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[[core-spi-valueserialization,ValueSerialization SPI]]
= ValueSerialization SPI =

== Overview ==

The Zest™ Core Runtime use ValueSerialization to provide string representation of ValueComposites via their `toString()`
method, and, their instanciation from the very same representation via the `newValueFromSerializedState(..)` method of
the ValueBuilderFactory API.

If no ValueSerialization service is visible, a default implementation supporting the JSON format used but note that it
won't be available as a Service. So, in order to use the full ValueSerialization API a ValueSerialization service must
be explicitely assembled in the Application. See the <<extensions>> documentation for details.

== Implementation notes ==

Simply implement ValueSerialization to create an extension for the ValueSerialization SPI.
The Core SPI module provides adapters to create pull-parsing capable ValueSerializers and pull-parsing and tree-parsing
capable ValueDeserializers.

The behaviour described here apply to all ValueSerialization services implemented using the Core SPI adapters. Note that
nothing stops you from implementing an extension for the ValueSerialization SPI without relying on theses adapters.

Theses adapters are tailored for serialization mechanisms that support the following two structures that can be nested:

    * a collection of name/value pairs. In various languages, this is realized as an object, record, struct,
      dictionary, hash table, keyed list, or associative array,
    * an ordered list of values. In most languages, this is realized as an array, vector, list, or sequence ;

in other words, a JSON-like structure.

Special attention is taken when dealing with Maps. They are serialized as an ordered list of collections of
name/value pairs to keep the Map order for least surprise. That way, even when the underlying serialization mechanism
do not keep the collection of name/value pairs order we can rely on it being kept.

Here is a sample Map with two entries in JSON notation to make things clear:

[source,javascript]
----
[
    { "key": "foo",       "value": "bar"   },
    { "key": "cathedral", "value": "bazar" }
]
----

Among Plain Values (see the <<core-api-value,ValueSerialization API>> section) some are considered primitives to
underlying serialization mechanisms and by so handed/come without conversion to/from implementations.

Primitive values can be one of:

    * String,
    * Boolean or boolean,
    * Integer or int,
    * Long or long,
    * Short or short,
    * Byte or byte,
    * Float or float,
    * Double or double.

Serialization is always done in a streaming manner using a pull-parsing based approach.

Deserialization is done in a streaming manner using a pull-parsing based approach except when encountering a
ValueComposite. ValueComposite types are deserialized using a tree-parsing based approach.

All this means that you can serialize and deserialize large collections of values without filling the heap.