Java Jackson deserialize null field to default empty list in POJO

Lombok's @Builder is not a direct problem here, cause Jackson does not use it for deserialization. However, Jackson is using non-default constructor with args, if it is available, for object instantiation. Otherwise it is using non-arg constructor. When you use @AllArgsConstructor on ResponsePOJO, Jackson takes created constructor which looks like this:

public ResponsePOJO(List<Object> list1, List<Object> list2, List<Object> list3, List<Object> list4) {
    this.list1 = list1;
    this.list2 = list2;
    this.list3 = list3;
    this.list4 = list4;
}

And when this constructor is invoked, your default value is discarded and null is assigned for non-existent fields in JSON.

While @Builder requires all arguments constructor, you have few ways to fix the issue:

1. Not use @Builder and remove @AllArgsConstructor - sometimes you may not need any of these, but it depends on your case
2. Remove @AllArgsConstructor and create custom builder, which is not using all arguments constructor inside, but the no-arg one.

3. Use @Builder and create custom all arguments constructor similar to this one:

   public ResponsePOJO(List<Object> list1, List<Object> list2, List<Object> list3, List<Object> list4) {
       this.list1 = list1 == null ? Lists.newArrayList() : list1;
       this.list2 = list2 == null ? Lists.newArrayList() : list2;
       this.list3 = list3 == null ? Lists.newArrayList() : list3;
       this.list4 = list4 == null ? Lists.newArrayList() : list4;
   }
   

   Here Jackson would still invoke all arguments constructor above, but if some field does not exist OR exists and is null (this may have downstream impact on your business logic if in some cases you may expect null values, e.g. validation against nullity), it will always assign empty list.

The problem is that you're also adding @Builder. The initializer is moved to the builder, as you don't want to run the code twice.

Recent versions (1.16.16+) of lombok have the @Builder.Default that you can use to influence that behavior.

You can instruct Jackson to use the builder instead, and make your objects immutable. Builder is meant for immutable objects.

Disclosure: I am a lombok developer.

I ran into a similar issue deserializing a JSON object using Jackson (com.fasterxml.jackson) and Lombok's @Builder annotation. I was able to resolve this issue by creating an empty Builder class annotated with @JsonPOJOBuilder inside the class and then adding a @JsonDeserialize with a reference to the empty class. You can find more info here

For example,

@Getter
@ToString
@NoArgsConstructor
@Builder
@AllArgsConstructor
@EqualsAndHashCode
@JsonIgnoreProperties(ignoreUnknown = true)
@JsonDeserialize(builder = ResponsePOJO.TypeBuilder.class)
public class ResponsePOJO {
    @JsonPOJOBuilder(withPrefix = "")
    @JsonIgnoreProperties(ModelUtils.TYPE_INFO_PROPERTY)

   public static class TypeBuilder{}//Empty builder class
                                    //Needed just to apply annotations
                                    //Lombok will fill it in later.

    @JsonProperty("list-one")
    private List<Object> list1 = Lists.newArrayList;
    @JsonProperty("list-two")
    private List<Object> list2 = Lists.newArrayList;
    @JsonProperty("list-three")
    private List<Object> list3 = Lists.newArrayList;
    @JsonProperty("list-four")
    private List<Object> list4 = Lists.newArrayList;
}