为什么要有多模块
单模块开发所面临的问题：
1.不同方面代码耦合，系统出现问题很难定位，可能在修正问题出现更多问题。
2.新入开发者介入成本高。
3.代码边界很模糊，多人合作不好配合。
所以出现了以maven管理的多模块应用，每个模块对应着一个pom.xml，之间通过继承和聚合相互关联。
多模块优点：
1.降低代码耦合度。
2.每个模块可以自解释，即可以只启动相应的模块。
3.多人协同边界定义清晰。
4.重点模块甚至可以抽象出来作为公共服务。
Spring中多模块配置
1.创建父工程,创建子模块
image.png
2.编辑父工程pom.xml
<?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指明继承关系，给出被继承的父项目的具体信息-->
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.4.5</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.example</groupId>
<artifactId>demo5</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>demo5</name>
<description>Demo project for Spring Boot</description>
<!--父模块打包类型必须为pom-->
<packaging>pom</packaging>
<properties>
<java.version>1.8</java.version>
</properties>
<!--模块声明：这里有很多子模块-->
<modules>
<module>model</module>
<module>web</module>
<module>server</module>
</modules>
<!--版本说明：这里统一管理依赖的版本-->
<dependencyManagement>
<dependencies>
<!--module-->
<dependency>
<groupId>com.example</groupId>
<artifactId>web</artifactId>
<version>0.0.1-SNAPSHOT</version>
</dependency>
<dependency>
<groupId>com.example</groupId>
<artifactId>server</artifactId>
<version>0.0.1-SNAPSHOT</version>
</dependency>
<dependency>
<groupId>com.example</groupId>
<artifactId>model</artifactId>
<version>0.0.1-SNAPSHOT</version>
</dependency>
</dependencies>
</dependencyManagement>
</project>
4.编辑子模块pom
model模块:运行数据库模型
<?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>
<artifactId>model</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>model</name>
<description>Demo project for Spring Boot</description>
<parent>
<groupId>com.example</groupId>
<artifactId>demo5</artifactId>
<version>0.0.1-SNAPSHOT</version>
</parent>
<dependencies>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
</dependency>
<dependency>
<groupId>org.mybatis.spring.boot</groupId>
<artifactId>mybatis-spring-boot-starter</artifactId>
<version>2.1.4</version>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.18.6</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.mybatis.generator</groupId>
<artifactId>mybatis-generator-maven-plugin</artifactId>
<version>1.3.7</version>
<configuration>
<configurationFile>
src/main/resources/mybatis-generator-config.xml
</configurationFile>
</configuration>
<dependencies>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.48</version>
</dependency>
</dependencies>
</plugin>
</plugins>
</build>
</project>
server模块：核心服务，依赖于model
<?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.example</groupId>
<artifactId>demo5</artifactId>
<version>0.0.1-SNAPSHOT</version>
</parent>
<artifactId>server</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>server</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>com.example</groupId>
<artifactId>model</artifactId>
</dependency>
</dependencies>
</project>
web模块：对外提供api查询接口,依赖于server
<?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.example</groupId>
<artifactId>demo5</artifactId>
<version>0.0.1-SNAPSHOT</version>
</parent>
<artifactId>web</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>web</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>com.example</groupId>
<artifactId>server</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<version>2.2.6.RELEASE</version>
</plugin>
</plugins>
</build>
</project>
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