I want to parse a docker-compose.yaml to Java classes using SnakeYaml.
Everything went well until I started working with “deployment” tag of Docker specification.
It has a “placement” tag, which has two properties: “constraints” and “preferences”. Each of them can be either a list or a map.

placement:
    constraints:
        disktype: ssd
        disktype2: hdd
    preferences:
        - datacenter=us-east

I am trying to parse this part of docker-compose to the following class:

@Getter
@Setter
public class DockerDeployPlacement {
    private Map<String,String> constraints;
    private Map<String,String> preferences;


    @Override
    public String toString() {
        return "DeployPlacementConfig{" +
               "constraints='" + constraints + ''' +
               ", preferences=" + preferences +
               '}';
    }
}

So, what I want is: if the “constraints” or “preferences” is a List – cast it to Map. The following logic must be applied only to the “placement” Node.

The whole YAML may look like this:

deploy:
    restart_policy:
       condition: on-failure
       delay: 5s
       max_attempts: 3
       window: 120s
    update_config:
       parallelism: 2
       delay: 10s
       order: stop-first
    rollback_config:
       parallelism: 2
       delay: 10s
       order: stop-first
       mode: replicated
       replicas: 2
       endpoint_mode: vip
       labels:
         com.example.description: "This label will appear on the web service"
    placement:
       constraints:
          disktype: ssd
          disktype2: hdd
    preferences:
          - datacenter=us-east