Serialize java object with GSON

Question

I would like to serialize this object to JSON String

public class Person {    public String id;    public String name;    public Person parent; } 

and obtain a result like this:

{id: 1, name: "Joe", parent: 2} 

I tried to use

Person p = new Person(1, "Joe", new Person(2, "Mike")); Gson gson = new GsonBuilder()             .registerTypeAdapter(Persona.class, new PersonSerializer()).create(); String str = gson.toJson(p); 

but instead of that, I got:

"1" 

PersonSerializer:

public class PersonSerializer implements JsonSerializer<Person> {     public JsonElement serialize(Person src, Type typeOfSrc, ...) {         return new JsonPrimitive(src.id);     } } 

Please any suggestion is welcome

Thanks, Mario

Answer 1

In order to get the result you desire, you need to write the serializer like this:

public static class PersonSerializer implements JsonSerializer<Person> {     public JsonElement serialize(final Person person, final Type type, final JsonSerializationContext context) {         JsonObject result = new JsonObject();         result.add("id", new JsonPrimitive(person.getId()));         result.add("name", new JsonPrimitive(person.getName()));         Person parent = person.getParent();         if (parent != null) {             result.add("parent", new JsonPrimitive(parent.getId()));         }         return result;     } } 

The result for

    Person p = new Person(1, "Joe", new Person(2, "Mike"));     com.google.gson.Gson gson = new GsonBuilder().registerTypeAdapter(Person.class, new PersonSerializer())             .create();     System.out.println(gson.toJson(p)); 

will be

{"id":1,"name":"Joe","parent":2} 

Complete code:

import java.lang.reflect.Type;  import com.google.gson.GsonBuilder; import com.google.gson.JsonElement; import com.google.gson.JsonObject; import com.google.gson.JsonPrimitive; import com.google.gson.JsonSerializationContext; import com.google.gson.JsonSerializer;  public class GsonSimpleTest {      public static class Person {         public int id;         public String name;         public Person parent;          public Person(final int id, final String name) {             super();             this.id = id;             this.name = name;         }          public Person(final int id, final String name, final Person parent) {             super();             this.id = id;             this.name = name;             this.parent = parent;         }          public int getId() {             return id;         }          public void setId(final int id) {             this.id = id;         }          public String getName() {             return name;         }          public void setName(final String name) {             this.name = name;         }          public Person getParent() {             return parent;         }          public void setParent(final Person parent) {             this.parent = parent;         }      }      public static class PersonSerializer implements JsonSerializer<Person> {         public JsonElement serialize(final Person person, final Type type, final JsonSerializationContext context) {             JsonObject result = new JsonObject();             result.add("id", new JsonPrimitive(person.getId()));             result.add("name", new JsonPrimitive(person.getName()));             Person parent = person.getParent();             if (parent != null) {                 result.add("parent", new JsonPrimitive(parent.getId()));             }             return result;         }     }      public static void main(final String[] args) {         Person p = new Person(1, "Joe", new Person(2, "Mike"));         com.google.gson.Gson gson = new GsonBuilder().registerTypeAdapter(Person.class, new PersonSerializer())                 .create();         System.out.println(gson.toJson(p));     }  }