Thursday, April 7, 2016

Converting string configuration properties to other types, with a bit of Optional.

Somedays you come across some code and think that's pretty, why didn't I think of that? So my long time colleague Mark Warner has a nice twist on the standard name/value store pattern using method references to deal with converting from a String.

int size = store.getProperty("cache.limit", 500, Integer::parseInt);
    boolean enabled = store.getProperty("cache.enabled", true, Boolean::getBoolean);

I took his example and refactored it slightly to return Optional, and I ended up with the following:

public Optional<String> getProperty(
        String propertyName) {
    return Optional.ofNullable(map.get(propertyName));
public <T> Optional<T> getProperty(
        String propertyName, 
        ThrowingFunction<String,? extends T,? extends Exception> func ) {

    return getProperty(propertyName).map(val -> {
        try {
            return func.apply( val );
        } catch ( Exception e ) {
            LOGGER.severe( () -> "Invalid property transform, will default " + e.getMessage() );
            return null;

This means that the default value ends up being provided by the Optional which is a nice application of OAOO.

int size = store.getProperty("cache.limit", Integer::parseInt).orElse(500);
    boolean enabled = store.getProperty("cache.enabled", Boolean::getBoolean).orElse(true);

I think this is even tidier; but it does depend on who you feel about using Optionals.