Configure Jackson to throw an exception when a field is missing

Question

I have a class like this:

public class Person {
  private String name;
  public String getName(){
    return name;
  }
}

I am using an ObjectMapper configured like this:

ObjectMapper mapper = new ObjectMapper();
mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

I have a String str that contains this { "address" : "something" }. Note that there is no "name" field in the json. If I do something like this:

mapper.readValue(str, Person.class);

then I actually get back a Person object with name set to null. Is there a way to configure the mapper to throw an exception instead, or return a null reference instead of a Person? I want Jackson to consider missing fields a failure and don't want to do explicit null checks on the resulting object's fields.

Adding lombok.NonNull annotation on the field works for me. – user10486998 Oct 11 '18 at 00:57 — user10486998, Oct 11 '18 at 00:57

zopieux · Answer 1 · 2016-01-21T12:42:35.577

41

As of Jackson 2.6, there is a way, but it does not work on class attribute annotations, only constructor annotations:

/* DOES *NOT* THROW IF bar MISSING */
public class Foo {    
    @JsonProperty(value = "bar", required = true)
    public int bar;
}

/* DOES THROW IF bar MISSING */
public class Foo {
    public int bar;
    @JsonCreator
    public Foo(@JsonProperty(value = "bar", required = true) int bar) {
        this.bar = bar;
    }
}

edited Jan 21 '16 at 12:42

answered Jan 21 '16 at 10:47

zopieux

2,854
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2

Will it throw an exception if it's not required and missing? – aclowkay Oct 30 '16 at 10:07
5

It appears that `@JsonCreator` is not required to precede the constructor. (?) – Shawn Dec 01 '17 at 20:58
@aclowkay, Nope, it sets it as null in that case – Dravidian May 14 '21 at 12:09

vtor · Accepted Answer · 2015-02-11T19:00:19.270

6

Unfortunately this is not supported by Jackson at this moment.

Solution could be to add validation in your constructor. As ideally if you don't want to have those values serialized as null's , it does mean you shouldn't have them as null's at all (constructed in other way). For example,

public class Person {
  private String name;
  public Person() {
     checkNotNull(name);
  }
}

however this might not fittable in all situations, specially if you are using your object's other than through serializing/deserializing.

Though they have required attribute in @JsonProperty annotation, it is not supported during deserialization at all, and has been introduced only for decorating JSON schemas. See this topic

edited Feb 11 '15 at 19:00

answered Feb 11 '15 at 09:13

vtor

8,989
7
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This didn't work. I am trying to make it fail on missing properties instead of setting them to null. I don't want it to fail on unknown properties. – mushroom Feb 11 '15 at 18:10
It will not work if you are using primitives like double, int, boolean – Piotr Borowczynski Sep 03 '20 at 07:33

score 0 · Answer 3 · answered Aug 15 '19 at 11:59

I had a similar problem, after deserialization I wanted to know if everything is fine. This method iterates over all fields with a JsonProperty Annotation, checks if it is not null and look deeper if this class in the recursive list (to avoid infinite loops).

private void checkIfFieldsAreNotNull(Object o, List<Class> recursive) {
    Arrays.asList(o.getClass().getDeclaredFields()).stream().filter(field -> field.isAnnotationPresent(JsonProperty.class)).forEach(field -> {
        field.setAccessible(true);
        try {
            assertNotNull(field.get(o));
            if(recursive.contains(field.getType())) {
                checkIfFieldsAreNotNull(field.get(o), recursive);
            }
        } catch (IllegalAccessException e) {
            throw new RuntimeException(e);
        }
    });
}

Configure Jackson to throw an exception when a field is missing

3 Answers3

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