Registry optimization with Guice

Question

• Hi! Today I thought about a kind of optimization and have some questions...

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Context : I'm developing in Java using Guice 2.

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In my web application, I have a registry of converter to convert on the fly to a certain type. A converter is described as follows:

public class StringToBoolean implements Converter<String, Boolean>
{

  @Override
  public Boolean convert(String from) 
  {
      return Boolean.valueOf(from);
  }

}

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My registry is none other than a Map:

public class ConverterRegistryImpl implements ConverterRegistry
{  

  private Map<Key,Converter<?,?>> converterRegistry = new HashMap<Key, Converter<?,?>>();

  @Override
  public <F, T> void register(Class<F> fromType, Class<T> toType, Converter<F, T> converter) 
  {
      converterRegistry.put(new Key(fromType,toType), converter);
  }

}

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Finally I register my converter in my registry (class: ServletModule:configureServlets())
I think this step could be optimized...

ConverterRegistryImpl registry = new ConverterRegistryImpl();
registry.register(String.class, Integer.class, new StringToInteger());
registry.register(String.class, Boolean.class, new StringToBoolean());
...
//Then I bind the registry to this current instance...
bind(ConverterRegistry.class).toInstance(registry)

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In this way I can use it everywhere like this :

@Inject 
ConverterRegistry converter;

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• Well I'm searching the best way to implement this using Guice.
• More generally, how did you build that sort of registry with Guice (or without) ?

Thanks in advance !

Answer 1

Don't know what exactly do you mean by "optimize". One of drawbacks of your approach is that you create your converters and registry by hand, so you do not use benefits of dependency injection for them. Also you can not accumulate converters from different modules.

This can be fixed with multibindings extension to guice: http://code.google.com/p/google-guice/wiki/Multibindings

    Injector injector = Guice.createInjector(new Module() {
        @Override
        public void configure(Binder binder) {
            @SuppressWarnings("rawtypes")
            Multibinder<Converter> converterBinder = Multibinder.newSetBinder(binder, Converter.class);
            converterBinder.addBinding().to(StringBooleanConverter.class);
            converterBinder.addBinding().to(BooleanStringConverter.class);
        }
    });
    ConverterRegistryImpl registry = injector.getInstance(ConverterRegistryImpl.class);

The full code is avaliable at: https://gist.github.com/1217563