多modules的好处？

• 首先是实现了各个模块之间的解耦，模块可以单独调用，性能会更好
• 多module的层次更明显，使项目结构更清晰，便于管理，出现问题时也更好排查原因
• 逼格更高

层级关系

实际上就是MVC

• dao层依赖model
• service层依赖dao、model
• web层依赖dao、model、service

多模块项目创建

首先使用SpringBoot initalizr创建一个Maven工程，并删除父项目中的src目录，只留一个pom.xml文件

注意：父项目中无需打包，可设置packaging为pom，或者不打包

<?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>

    <!--项目基本信息-->
    <groupId>com.qd</groupId>
    <artifactId>magina</artifactId>
    <packaging>pom</packaging>
    <version>0.0.1-SNAPSHOT</version>

    <name>magina</name>
    <description>Demo project for Spring Boot</description>

    <!--声明子项目-->
    <modules>
        <module>magina-dao</module>
        <module>magina-service</module>
        <module>magina-model</module>
        <module>magina-web</module>
    </modules>


    <!--这里作为聚合工程的父工程-->
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.1.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <!--这里继承SpringBoot提供的父工程-->
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>


    <!--项目依赖-->
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

		<!--fastjson-->
            <dependency>
                <groupId>com.alibaba</groupId>
                <artifactId>fastjson</artifactId>
                <version>1.2.41</version>
            </dependency>

            <!--mybatis-plus-->
            <dependency>
                <groupId>com.baomidou</groupId>
                <artifactId>mybatis-plus</artifactId>
                <version>2.1.9</version>
            </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

依次在项目上创建子模块

• magina-model
• magina-dao
• magina-service
• magina-web

此时父pom中会自动生成子模块依赖，子模块的parent也会使用顶层的父项目

<modules>
        <module>magina-dao</module>
        <module>magina-service</module>
        <module>magina-model</module>
        <module>magina-web</module>
    </modules>

完整的项目结构如下

子项目pom文件如下，此处举个栗子dao的pom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">

    <!--继承父项目-->
    <parent>
        <artifactId>magina</artifactId>
        <groupId>com.qd</groupId>
        <version>0.0.1-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>magina-dao</artifactId>
    <packaging>jar</packaging>

    <dependencies>
        <dependency>
            <groupId>com.qd</groupId>
            <artifactId>magina-model</artifactId>
            <version>0.0.1-SNAPSHOT</version>
        </dependency>

        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
        </dependency>

        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus</artifactId>
        </dependency>
    </dependencies>

</project>

子项目中packaging需要打成jar包