Object type remains as LinkedHashMap after assignment

I have the following JSON data being fetched from an external file source.

{
    .... More complicated structures within this JSON format above but I only care about the following
    "feature": {
        "100": {
            "DATA1": [
                {
                    "header": "head1",
                    "someId": "123"
                }
            ]
        }
    }
}

I am trying to capture the following portion as List < Data >

"DATA1": [
    {
        "header": "head1",
        "someId": "123"
    }
]

but unable to do so. Getting following error:

> Cannot cast LinkedHashMap to List.

Method which fetched the data and try to assign it to List< Data >

private void getData(){
    AllDataFromFile all = someFetchAPI(); // Got every JSON data in the file. 

    // capturing the portion that I want which I do get. 
    Map<String, Map<String,Object>> feature = all.getFeature(); 
    Map<String, Object> allData = feature.get("100");
    List<Data> dataList = allData.get("DATA1");
}

No compilation nor run time errors from above but dataList is not a List of Data.

Instead it is a List of LinkedHashMap when I see in debug mode. Why?
And how can I turn this into a List of Data instead?

Since it doesn't map as a List< Data >, I am unable to perform operations such as follows.

dataList.get(0).getHeader(). 

Unable to cast it either and getting same error:

> Cannot cast LinkedHashMap to List.

Please advice. Thanks.

AllDataFromFile class

@Getter
@Setter
@JsonInclude(Include.NON_NULL)
public class AllDataFromFile {
	private Map<String, Map<String,Object>> feature;
}

Data class

@JsonInclude(Include.NON_NULL)
public class Data implements Comparable<Data>, Cloneable{	
	private String header;
    private String someId;

    @Override
	public int compareTo(Data o) {
        int result = // some logic
		return result;
	}	
}

EDIT:

This is data format inside List<Data>

result = {ArrayList@18590} size = 1
  0 = {LinkedHashMap@18593} size = 2
    "header" -> "header1"
    "someId" -> "id1"

Getting following error when I try to match the Object's value to be more specific as follows.

private Map<String, Map<String, List<Data>>> feature;

Able to go back to getting LinkedHashMap (no use, back to Square one) if I go for the following:

private Map<String, Map<String, List>> feature;

Error:

> Could not read JSON: Class java.util.LinkedHashMap not subtype of
> [simple type, class com.a.a.a.a.a.Data] (through reference chain:
> com.b.b.b.b.b.b.AllDataFromFile["feature"]->java.util.LinkedHashMap["100"]->java.util.LinkedHashMap["DATA1"]->java.util.ArrayList[0])

Jackson uses reflection to determine what type it needs to deserialize too.

But starting from AllDataFromFile, it cannot determine that the content is actually a List of Data objects, so it falls back to default Lists (ArrayList) and Maps(LinkedHashMap).

I think if you provide more information in the type declaration, jackson might figure it out:

public class AllDataFromFile {
    private Map<String, Map<String, List<Data>>> feature;
}