//////////////////////
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * http://www.apache.org/licenses/LICENSE-2.0
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied.
 * See the License for the specific language governing permissions
 * and limitations under the License.
//////////////////////

[[core-api-serialization,Serialization]]
= Serialization =

State can be serialized and deserialized using the Serialization API which is a Service API implemented
by SPI and extensions.

TIP: +Serialization extends Serializer, Deserializer+. See the <<javadocs>> for interfaces detail.

The Serialization mechanism apply to the following object types :

    * ValueComposite,
    * EntityReference & Identity,
    * Array, Iterable & Stream,
    * Map,
    * Plain Values.

Nested Plain Values, EntityReferences, Identities, Arrays, Iterables, Streams, Maps, ValueComposites are supported.
EntityComposites and EntityReferences are serialized as their identity string.

Plain Values can be one of :

    * String,
    * Character or char,
    * Boolean or boolean,
    * Integer or int,
    * Long or long,
    * Short or short,
    * Byte or byte,
    * Float or float,
    * Double or double,
    * BigInteger,
    * BigDecimal,
    * java.time types.

TIP: Serialization behaviour can be tuned with options.
Every +Serializer+ methods can take a +Serializer.Options+ object that contains flags to change how some
values are serialized. See the <<javadocs>> for more details.

Values of unknown types and all arrays are considered as +java.io.Serializable+ and by so are (de)serialized to (from)
base64 encoded bytes using pure Java serialization. If it happens that the value is not Serializable or the input to
deserialize is invalid, a +SerializationException+ is thrown.

Methods of +Serializer+ allow to specify if the serialized state should contain extra type information about the
serialized value. Having type information in the serialized payload allows to keep actual ValueComposite types and by so
circumvent +AmbiguousTypeException+ when deserializing.

Core Runtime provides a default Serialization system based on `javax.json` types.

Let's see how it works in practice.

[snippet,java]
----
source=core/api/src/test/java/org/apache/polygene/api/value/DocumentationSupport.java
tag=default
----

Reading this first example step by step we ;

    . declare a ValueComposite,
    . assemble it,
    . assemble default services including default `Serialization`,
    . create a new Value instance,
    . use the +ValueComposite#toString()+ method to get a JSON representation of the Value,
    . and finally, use the +Module#newValueFromSerializedState()+ method to create a new Value instance from the JSON
      state.

+ValueComposite#toString()+ method leverage Value Serialization and by so provide JSON based representation. The Module
API allows to create new Value instances from serialized state.

On top of that, Application assemblies can register different implementation of Serialization as Services to
support more formats, see the <<extensions>> section. Note that the default behaviour described above is overriden if a
Serialization Service is visible.

Let's see how to use the Serialization Services.

[snippet,java]
----
source=core/api/src/test/java/org/apache/polygene/api/value/DocumentationSupport.java
tag=service
----

In this second example, we ;

    . declare a ValueComposite,
    . assemble it,
    . assemble a Serialization Service backed by the +javax.json+ types,
    . get the +Serializer+ and +Deserializer+ Services injected,
    . create a new Value instance,
    . use the +Serializer#serialize()+ method to get a JSON representation of the Value,
    . and finally, use the +Deserializer#deserialize()+ method to create a new Value instance from the JSON state.