How do I make jackson not serialize primitives with default value

Question

In Jackson, it is possible to use JsonSerialize annotation on a POJO in order to prevent null objects from being serialized (@JsonSerialize(include=JsonSerialize.Inclusion.NON_NULL)). Primitives, however, cannot be set to null, so this annotation doesn't work for something like an int that hasn't been touched and defaults to 0.

Is there an annotation that would allow me to say something like "For this class, don't serialize primitives unless they are different than their default values" or "For this field, don't serialize it if its value is X"?

Answer 1

If you're using a recent version of Jackson you can use JsonInclude.Include.NON_DEFAULT which should work for primitives.

The downside to this approach is that setting a bean property to its default value will have no effect and the property still won't be included:

@JsonInclude(Include.NON_DEFAULT)
public class Bean {
  private int val;
  public int getVal() { return val; }
  public void setVal(int val) { this.val = val; }
}

Bean b = new Bean();
b.setVal(0);
new ObjectMapper().writeValueAsString(b); // "{}" 

Answer 2

The fact is that in Java the class loader will set to the default value all not initialized primitive properties (int = 0, boolean = false etc...), so you can't distinguish them from those set explicitly by your app. In my opinion you have two options:

• Use corresponding wrapper objects instead of primitives (Integer,Boolean,Long..)
• As already suggested, define a custom serializer