import com.esotericsoftware.kryo.serializers.CollectionSerializer;
import com.esotericsoftware.kryo.serializers.MapSerializer;

/**
 * A serializer class for handling object serialization and deserialization.
 * <p>
 * This class provides serialization capabilities using different serializers,
 * currently supporting Kryo and JavaBin serialization formats. The serializer

        String original = "Hello, World!";

        byte[] serialized = serializer.fromObjectToBinary(original);
        assertNotNull(serialized, "Serialized data should not be null");
        assertTrue("Serialized data should not be empty", serialized.length > 0);

        Object deserialized = serializer.fromBinaryToObject(serialized);
        assertNotNull(deserialized, "Deserialized object should not be null");

* Existing usages of Serializer outside of this infrastructure should be migrated to use it.
* Existing usages of Java serialization should be migrated to use it.
* It is ok for Serializer to be used as a replacement for Java serialization as a migration step.

/// tip

You will normally have much better performance using a [Response Model](../tutorial/response-model.md) than returning a `JSONResponse` directly, as that way it serializes the data using Pydantic, in Rust.

///

## Return a `Response` { #return-a-response }

You can return a `Response` or any sub-class of it.

/// info

`JSONResponse` itself is a sub-class of `Response`.

///

        return ObjectInputFilter.Status.REJECTED;
    };

    /**
     * Tests if the object can be serialized.
     *
     * @param obj the object to be serialized (must not be {@literal null})
     * @return the deserialized object
     */
    public static Object serialize(final Object obj) {
        assertArgumentNotNull("obj", obj);

        final byte[] binary = fromObjectToBinary(obj);

    category=FastAPIDeprecationWarning,
    stacklevel=2,
)
class UJSONResponse(JSONResponse):
    """JSON response using the ujson library to serialize data to JSON.

    **Deprecated**: `UJSONResponse` is deprecated. FastAPI now serializes data
    directly to JSON bytes via Pydantic when a return type or response model is
    set, which is faster and doesn't need a custom response class.

    Read more in the

            raise ResponseValidationError(
                errors=errors,
                body=response_content,
                endpoint_ctx=ctx,
            )
        serializer = field.serialize_json if dump_json else field.serialize
        return serializer(
            value,
            include=include,
            exclude=exclude,
            by_alias=by_alias,
            exclude_unset=exclude_unset,

   * concurrent maps whose content may change while the method is running.
   *
   * <p>The serialized output consists of the number of entries, first key, first value, second key,
   * second value, and so on.
   */
  static <K extends @Nullable Object, V extends @Nullable Object> void writeMap(
      Map<K, V> map, ObjectOutputStream stream) throws IOException {
    stream.writeInt(map.size());

   * concurrent maps whose content may change while the method is running.
   *
   * <p>The serialized output consists of the number of entries, first key, first value, second key,
   * second value, and so on.
   */
  static <K extends @Nullable Object, V extends @Nullable Object> void writeMap(
      Map<K, V> map, ObjectOutputStream stream) throws IOException {
    stream.writeInt(map.size());

If you declare the return type as `AsyncIterable[Item]`, FastAPI will use it to **validate**, **document**, and **serialize** the data using Pydantic.

{* ../../docs_src/server_sent_events/tutorial001_py310.py ln[1:25] hl[10:12,23] *}

/// tip

As Pydantic will serialize it in the **Rust** side, you will get much higher **performance** than if you don't declare a return type.

///