1. GitHub Releases or IntelliJ IDEs Plugin Marketplace DartMappable page download plugin
2. Open in the IDE Setting -> Plugins, right click setting icon ⚙️ -> Install Plugin from Disk... selected you download file.

Json to dart data classes are provided, and dart files ending in entity are provided to generate dart class factory for use.

Right click on package -> New -> Json To DartMappable　And Then you will know how to use.

If you change the fields in the class, right click on package -> Flutter Command -> Flutter Run Build Runner, shortcut key is changed to Alt + r.

Don't forget to set up dart_mappable into your project : https://pub.dev/packages/dart_mappable
Add into your pubspec.yaml

dependencies:
  dart_mappable: ^3.0.0  
dev_dependencies: 
  build_runner: ^2.1.0
  dart_mappable_builder: ^3.0.2

Or Run Terminal

flutter pub add dart_mappable
flutter pub add build_runner --dev
flutter pub add dart_mappable_builder --dev

Open in the IDE Setting -> Tools -> DartMappable Settings, selected json_serializable.
Don't forget to set up json_serializable into your project : https://pub.dev/packages/json_serializable
Add into your pubspec.yaml

dependencies:
  json_annotation: ^4.8.0
dev_dependencies:
  build_runner: ^2.3.3
  json_serializable: ^6.6.0

Or Run Terminal

flutter pub add json_annotation
flutter pub add build_runner --dev
flutter pub add json_serializable --dev