Java Gson deserialization. How to handle interfaces?

Question

Java

I have these types:

interface IBla
{
  
}

class Bla implement IBla
{
  private int field;
}

class Bla2 implement IBla
{
  private int field;
  private int field2;
}

class Foo
{
  IBla kuku;
}

Serialization of objects of the Foo class proceeds normally.
But here's how to deserialize the received json back? The problem is that you need to somehow explain to gson what type of object to take (Bla or Bla2) in order to properly deserialize. How can I do that?

Answer 1

there is a wild idea to make Foo typed, I don’t know how correct it will be .. like this

class Foo<T extends IBla>
{
  T kuku;
}

and deserialize like

Foo foo = gson.fromJson(jsonString, new TypeToken<Foo<Bla2>>() {}.getType())

Answer 2

Depends on the implementation you are using. In Jackson it's done like this:

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "type")
@JsonSubTypes({
        @JsonSubTypes.Type(value = Bla.class, name = "Bla"),
        @JsonSubTypes.Type(value = Bla2.class, name = "Bla2")
})
interface IBla {}

With the @JsonSubTypes annotation, you specify a list of all possible interface implementations.
The JsonTypeInfo specifies that the incoming JSON will have a "type" field that will tell you what type to cast the abstract IBla to when the JSON message is received.

Answer 3

You write your own deserializer/type adapter/instance creator.
https://sites.google.com/site/gson/gson-user-guide...
Then you register all this when you create a Gson object via GsonBuilder