Remove empty JSON objects from an array in Jackson serialization

Question

I have a List in a Java Pojo class. That list contains some MyChildPojo objects which are not null but can have properties with null values. Example:

MyChildPojo obj1 = new MyChildPojo();
MyChildPojo obj2 = new MyChildPojo();

I have added @JsonInclude(JsonInclude.Include.NON_EMPTY) on my MyChildPojo class so null properties will not be added while serializing the object. Now my final serialized output for the List object is:

[
  {}, {}
]

I want to remove the complete List object in this case. I have tried by adding @JsonInclude(JsonInclude.Include.NON_EMPTY) and @JsonInclude(value = Include.NON_EMPTY, content = Include.NON_EMPTY) on the List object but still getting the same output.

I can only use annotation in my case. Is there any possible way to do this?

Does this answer your question? Don't return property when it's an empty list with jackson. You said "only annotations", but if you can add an annotation, I think you should also be able to set the WRITE_EMPTY_JSON_ARRAYS property. — andrewJames
– andrewJames, Commented May 27, 2020 at 21:43
Thanks for suggesting this. It is very similar to my use case. But in my case it is [{}, {}] and not []. So it will not work. — ankur_rajput
– ankur_rajput, Commented May 28, 2020 at 13:36

stackguy · Accepted Answer · 2020-05-28 00:10:23Z

You can use annotations with custom filter to do this. In the custom filter you can omit the list property altogether when the whole set of MyChildPojo objects are just shell.

Annotate MyChildPojo class with

@JsonInclude(value = JsonInclude.Include.NON_EMPTY, valueFilter = EmptyListFilter.class)
public class MyChildPojo {
...
}

And define EmptyListFilter something like the following

public class EmptyListFilter {
    @Override
    public boolean equals(Object obj) {
        if (obj == null || !(obj instanceof List)) {return false;}
        Optional<Object> result = ((List)obj).stream().filter(
                eachObj -> Arrays.asList(eachObj.getClass().getDeclaredFields()).stream().filter(eachField -> {
                    try {
                        eachField.setAccessible(true);
                        if ( eachField.get(eachObj)  != null && !eachField.get(eachObj).toString().isEmpty()) {
                            return true;
                        }
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                    return false;
                }).count() > 0).findAny();
       return  !result.isPresent();
    }
}

Example uses the following dependencies on Java:8

   compile group: 'com.fasterxml.jackson.core', name: 'jackson-annotations', version: '2.11.0'
   compile group: 'com.fasterxml.jackson.core', name: 'jackson-databind', version: '2.9.4'

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