How to Produce prototype objects from singleton? (Design help needed)

Question

I'm relatively new to Spring and I've got myself dug in a hole. I'm trying to model motor cars. Each model has it's own builder object, and I have a BuilderFactory that returns the correct builder based upon user selection from a web-app.

So I'm looking for suggestions on how to approach this problem where I need to create a number of individual vehicles, but I don't know what type of vehicle I'm going to need until run-time, and each vehicle needs to be unique to the user.

What I've got at the moment is shown below. The problem I have at the moment is that because the individual builders are singletons so are the individual vehicles. I need them to be prototypes. I know it all looks pretty horrible so I'm sure there must be a better way of doing this.

The top level from the web-app looks like;

Vehicle vehicle = vehicleBuilderFactory.getBuilder(platform).build();

My vehicleBuilderFactory looks like this;

@Service
public class VehicleBuilderFactory {

@Autowired
Discovery3Builder discovery3Builder;
@Autowired
Discovery4Builder discovery4Builder;

    // Lots of @Autowired statements here. 

@Autowired
FreeLander2010Builder freeLander2010Builder;



public VehicleBuilder getBuilder(Platform platform) {

    switch (platform.getId()) {

    case 1: return discovery3Builder;
    case 2: return discovery4Builder;

            // Lots of case statements here

            case 44: return freeLander2010Builder;
    default: return null;
    }
}

}

which itself looks pretty horrible. Each individual builder looks like;

@Service
public class DefenderBuilder implements VehicleBuilder {

@Autowired
Defender defender;

// Loads of Defender specific setters ommitted  
@Override
public Vehicle build() {
    return defender;
}

}

and finally the individual vehicle

@Service
@Scope("prototype")
public class Defender extends Vehicle {

}

The main problem now, is that because the builders are singletons, so are the vehicles, and I need them to be prototypes, because User A's Defender is different to user B's Defender.

Answer 1

You can use Spring's ObjectFactory to have it service up prototype scoped beans from a singleton scoped bean. The usage is pretty straightforward:

@Component
class DefenderBuilder implement VechicleBuilder {

  @Autowired
  ObjectFactory<Defender> defenderFactory;

  Defender build() {
     return defenderFactory.getObject()
  }
}

@Component
@Scope("prototype")
class Defender {

}

This returns a new Defender on each call to defenderFactory.getObject()