Spring Maven project structure pom.xml

Question

I'd like to get help in setting up a multi-module Maven project using Spring Boot.

Correct me if I'm wrong but I've read that Spring-Boot reads the start main Application (Annotated with @SpringBootApplication and ran with SpringApplication.run ) and finds the necessary classes through reflection. Which means that it first accesses the start class and then proceeds to find the controllers, models, repositories. If so, how do I set up the dependency in the pom.xml of each module if I had a project structure like this:

app
--src
--pom.xml

core
--pom.xml

--models
----/pom.xml

--controllers
----/pom.xml

--repositories
----/pom.xml

pom.xml

Answer 1

Please have a look complete guide how to create multi module project in spring boot.

https://spring.io/guides/gs/multi-module/

Answer 2

Spring boot will component scan from the package of the class annotated with @SpringBootApplication . Component scannign means that it is looking through the classes under that package recursively, analyzing annotations, and wiring up anything it recognizes. This can include controllers, simple variables with @Value annotations, members with @Autowired , and a host of other things.

You can actually jump into the source for the @SpringBootApplication annotation and see that it expands to numerous other annotations, @ComponentScan being one of them.

If all of your modules are in a sub-hierarchy package wise from there, then they will be scanned properly anyway. Often though, sub-modules will be in a slightly different package hierarchy. In this case, you can explicitly specify @ComponentScan() in your code and inside the () you can list the base packages to component scan from.

Whether or not its a sub-module doesn't matter much at this point; its just like scanning classes in any other library you're including.

General Advice

Also, just FYI - Multi module projects can get a little hard to manage (speaking from numerous separate experiences). They can be very good if used properly though. If you're a beginner to Maven though, it may be wiser to keep separte, well-defined projects with a proper release cycle and just import them as normal dependencies.

So, I'm not for or against them, but just make sure you understand them well going in :).

Answer 3

I have a GitHub project where I configured a multimodule maven project:

https://github.com/cristianprofile/spring-boot-mvc-complete-example

This is Example project maven module structure:

 Spring mvc rest maven module ---> service maven module  ---> repository maven module

The main module should be configured like this (Spring mvc rest layer):

@SpringBootConfiguration
@EnableAutoConfiguration
//spring mvc module auto scan only its package
@ComponentScan(basePackageClasses = HelloWorldController.class)
//It needs Service bean so it will import ConfigurationService.class from
// Service maven module
@Import({ConfigurationService.class})

Complete class:

https://github.com/cristianprofile/spring-boot-mvc-complete-example/blob/develop/spring-boot-mvc-rest/src/main/java/com/mylab/cromero/controller/Application.java

It will only scan its package :

HelloWorldController.class  -->  com.mylab.cromero.controller;

This Rest layer use a service maven module so it is necessary to add dependency:

    <dependency>
        <groupId>com.mylab.cromero.core</groupId>
        <artifactId>mylab-core-service-impl</artifactId>
        <version>0.0.2-SNAPSHOT</version>
    </dependency>

Complete pom file:

https://github.com/cristianprofile/spring-boot-mvc-complete-example/blob/develop/spring-boot-mvc-rest/pom.xml#L16

ConfigurationService.class from service maven module autoscan its packages and it will import ConfigurationRepository.class (Repository maven module)

@Configuration
//It needs repository's bean so it will import ConfigurationRepository.class from
// Repository maven module
@Import(ConfigurationRepository.class)
//service layer module auto scan only its package
@ComponentScan(basePackageClasses = ConfigurationService.class)
public class ConfigurationService {

}

Complete Service maven module code:

https://github.com/cristianprofile/spring-boot-mvc-complete-example/blob/develop/mylab-core/mylab-core-service-impl/src/main/java/com/mylab/cromero/service/ConfigurationService.java#L12

Service maven module layer has a dependency with maven repository module:

https://github.com/cristianprofile/spring-boot-mvc-complete-example/blob/develop/mylab-core/mylab-core-service-impl/pom.xml#L38

Repository module will auto configure jpa and domain classed:

@Configuration
@EnableJpaRepositories(basePackages = "com.mylab.cromero.repository")
@EntityScan(basePackageClasses=Base.class)
@ComponentScan(basePackageClasses = BaseRepository.class)
public class ConfigurationRepository {

}