Non entity variables: Fields in a "Serializable" class should either be transient or serializable

Question

Fields in a "Serializable" class should either be transient or serializable is possible to fix any entity/class is used in another class, but it occurs when List/ Map is declared in a dto class which can't be even made as transient as well. please let me know how to fix this.

Ex:

public class CustomMetadataDTO implements Serializable {

private UUID id;

private Map<String, Object> metadata = new HashMap<>();

private UUID fieldGroupId;

private Integer order;


public CustomMetadataDTO(Map<String, Object> metadata, Integer order) {
    this.metadata = metadata;
    this.order = order;
}

public CustomMetadataDTO() {
}}

for below line I get the sonarqube issue as critical

private Map<String, Object> metadata = new HashMap<>();

Answer 1

HashMap is serializable but Map is not as it does not implement Serializable interface. You can try using HashMap itself while declaring (not recommended).

private HashMap<String, Object> metadata = new HashMap<>();