子项目pom文件里引入该jar才会被引入

　　<dependencyManagement>
        <dependencies>
            <!-- spring cloud alibaba 依赖 -->
            <dependency>
                <groupId>com.alibaba.cloud</groupId>
                <artifactId>spring-cloud-alibaba-dependencies</artifactId>
                <version>${spring-cloud-alibaba.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

• 2、<dependencies> 简单说：就是使用该标签，不管子项目是否引入该jar都会自动引入

        <dependencies>
            <!-- spring cloud alibaba 依赖 -->
            <dependency>
                <groupId>com.alibaba.cloud</groupId>
                <artifactId>spring-cloud-alibaba-dependencies</artifactId>
                <version>${spring-cloud-alibaba.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>    

• 3、<modules> 多模块，当项目构建多模块时候配置子模块名称

　　<!-- 注意这一块的写法，xxx == name，没有网上一些其他博客说的../  -->
   <modules>
       <module>xxx</module>
   </modules>

接下来，就是贴代码

• 父工程

<?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>org.example</groupId>
    <artifactId>learn_nacos_cloud</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>
    <modules>
        <module>provider</module>
    </modules>

    <properties>
        <java.version>1.8</java.version>
        <spring-boot.version>2.4.4</spring-boot.version>
        <spring-cloud.version>2020.0.2</spring-cloud.version>
        <spring-cloud-alibaba.version>2020.0.RC1</spring-cloud-alibaba.version>
    </properties>

    <dependencyManagement>
        <dependencies>
            <!-- spring boot 依赖 -->
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-dependencies</artifactId>
                <version>${spring-boot.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
            <!-- spring cloud 依赖 -->
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
            <!-- spring cloud alibaba 依赖 -->
            <dependency>
                <groupId>com.alibaba.cloud</groupId>
                <artifactId>spring-cloud-alibaba-dependencies</artifactId>
                <version>${spring-cloud-alibaba.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

</project>

• 子工程

<?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>
    <parent>
        <artifactId>learn_nacos_cloud</artifactId>
        <groupId>org.example</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>

    <name>provider</name>
    <groupId>org.example</groupId>
    <artifactId>provider</artifactId>
    <version>${parent.version}</version>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
        </dependency>
    </dependencies>

    <properties>
        <maven.compiler.source>14</maven.compiler.source>
        <maven.compiler.target>14</maven.compiler.target>
    </properties>

</project>

结尾呢，说一下注意事项

• 就是 <modules> 网上各种各样的写法
• 然后就是子模块只要写对了父以下内容

    <parent>
        <artifactId>learn_nacos_cloud</artifactId>
        <groupId>org.example</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>

• 然后 也是今天最困扰我的一点，就是子模块所引入的jar，一定一定要是你父模块引入的。否则直接会报如下异常

这个异常在1.5秒左右直接就报出来，而且清空了console，让人很不好定位问题。