Moshiを使ってPOJOからJsonObjectとJsonArrayを作成する ref: http://qiita.com/shts/items/83d261c7666ab0069326

file0.java

public class User {
  @Json(name = "name")
  String name;
  @Json(name = "age")
  int age;

  public User(String name, int age) {
    this.name = name;
    this.age = age;
  }  
}

file1.java

import com.squareup.moshi.Moshi;
import com.squareup.moshi.Types;

String json = new Moshi.Builder().build().adapter(User.class).toJson(new User("hoge", 10));

file2.txt

{"age":10,"name":"hoge"}

file3.java

import com.squareup.moshi.Moshi;
import com.squareup.moshi.Types;
import java.lang.reflect.Type;


List<User> users = new ArrayList<User>();
users.add(new User("hoge", 10));

Type listOfUsersType = Types.newParameterizedType(List.class, User.class);

String json = new Moshi.Builder().build().adapter(listOfUsersType).toJson(users);

file4.txt

[{"age":10,"name":"hoge"}]

file5.java

new Moshi.Builder().build().adapter(Types.newParameterizedType(List.class, User.class)).toJson(Observable.just(new User("hoge", 10)).toList().toBlocking().single());