Spring Boot Actuator displays build-related information if a META-INF/build-info.properties file is present. The build-info goal generates such file with the coordinates of the project and the build time. It also allows you to add an arbitrary number of additional properties:

<project>
  ...
  <build>
    ...
    <plugins>
      ...
      <plugin>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-maven-plugin</artifactId>
        <version>2.0.9.BUILD-SNAPSHOT</version>
        <executions>
          <execution>
            <goals>
              <goal>build-info</goal>
            </goals>
            <configuration>
              <additionalProperties>
                <encoding.source>UTF-8</encoding.source>
                <encoding.reporting>UTF-8</encoding.reporting>
                <java.source>${maven.compiler.source}</java.source>
                <java.target>${maven.compiler.target}</java.target>
              </additionalProperties>
            </configuration>
          </execution>
        </executions>
        ...
      </plugin>
      ...
    </plugins>
    ...
  </build>
  ...
</project>

This configuration will generate a build-info.properties at the expected location with four additional keys. Note that maven.compiler.source and maven.compiler.target are expected to be regular properties available in the project. They will be interpolated as you would expect.