A simple Google Guava CacheLoader implementation that submits Function execution to an ExecutorService thus making a LoadingCache asynchronous. Note that threads won't be wasted waiting (at least as long as one doesn't wait on a Future's get() method).

AsyncCacheLoader.java

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;

import com.google.common.base.Function;
import com.google.common.cache.CacheLoader;

public class AsyncCacheLoader<K, V> extends CacheLoader<K, Future<V>> {

	private final ExecutorService _executor;
	private final Function<K, V> _function;

	public AsyncCacheLoader(ExecutorService executor, Function<K, V> function) {
		_executor = executor;
		_function = function;
	}

	public Future<V> load(final K key) throws Exception {
		return _executor.submit(new Callable<V>() {
			public V call() throws Exception {
				return _function.apply(key);
			}
		});
	}
}