GSON toJson() method returns null for a POJO

Question

This is my POJO class

public class ResourceRecord {

    public ResourceRecord() {}

    public String name;
    public Integer ttl;
    public String type;
    public String rr;

    @SerializedName("class")
    public String dnsClass;

}

And this the serialisation:

ResourceRecord rr = new ResourceRecord() {
    {
        name = "8.8.8.8";
        dnsClass = "IN";
        ttl = 600;
        rr = "0431shangmao.com.";
        type = "A";
    }
};

String rrStr = new Gson().toJson(rr);

Apparently, rrStr gets null . Why?

I tried annotating the fields with @Expose but the result stayed the same.

UPDATE: I changed to constructing to:

ResourceRecord rr = new ResourceRecord("8.8.8.8", 900,"A","1.dnstest.netshade.net.", "IN");

and it worked.

Answer 1

The reason why it didn't work is because you were creating anonymous innerclass of ResourceRecord when you instantiate using curly braces:

ResourceRecord rr = new ResourceRecord() {
      {
          name = "8.8.8.8";
          dnsClass = "IN";
          ttl = 600;
          rr = "0431shangmao.com.";
          type = "A";
      }
  };

And Gson doesn't support serializing anonymous subclasses.

Answer 2

Try this,

Gson gson = new GsonBuilder().create(); String json = gson.toJson(obj);

obj is the object of pojo class