Spring Boot (kotlin) circular dependency

Question

I created the Spring Boot project with the Spring Boot Initializer. I have added Core, Data and Service modules. Now I see a warning after the build and in IntelliJ Project Structure: Project exampleapi: there is circular dependency between 'service' module, 'data' module, 'core' module.

Here is my 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>
<packaging>jar</packaging>
<modules>
    <module>service</module>
    <module>data</module>
    <module>core</module>
</modules>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.6.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <groupId>com.mjana</groupId>
    <artifactId>exampleapi</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>exampleapi</name>
    <description>Example Api</description>

    <properties>
        <java.version>11</java.version>
        <kotlin.version>1.3.71</kotlin.version>
    </properties>

    <repositories>
        <repository>
            <id>exposed</id>
            <name>exposed</name>
            <url>https://dl.bintray.com/kotlin/exposed</url>
        </repository>
    </repositories>

    <dependencies>
        <!--Modules-->
        <dependency>
            <groupId>com.mjana</groupId>
            <artifactId>core</artifactId>
            <version>0.0.1-SNAPSHOT</version>
        </dependency>
        <dependency>
            <groupId>com.mjana</groupId>
            <artifactId>service</artifactId>
            <version>0.0.1-SNAPSHOT</version>
        </dependency>
        <dependency>
            <groupId>com.mjana</groupId>
            <artifactId>data</artifactId>
            <version>0.0.1-SNAPSHOT</version>
        </dependency>

        <!--Data-->
        <dependency>
            <groupId>com.microsoft.sqlserver</groupId>
            <artifactId>mssql-jdbc</artifactId>
            <version>8.2.1.jre11</version>
        </dependency>
        <dependency>
            <groupId>org.jetbrains.exposed</groupId>
            <artifactId>exposed-spring-boot-starter</artifactId>
            <version>0.22.1</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jdbc</artifactId>
            <version>2.2.6.RELEASE</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.module</groupId>
            <artifactId>jackson-module-kotlin</artifactId>
        </dependency>
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-reflect</artifactId>
        </dependency>
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-stdlib-jdk8</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>

    <build>
        <sourceDirectory>${project.basedir}/src/main/kotlin</sourceDirectory>
        <testSourceDirectory>${project.basedir}/src/test/kotlin</testSourceDirectory>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
            <plugin>
                <groupId>org.jetbrains.kotlin</groupId>
                <artifactId>kotlin-maven-plugin</artifactId>
                <configuration>
                    <args>
                        <arg>-Xjsr305=strict</arg>
                    </args>
                    <compilerPlugins>
                        <plugin>spring</plugin>
                    </compilerPlugins>
                </configuration>
                <dependencies>
                    <dependency>
                        <groupId>org.jetbrains.kotlin</groupId>
                        <artifactId>kotlin-maven-allopen</artifactId>
                        <version>${kotlin.version}</version>
                    </dependency>
                </dependencies>
            </plugin>
        </plugins>
    </build>

</project>

And the pom of each module is the same except for artifactId:

    <?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>exampleapi</artifactId>
        <groupId>com.mjana</groupId>
        <version>0.0.1-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>service</artifactId>
    <packaging>jar</packaging>
</project>

Answer 1

You get circular dependency error b/c each of the child modules inherits the parent's configuration where you declare dependencies on the childs. Hence the circular dependency error.

You need to remove parent reference from each of the childs for them not to inherit this dependency configuration.