How is the maven version specified in Spring Boot Starters?

Question

I'm read the reference but I don't understand how versionId is set in the dependency. For example the MongoDB starter specifies

<dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.mongodb</groupId>
            <artifactId>mongodb-driver</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.data</groupId>
            <artifactId>spring-data-mongodb</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>org.mongodb</groupId>
                    <artifactId>mongo-java-driver</artifactId>
                </exclusion>
                <exclusion>
                    <groupId>org.slf4j</groupId>
                    <artifactId>jcl-over-slf4j</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>

But the version tag is missing. How is the version of mongodb-driver determined when using these starts?

Answer 1

The versions of the starter atrifacts are managed in the starter parent. For example, if you have this in your POM:

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.0.2.RELEASE</version>
</parent>

Then any boot starter dependency you reference will have version 2.0.2.RELEASE, unless you override the default and provide your own version for some reason.