org.codefx.libfx.serialization

Class SerializableOptional<T extends Serializable>

java.lang.Object

org.codefx.libfx.serialization.SerializableOptional<T>

Type Parameters:

T - the type of the wrapped value

All Implemented Interfaces:

Serializable

public final class SerializableOptional<T extends Serializable>
extends Object
implements Serializable

Convenience class to wrap an Optional for serialization. Instances of this class are immutable.

Note that it does not provide any of the methods Optional has as its only goal is to enable serialization. But it holds a reference to the Optional which was used to create it (can be accessed with asOptional()). This Optional instance is of course reconstructed on deserialization, so it will not be the same as the one specified for its creation.

The class can be used as an argument or return type for serialization-based RPC technologies like RMI.

There are three ways to use this class to serialize instances which have an optional field.

Transform On Serialization

The field can be declared as transient Optional<T> optionalField, which will exclude it from serialization.

The class then needs to implement custom (de)serialization methods writeObject and readObject. They must transform the optionalField to a SerializableOptional when writing the object and after reading such an instance transform it back to an Optional.

Example

 private void writeObject(ObjectOutputStream out) throws IOException {
        out.defaultWriteObject();
        out.writeObject(
                SerializableOptional.fromOptional(optionalField));
 }

 private void readObject(ObjectInputStream in)
        throws IOException, ClassNotFoundException {

        in.defaultReadObject();
        optionalField =
                ((SerializableOptional<T>) in.readObject()).toOptional();
 }
 

Transform On Replace

If the class is serialized using the Serialization Proxy Pattern (see Effective Java, 2nd Edition by Joshua Bloch, Item 78), the proxy can have an instance of SerializableOptional to clearly denote the field as being optional.

In this case, the proxy needs to transform the Optional to SerializableOptional in its constructor (using fromOptional(Optional)) and the other way in readResolve() (with asOptional()).

Transform On Access

The field can be declared as SerializableOptional<T> optionalField. This will include it in the (de)serialization process so it does not need to be customized.

But methods interacting with the field need to get an Optional instead. This can easily be done by writing the accessor methods such that they transform the field on each access.

Note that asOptional() simply returns the Optional which with this instance was created so no constructor needs to be invoked.

Example

Note that it is rarely useful to expose an optional field via accessor methods. Hence the following are private and for use inside the class.

 private Optional<T> getOptionalField() {
        return optionalField.asOptional();
 }

 private void setOptionalField(Optional<T> optionalField) {
        this.optionalField = SerializableOptional.fromOptional(optionalField);
 }
 

See Also:

Serialized Form

Method Summary

Modifier and Type	Method and Description
Optional<T>	asOptional() Returns the Optional instance with which this instance was created.
static <T extends Serializable> SerializableOptional<T>	empty() Creates a serializable optional which wraps an empty optional.
static <T extends Serializable> SerializableOptional<T>	fromOptional(Optional<T> optional) Creates a serializable optional from the specified optional.
static <T extends Serializable> SerializableOptional<T>	of(T value) Creates a serializable optional for the specified value by wrapping it in an Optional.
static <T extends Serializable> SerializableOptional<T>	ofNullable(T value) Creates a serializable optional for the specified value by wrapping it in an Optional.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

fromOptional

public static <T extends Serializable> SerializableOptional<T> fromOptional(Optional<T> optional)

Creates a serializable optional from the specified optional.

Type Parameters:

T - the type of the wrapped value

Parameters:

optional - the Optional from which the serializable wrapper will be created

Returns:

a SerializableOptional which wraps the specified optional

empty

public static <T extends Serializable> SerializableOptional<T> empty()

Creates a serializable optional which wraps an empty optional.

Type Parameters:

T - the type of the non-existent value

Returns:

a SerializableOptional which wraps an empty Optional

See Also:

Optional.of(Object)

of

public static <T extends Serializable> SerializableOptional<T> of(T value)
                                                           throws NullPointerException

Creates a serializable optional for the specified value by wrapping it in an Optional.

Type Parameters:

T - the type of the wrapped value

Parameters:

value - the value which will be contained in the wrapped Optional; must be non-null

Returns:

a SerializableOptional which wraps the an optional for the specified value

Throws:

NullPointerException - if value is null

See Also:

Optional.of(Object)

ofNullable

public static <T extends Serializable> SerializableOptional<T> ofNullable(T value)

Creates a serializable optional for the specified value by wrapping it in an Optional.

Type Parameters:

T - the type of the wrapped value

Parameters:

value - the value which will be contained in the wrapped Optional; may be null

Returns:

a SerializableOptional which wraps the an optional for the specified value

See Also:

Optional.ofNullable(Object)

asOptional

public Optional<T> asOptional()

Returns the Optional instance with which this instance was created.

Returns:

this instance as an Optional