Question

Using Jersey and Jackson to create a REST interface, how do I get List fields to be serialized as a list when there are 0 or 1 elements in them. For example:

@XmlRootElement(name="foo")
public class Foo {
  @XmlElement
  public List<Bar> getBars() {
    return this.bars;
  }
}

@Path("foo")
public FooResource {
  @GET
  public Foo getFoo() {
    return theFoo;
  }
}

When bars has no elements, the result serializes as null and when it contains a single element, it serializes as that element, not an array containing a single element. Is there a way to get these to always serialize as an array?

For reference, I’m using Jersey 1.10 and Jackson 1.9.2.

Answer 1

I am pretty sure that you are not actually using Jackson (“POJO” variant of JSON serialization), since Jackson would not convert single-element arrays or lists to anything else. So you are probably using one of legacy output methods (like jettison); meaning that if you configure system to use POJO mapping it should just work.