How to develop a Maven Multi-module application using the Spring Boot framework

Question

I have a maven multi-module Java project that runs perfectly, until I try to include the Spring Boot framework. The main module, called core , gets called OK, but all the rest are unable to implement the interface I declared in Core.java .

This error gets thrown:

[ERROR] /F:/mvnmodularapp/module1/src/main/java/service/impl/ModuleServiceImpl.java:[12,30] cannot find symbol
[ERROR] symbol: class Service

[ERROR] /F:/mvnmodularapp/module1/src/main/java/service/impl/ModuleServiceImpl.java:[13,5] method does not override or implement a method from a supertype

---

The project structure:

mvnmodularapp/
             /pom
mvnmodularapp/core/
             /src
             /target/core-1.0-SNAPSHOT.jar
mvnmodularapp/module1
             /src
             /target/module1-1.0-SNAPSHOT.jar

---

THe file/directory structure:

core/src/java/service/
                    Service.java

core/src/java/service/impl
                        CoreServiceImpl.java

module1/src/java/service/impl
                        ModuleServiceImpl.java

---

Service.java

public interface Service {

    String getName();
}

CoreServiceImpl.java in core

@Service
public class ServiceImpl implements Service {
    @Override
    public String getName() {
        return "Hi. You called me from ServiceImpl in Core";
    }
}

ModuleServiceImpl.java in module1

@Service
public class ModuleServiceImpl implements Service {
    @Override
    public String getName() {
        return "Hi. You called me from ModuleServiceImpl in module1, but I can\'t pick up right now. Sorry";
    }
}

---

THE POMS

mvnmodularapp 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.mvnmodularapp</groupId>
    <artifactId>mvnmodularapp</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>

    <modules>
        <module>core</module>
        <module>module1</module>
    </modules>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.4.3.RELEASE</version>
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>

</project>

core 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">

    <parent>
        <artifactId>mvnmodularapp</artifactId>
        <groupId>com.mvnmodularapp</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>core</artifactId>
    <version>1.0-SNAPSHOT</version>

    <name>Core</name>
    <description>SudenGut application</description>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <start-class>main</start-class>
        <java.version>1.8</java.version>
        <tomcat.version>8.0.24</tomcat.version>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <!--- this will not be enough to provide a cool app :) -->
    </dependencies>

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

</project>

module1 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">
    <parent>
        <artifactId>mvnmodularapp</artifactId>
        <groupId>com.mvnmodularapp</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>module1</artifactId>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <start-class>baseview.impl.BaseViewImpl.ModuleServiceImpl</start-class>
        <java.version>1.8</java.version>
        <tomcat.version>8.0.24</tomcat.version>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <!--- this will not be enough to provide a cool app :) -->
        <dependency>
            <groupId>com.mvnmodularapp</groupId>
            <artifactId>core</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
    </dependencies>

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

</project>

Answer 1

Dependencies between modules are correctly declared but you have one thing that is not configured as required.
I am not sure it will solve your problem but it could.

You declare in each module :

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

It should be required only for the module which bootstraps the Spring Boot application.
If you want have multiple web applications in the same Spring Boot container, you could read this question .

As you say that it works before adding Spring Boot I think that the problem should be solved with previous recommandation.
But if it is not enough, below are other guessworks which could be the cause of the compilation error. I rely on this error message :

[ERROR] /F:/mvnmodularapp/module1/src/main/java/service/impl/ModuleServiceImpl.java:[12,30] cannot find symbol [ERROR] symbol: class Service

• The Service class is not imported in ModuleServiceImpl .
  If I rely on what you write in your question, you should add : import service.Service in the imports of ModuleServiceImpl .
  

• The core module doesn't create a JAR with the service.Service class.
  So, importing it doesn't solve the problem of the module1 module.
  You should perform a mvn clean install from the core module and check that the jar contains the compiled class : service.Service in the good package.