tools.com.google.gson

Interface JsonSerializer<T>

Type Parameters:

T - type for which the serializer is being registered. It is possible that a serializer may be asked to serialize a specific generic type of the T.

public interface JsonSerializer<T>

Interface representing a custom serializer for Json. You should write a custom serializer, if you are not happy with the default serialization done by Gson. You will also need to register this serializer through com.google.gson.GsonBuilder#registerTypeAdapter(Type, Object).

Let us look at example where defining a serializer will be useful. The Id class defined below has two fields: clazz and value.

 public class Id<T> {
   private final Class<T> clazz;
   private final long value;

   public Id(Class<T> clazz, long value) {
     this.clazz = clazz;
     this.value = value;
   }

   public long getValue() {
     return value;
   }
 }
 

The default serialization of Id(com.foo.MyObject.class, 20L) will be {"clazz":com.foo.MyObject,"value":20}. Suppose, you just want the output to be the value instead, which is 20 in this case. You can achieve that by writing a custom serializer:

 class IdSerializer implements JsonSerializer<Id>() {
   public JsonElement serialize(Id id, Type typeOfId, JsonSerializationContext context) {
     return new JsonPrimitive(id.getValue());
   }
 }
 

You will also need to register IdSerializer with Gson as follows:

 Gson gson = new GsonBuilder().registerTypeAdapter(Id.class, new IdSerializer()).create();
 

New applications should prefer TypeAdapter, whose streaming API is more efficient than this interface's tree API.

Author:

Inderjeet Singh, Joel Leitch

Method Summary

Modifier and Type	Method and Description
JsonElement	serialize(T src, java.lang.reflect.Type typeOfSrc, JsonSerializationContext context) Gson invokes this call-back method during serialization when it encounters a field of the specified type.

Method Detail

serialize

JsonElement serialize(T src,
                      java.lang.reflect.Type typeOfSrc,
                      JsonSerializationContext context)

Gson invokes this call-back method during serialization when it encounters a field of the specified type.

In the implementation of this call-back method, you should consider invoking JsonSerializationContext.serialize(Object, Type) method to create JsonElements for any non-trivial field of the src object. However, you should never invoke it on the src object itself since that will cause an infinite loop (Gson will call your call-back method again).

Parameters:

src - the object that needs to be converted to Json.

typeOfSrc - the actual type (fully genericized version) of the source object.

Returns:

a JsonElement corresponding to the specified object.