ObjectMapper setSerializationInclusion(JsonInclude.Include.NON_NULL) setting is not reflected

Question

ObjectMapper still includes null values. I tried a lot of solutions found here, but nothing works. I cannot use json annotation, so my only solution is predefined setting of mapper, but this was not reflected. I thought this was due to caching of objectMapper. But my only modifies of mapper are made in Constructor. So caching would not be a problem

Dependencies:

Log4J2: 2.17.1
Fasterxml Jackson annotation: 2.13.2
Fasterxml Jackson databind: 2.13.2
Wildfly: 20.0.1
OpenJDK: 11.0.14.1

I have an objectMapper defined as global value which is instantiated in constructor. Then I have one method for building a JSON which accepts key and value. As value can by anything.

private final ObjectMapper jsonMapper;

public SomeConstructor() {
    this.jsonMapper = new ObjectMapper();
    this.jsonMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
    this.jsonMapper.setDefaultPropertyInclusion(JsonInclude.Include.NON_NULL);
}

@Override
public void setJsonVar(String jsonVar, String jsonKey, Object values) {

    // loads ObjectNode from memory if exists
    ObjectNode jsonNode = getJsonVar(jsonVar);

    // lazy init if ObjectNode not exists
    if (jsonNode == null) {
        jsonNode = jsonMapper.createObjectNode();
    }
    // add object
    jsonNode.putPOJO(jsonKey, values);
}

Usage:

setJsonVar("var-A", "key-A", 1);
setJsonVar("var-A", "key-B", null);
print("var-a");

Expectation:

I want to avoid null values in JSON.

Expected: var-A: { "key-A":1 } Got: var-A: { "key-A":1, "key-B":null }

Why does this happen and what can I do to work around this?

Answer 1

This option is applicable when serializing objects, custom objects or a Map for example, but not when working with json tree. Consider this Foo class:

public class Foo {

    private String id;
    private String name;

    //getters and setters
}

The option to exclude nulls will work as expected with it.

Main method to illustrate it:

public class Main {

    public static void main(String[] args) throws Exception {
        serializeNulls();
        System.out.println();
        doNotSerializeNulls();
    }

    private static void serializeNulls() throws Exception {
        ObjectMapper jsonMapper = new ObjectMapper();
        Foo foo = new Foo();
        foo.setId("id");
        System.out.println("Serialize nulls");
        System.out.println(jsonMapper.writeValueAsString(foo));

        Map<String, Object> map = new LinkedHashMap<>();
        map.put("key1", "val1");
        map.put("key2", null);
        System.out.println(jsonMapper.writeValueAsString(map));
    }

    private static void doNotSerializeNulls() throws Exception {
        ObjectMapper jsonMapper = new ObjectMapper();
        jsonMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
        jsonMapper.setDefaultPropertyInclusion(JsonInclude.Include.NON_NULL);

        Foo foo = new Foo();
        foo.setId("id");
        System.out.println("Do not serialize nulls");
        System.out.println(jsonMapper.writeValueAsString(foo));

        Map<String, Object> map = new LinkedHashMap<>();
        map.put("key1", "val1");
        map.put("key2", null);
        System.out.println(jsonMapper.writeValueAsString(map));
    }
}