How to create multi-modules project in Spring

In this article, we will learn how to configure multi-modules project in Spring with the support of Maven build tool. Using this approach makes our code better structure, easily maintain.

Let’s get started.

Create multi-modules project
Benefits and drawbacks
Some problems that we configure multi-modules projec
Deploy multi-module project
Wrapping up

Create multi-module project

Structure of multi-module project
- Parent project will configure with packing tag with pom. It will consist of version for all child projects, dependencies management, plugin management for building project.
- Child project main will contain static main method. It will have all dependencies that are child projects, and we will configure it to build jar file.
- Child project configuration will contain all configurations of program such as configurations of Spring MVC, or Webflux, and some beans …
- Child project shared will consist of some utility classes such as StringUtils, JsonUtils, CollectionUtils, …
- Child project webservice will contain all interfaces to communicate with client through Restful Api.
- Child project func-employee will contain implementation of controller, and other services, or repositories, or dao layer, and entities for mapping between objects and records in database.
We will create multi-module project with two ways:
- Use command line prompt with maven.
  - First, we have to create parent project with the packaging’s value is pom.
    mvn archetype:generate -DgroupId=com.manhpd -DartifactId=parent-project
    In pom.xml file of parent-project, we will fill it with <packaging>pom</packaging>. It means that parent-project will serve as a parent or an aggregator – it will not produce further artifacts.
    
    In parent-project, we will define all version of our packages for sub-modules.
  - Next, we will cd parent-project to create sub-modules.
    mvn archetype:generate -DgroupId=com.manhpd.pdMultiProj -DartifactId=main mvn archetype:generate -DgroupId=com.manhpd.pdMultiProj -DartifactId=configuration mvn archetype:generate -DgroupId=com.manhpd.pdMultiProj -DartifactId=shared mvn archetype:generate -DgroupId=com.manhpd.pdMultiProj -DartifactId=webservice mvn archetype:generate -DgroupId=com.manhpd.pdMultiProj -DartifactId=func-employee
    Open pom.xml file of parent-project, we will find that:
    <modules> <module>main</module> <module>configuration</module> <module>shared</module> <module>webservice</module> <module>func-employee</module> </modules>
  - Finally, we will configure for sub-modules with pom.xml file
    <parent> <groupId>com.manhpd</groupId> <artifactId>parent-project</artifactId> <version>1.0</version> </parent>
  - Note
    - All submodules can have only one parent.
- Use GUI with support of Intellij IDEA or Eclipse.
  - Create parent project
    
    Based on Maven, we will create parent project.
    
    Then, we have:
    
    Click Next button, we will have a parent project.
  - Create our submodules
    
    Similarly, we will continue to create our child modules.
    
    Open Project Structure of current parent-project, we have:
    
    Next, fill some desired information about child modules.
    
    Finally, we have main project with the following structure:
    
    As same as with other child modules, we have:
  - Refer sample:
    
    https://github.com/gamethapcam/J2EE/tree/master/src/libs/multi-modules-project/parent-project

Benefits and drawbacks

Benefits
- Reduce duplication.
- Share a vast amount of configuration with other modules.
- One single maven command to build all your modules at once.
- Conveniene to reuse code
Drawbacks
- understanding deeper project to work with it.

Some problems that we configure multi-modules project

In Intellij IDEA, usually cope with the error about “java: packages do not exists”
Create life cycle between dependencies

We are utilizing two modules that are dependency together. Solution for this problem is to remove uneccessary dependency in another module.

RestController/Controller/Service/Component was not called when each controller/service/component in one modules.

We should use @ComponentScan to solve this problem.

For example:

  @SpringBootApplication
  @ComponentScan(basePackages = { "com.manhpd.pdMultiProj.*" })
  public class MainApplication {
        
      private static Logger logger = (Logger) LogManager.getLogger(MainApplication.class);
        
      public static void main(String[] args) throws Exception {
          SpringApplication app = new SpringApplication(MainApplication.class);
          app.run(args);
      }
  }

Deploy multi-module project

There are some multiple ways to build multi-modules project into one fat jar file.

Use maven-shade-plugin

  <properties>
      <version.root>0.1</version.root>
      <start-class>com.manhpd.vcs-lol.Application</start-class>
      <application-name>vcs-lol</application-name>
  </properties>

  <build>
      <plugins>
          <plugin>
              <groupId>org.apache.maven.plugins</groupId>
              <artifactId>maven-shade-plugin</artifactId>
              <version>3.2.1</version>
              <executions>
                  <execution>
                      <id>create-fat-jar</id>
                      <phase>package</phase>
                      <goals>
                          <goal>shade</goal>
                      </goals>
                      <configuration>
                          <transformers>
                              <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                  <mainClass>${start-class}</mainClass>
                              </transformer>
                          </transformers>
                          <finalName>${application-name}</finalName>
                      </configuration>
                  </execution>
              </executions>
          </plugin>
      </plugins>
  </build>

We can refer this link.

Use spring-boot-maven-plugin

This plugins will be used in main module that in its pom.xml file, it has all declarations of the rest of modules.

  <properties>
      <version.root>0.1</version.root>
      <class.main>com.manhpd.vcs-lol.Application</class.main>
      <name.application>vcs-lol</name.application>
  </properties>

  <build>
      <finalName>${vcs-lol}</finalName>
      <plugins>
          <plugin>
              <groupId>org.springframework.boot</groupId>
              <artifactId>spring-boot-maven-plugin</artifactId>
              <executions>
                  <execution>
                      <goals>
                          <goal>repackage</goal>
                      </goals>
                      <configuration>
                          <mainClass>${class.main}</mainClass>
                      </configuration>
                  </execution>
              </executions>
          </plugin>
      </plugins>
  </build>

This way is working like a charm.

Running

 cd parent-project
 mvn clean install
 mvn exec:java -pl main -Dexec.mainClass=main.com.manhpd.pdMultiProj.MainApplication

Wrapping up

Understanding about the POM file and the meaning of them.
Create hierarchical project with hierarchical project, inheritance project, and dependency management.

Thanks for your reading.

Refer:

https://www.baeldung.com/maven-multi-module

https://books.sonatype.com/mvnex-book/reference/multimodule-sect-running-web.html

https://stackoverflow.com/questions/37133210/springboot-doesnt-recognize-restcontroller-from-another-module-in-multi-module

https://github.com/NABEEL-AHMED-JAMIL/pdftest/tree/master/multi-mudule

https://github.com/spring-projects/spring-boot/issues/12969

https://www.roytuts.com/spring-boot-multi-module-project/

http://www.miredot.com/docs/manual/general/project-organization/

https://stackoverflow.com/questions/52167511/controller-restcontroller-and-component-not-working-in-child-package-in-spr

https://stackoverflow.com/questions/37133210/springboot-doesnt-recognize-restcontroller-from-another-module-in-multi-module

https://www.mkyong.com/maven/maven-how-to-create-a-multi-module-project/