Tip: Builder Pattern

[Niclas Hedhman <ni...@hedhman.org>]

I have for quite long been a little bit irritated over the Builders that
are required, especially since often I forget what is required and get a
runtime exception very late. Also, I tend to duplicate the builder
boilerplate all over the place.

Recently, I have tried to remember to do the following pattern...

Say we have a Value like;

public interface Address
{
    Property<String> street();

    Association<City> city();

    Property<String> zipCode();

    Association<Country> country();

}

And say for the sake of argument that the Country is an Entity, but City is
a Value.

I would then consider to create a explicit builder, inside the same
interface declaration;

class Builder
{

    private final UnitOfWorkFactory uowf;
    private final ValueBuilder<Address> addressBuilder;
    private final ValueBuilder<City> cityBuilder;
    private final Address addressPrototype;
    private final City cityPrototype;

    public Builder( @Structure ValueBuilderFactory vbf, @Structure
UnitOfWorkFactory uowf )
    {
        this.uowf = uowf;
        addressBuilder = vbf.newValueBuilder( Address.class );
        cityBuilder = vbf.newValueBuilder( City.class );
        addressPrototype = addressBuilder.prototype();
        cityPrototype = cityBuilder.prototype();
    }

    @UnitOfWorkPropagation( MANDATORY)
    public Address create( String street, String cityName, String
zipCode, String countryCode )    {

cityPrototype.name().set( cityName );
City city = cityBuilder.newInstance();
Country country = uowf.currentUnitOfWork().get( Country.class,
StringIdentity.fromString( countryCode ) );
addressPrototype.street().set( street );
addressPrototype.city().set( city );
addressPrototype.zipCode().set( zipCode );
addressPrototype.country().set( country );
return addressBuilder.newInstance();
}
}

And this is an Object

so,elsewhere

    @Structure
    private ObjectFactory factory;


        factory.newObject( Address.Builder.class ).create( "10, CH5A,
Canary Residence", "Cheras", "43200", "MY" );


And if I am really pressed for performance, then Address.Builder instance
can also be kept as a field, and a bunch of value builder initialization is
not happening on each instantiation.


Cheers
-- 
Niclas Hedhman, Software Developer
http://polygene.apache.org - New Energy for Java