Environment variables can be specified using the environmentVariables attribute. The following sets the 'ENV1', 'ENV2', 'ENV3', 'ENV4' env variables:

<project>
  ...
  <build>
    ...
    <plugins>
      ...
      <plugin>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-maven-plugin</artifactId>
        <version>2.2.6.RELEASE</version>
        <configuration>
            <environmentVariables>
                <ENV1>5000</ENV1>
                <ENV2>Some Text</ENV2>
                <ENV3/>
                <ENV4></ENV4>
            </environmentVariables>
        </configuration>
        ...
      </plugin>
      ...
    </plugins>
    ...
  </build>
  ...
</project>

If the value is empty or not defined (i.e. <MY_ENV/>), the env variable is set with an empty String as the value. Maven trims values specified in the pom so it is not possible to specify an env variable which needs to start or end with a space.

Any String typed Maven variable can be passed as system properties. Any attempt to pass any other Maven variable type (e.g. a List or a URL variable) will cause the variable expression to be passed literally (unevaluated).

Environment variables defined this way take precedence over existing values.