How to handle checked exceptions inside a functor object in Java

We use the http://jedi.codehaus.org libraries for working with collections and manipulating them in a functional way. We recently came across a problem when do开发者_如何学Pythoning something similar to the following:

public class Address {
    //constructors and stuff

    public KiloWatts electricityConsumed(Duration timePeriod) throw NoElectricitySupply {
        .... does stuff but can throw checked exception
    } 
}

given we have a collection of addresses and we wanted to perform something on the UnitsOfElectricity associated with each address, how would you handle the thrown exception e.g.:

public KiloWatts totalEnergyConsumed(Address... addresses, final Duration timePeriod) {
     List<KiloWatts> energyConsumedPerAddress = FunctionalPrimitives.collect(addresses, new Functor<Address, KiloWatts>{
         public KiloWatts execute(Address address){
              try {
                  return address.energyConsumed(timePeriod);
              } catch (NoElectricitySupply e) {

                  //What do you do here?

              }
         }
     });
}

How would you handle the exception?

As far as I can tell, you have 2 options:

1. throw a runtime exception (and ignore it); or
2. throw a runtime exception, using it to 'marshall' the checked exception past the interface boundary.

for (2), something like:

public KiloWatts totalEnergyConsumed(Address... addresses, final Duration timePeriod) {
    try {
        List<KiloWatts> energyConsumedPerAddress = FunctionalPrimitives.collect(addresses, new Functor<Address, KiloWatts>{
            public KiloWatts execute(Address address){
                try {
                    return address.energyConsumed(timePeriod);
                } catch (NoElectricitySupply e) {
                    throw new RuntimeException("internal marshalling exception", e);
                }
           }
       });
    } catch(RuntimeException re) {
        throw e.getCause();
    }
}

why not return an Option<Kilowatts> from the functor so you can return None for the exceptional case? You can then flatten the List<Option<Kilowatts>> to List<Kilowatts> (there is a method on FunctionalPrimitives for that).

Alternatively, if you have control over the energyConsumed method which throws the Exception, replace the thrown Exception with are return type of Either<String, Kilowatts> (the String can contain an error message or something - I would need to see more to understand what to do there).

Using Either instead of exceptions enables composition, exceptions break composition completely.

If NoElectricitySupply is logically equivalent to zero KiloWatts, shouldn't you just return such object?

If they're not quite equivalent, you could create some sort of special NoKiloWatts subclass and return an instance of such in the catch block.