What happen after "./gradlew {package}-rpm"

I am new to bigtop architecture, I would like to know how does bigtop know the real build command to launch for this specific package after ./gradlew {package}-rpm, I assume there must be some kind of configs define the real build command. (The package is a maven based project)

Thank you.

I'm not familiar with Bigtop, but I am familiar with Gradle. See here for the Gradle task definition that you're referring to: https://github.com/apache/bigtop/blob/2d6f3dd7b7241aa2191c9ebc5a502a1415932464/packages.gradle#L460

The command that the task will execute is given under the exec directive: rpmbuild <command>. command is an array of arguments defined just above that directive. Most of its arguments are derived from the config object, which is basically a nested map (like a JSON object) produced by Groovy's ConfigSlurper, which reads the input BOM file as if it were a Groovy file.

So:

1. "Slurp" the BOM configuation into the config object
2. For each "component" defined within the config configuration, produce a set of tasks (${package}-rpm and others)
3. When configuring the ${package}-rpm task, use the BOM configuration to derive the command arguments using the logic provided within the task closure
4. Upon execution, run rpmbuild with the aforementioned command arguments