Why jackson is serializing transient member also?

Question

I am serializing a POJO into JSON using Jackson 2.1.4 but I want to ignore a particular field from getting serialized. I used transient but still it is serializing that element.

public class TestElement {

    int x;

    private transient String y;

    public int getX() {
        return x;
    }

    public void setX(int x) {
        this.x = x;
    }

    public String getY() {
        return y;
    }

    public void setY(String y) {
        this.y = y;
    }
}

I am serializing as following:

public static void main(String[] args) throws JsonProcessingException {
    TestElement testElement = new TestElement();
    testElement.setX(10);
    testElement.setY("adasd");
    ObjectMapper om = new ObjectMapper();
    String serialized = om.writeValueAsString(testElement);
    System.err.println(serialized);
}

Please don't suggest @JsonIgnore as I don't want to tie my model to jackson specific annotations. Can it be done using transient only? Is there any API on objectmapper for visibility settings?

Answer 1

The reason Jackson serializes the transient member is because the getters are used to determine what to serialize, not the member itself - and since y has a public getter, that gets serialized. If you want to change that default and have Jackson use fields - simply do:

om.setVisibilityChecker(
  om.getSerializationConfig()
    .getDefaultVisibilityChecker()
    .withFieldVisibility(JsonAutoDetect.Visibility.ANY)
    .withGetterVisibility(JsonAutoDetect.Visibility.NONE)
);

Another way to ignore a property on serialization is to do it directly on the class:

@JsonIgnoreProperties(value = { "y" })
public class TestElement {
...

And another way is directly on the field:

public class TestElement {

    @JsonIgnore
    private String y;
...

Hope this helps.

Answer 2

A new way to stop Jackson from serializing and deserializing is to call mapper.configure(MapperFeature.PROPAGATE_TRANSIENT_MARKER, true).

Answer 3

You can configure it with springs properties

spring.jackson.mapper.propagate-transient-marker=true

Answer 4

I can't make comments so complete the previous response here, changing the (now) deprecated method setVisibilityChecker and adding a missing clause for booleans:

mapper.setVisibility(
    mapper.getSerializationConfig().
    getDefaultVisibilityChecker().
    withFieldVisibility(JsonAutoDetect.Visibility.ANY).
    withGetterVisibility(JsonAutoDetect.Visibility.NONE).
    withIsGetterVisibility(JsonAutoDetect.Visibility.NONE)
);