JAVA搞不清楚系列 - Spring Boot Multi Module Porject

第一次碰到Multi Module其實應該是在做gRPC的專案的時候，後來才又重新認真研究了一下。
Spring Boot的Multi Module 可以幫助專案規劃分module，重複使用POM，以免引入變得過於龐大，且不用每次都構建整個專案，並且使得針對某個模組的特殊控制更為方便。

Gitlab連結

https://gitlab.com/jam68ty/spring-boot-multi-modules-semgrep

流程總覽

1. 建立一個母moudule以及兩個子module
2. 重構專案結構、產生jar檔
3. 母module引入子moudule
4. 寫一些測試的Service, Controller
5. 此時應該要可以透過母module去控管整個專案共同需要的POM，而個別子module需要的dependency則在該module中引入即可

實作詳解

1. 利用Maven Quickstart Archetype建立一個Parent Module

   mvn archetype:generate -DarchetypeGroupId=org.apache.maven.archetypes -DarchetypeArtifactId=maven-archetype-quickstart -DarchetypeVersion=1.4

2. 用Spring Initializr建立兩個Child Modules，並把這兩個專案都移到Parent Module下
   a. jdjcore: 不引入任何dependency
   b. jdjweb: 引入Spring-web

3. 完成後先mvn clean install 母Module
   

4. 修改Parent Module的POM，引入兩個子Module

   <?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.test</groupId>
   <artifactId>multi-module-project</artifactId>
   <version>1.0-SNAPSHOT</version>
   <!--  更改packaging的類型為pom-->
   <packaging>pom</packaging>   
   <name>multi-module-project</name>
   
   <properties>
       <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
       <maven.compiler.source>1.8</maven.compiler.source>
       <maven.compiler.target>1.8</maven.compiler.target>
       <java-version>1.8</java-version>
   </properties>
   
   <!--  引入子modules-->
   <modules>
       <module>jdj-core</module>
       <module>jdj-web</module>
   </modules>
   
   <dependencies>
       <dependency>
       <groupId>org.springframework.boot</groupId>
       <artifactId>spring-boot-starter-test</artifactId>
       <version>2.3.6.RELEASE</version>
       <scope>test</scope>
       </dependency>
       <dependency>
       <groupId>org.springframework.boot</groupId>
       <artifactId>spring-boot-starter</artifactId>
       <version>2.3.6.RELEASE</version>
       </dependency>
   </dependencies>
   </project>

5. 修改Child Module - jdjcore (包含Entity, DAO, Service)

• POM

  <?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.test</groupId>
  <artifactId>multi-module-project</artifactId>
  <version>1.0-SNAPSHOT</version>
  <!--  更改packaging的類型為pom-->
  <packaging>pom</packaging>   
  <name>multi-module-project</name>
  
  <properties>
      <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
      <maven.compiler.source>1.8</maven.compiler.source>
      <maven.compiler.target>1.8</maven.compiler.target>
      <java-version>1.8</java-version>
  </properties>
  
  <!--  引入子modules-->
  <modules>
      <module>jdj-core</module>
      <module>jdj-web</module>
  </modules>
  
  <dependencies>
      <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-test</artifactId>
      <version>2.3.6.RELEASE</version>
      <scope>test</scope>
      </dependency>
      <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter</artifactId>
      <version>2.3.6.RELEASE</version>
      </dependency>
  </dependencies>
  </project>

• DAO: com.test.jdjcore.dao.CustomerRepository

  package com.test.jdjcore.dao;
  
  import com.test.jdjcore.entity.Customer;
  
  public interface CustomerRepository {
      Customer getCustomerById(int id);
  }

• Service: com.test.jdjcore.service.CustomerService

  package com.test.jdjcore.service;
  
  import com.test.jdjcore.dao.CustomerRepository;
  import com.test.jdjcore.entity.Customer;
  import org.springframework.stereotype.Service;
  
  @Service("customerService")
  public class CustomerService implements CustomerRepository{
  
      @Override
      public Customer getCustomerById(int id) {
          return new Customer(id, "name", "email");
      }
  }

• 把JdjCoreApplication的@SpringBootApplication註解掉，並把main的內容也刪除

1. 修改Child Module - jdjweb (包含Controller)

• POM

  <?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>
  <!--  引入母modules-->
      <parent>
          <groupId>com.test</groupId>
          <artifactId>multi-module-project</artifactId>
          <version>1.0-SNAPSHOT</version>
      </parent>
      <artifactId>jdj-web</artifactId>
      <version>0.0.1-SNAPSHOT</version>
      <name>jdj-web</name>
      <description>Demo project for Spring Boot</description>
      <properties>
          <java.version>1.8</java.version>
      </properties>
      <dependencies>
          <dependency>
              <groupId>org.springframework.boot</groupId>
              <artifactId>spring-boot-starter-web</artifactId>
              <version>2.6.4</version>
          </dependency>
  
          <dependency>
              <groupId>org.springframework.boot</groupId>
              <artifactId>spring-boot-starter-test</artifactId>
              <version>2.6.4</version>
              <scope>test</scope>
          </dependency>
          <dependency>
          <groupId>com.test</groupId>
          <artifactId>jdj-core</artifactId>
              <version>0.0.1-SNAPSHOT</version>
          </dependency>
      </dependencies>
  
      <build>
          <plugins>
              <plugin>
                  <groupId>org.springframework.boot</groupId>
                  <artifactId>spring-boot-maven-plugin</artifactId>
              </plugin>
          </plugins>
          <finalName>javadev-web</finalName>
      </build>
  
  </project>

• Controller: com.test.jdjweb.controller.CustomerController

  package com.test.jdjweb.controller;
  
  import com.test.jdjcore.dao.CustomerRepository;
  import com.test.jdjcore.entity.Customer;
  import com.test.jdjcore.service.CustomerService;
  import org.springframework.beans.factory.annotation.Autowired;
  import org.springframework.web.bind.annotation.GetMapping;
  import org.springframework.web.bind.annotation.PathVariable;
  import org.springframework.web.bind.annotation.RequestMapping;
  import org.springframework.web.bind.annotation.RestController;
  
  @RestController
  @RequestMapping("")
  public class CustomerController {
  
      @Autowired
      CustomerService customerService;
  
      @GetMapping("/customer/{id}")
      public Customer getCustomer(@PathVariable int id){
          return customerService.getCustomerById(id);
      }
  
  }

  由於Multi-modules，@Autowierd可能會出錯，此時需要在JdjWebApplication.java加上@ComponentScan({”com.test.jdjcore”, “com.test.jdjweb”})

結果

1. Start Application: 對整個專案mvn clean install → mvn spring-boot:run jdj-web
   
2. Test: http://localhost:8080/customer/1