Two things I really like about Guava 11's CacheLoader (thanks, Google!) are loadAll(), which allows me to load multiple keys at once, and reload(), which allows me to reload a key asynchronously when it's "stale" but an old value exists. I'm curious as to how they play together, since reload() operates on but a single key.
Concretely, extending the example from CachesExplained:
LoadingCache<Key, Graph> graphs = CacheBuilder.newBuilder()
.maximumSize(1000)
.refreshAfterWrite(1, TimeUnit.MINUTES)
.build(
new CacheLoader<Key, Graph>() {
public Graph load(Key key) { // no checked exception
return getGraphFromDatabase(key);
}
public Map<Key, Graph> loadAll(Iterable<? extends K> keys) {
return getAllGraphsFromDatabase(keys);
}
public ListenableFuture<Graph> reload(final Key key, Graph prevGraph) {
if (neverNeedsRefresh(key)) {
return Futures.immediateFuture(prevGraph);
} else {
// asynchronous!
return ListenableFutureTask.create(new Callable<Graph>() {
public Graph call() {
return getGraphFromDatabase(key);
}
});
}
}
});
...where "getAllGraphsFromDatabase()" does an aggregate database query rather than length(keys) individual queries.
How do these two components of a LoadingCache play together? If some keys in my request to getAll() aren't present in the cache, they are loaded as a group with loadAll(), but if some need refreshing, do they get reloaded individually with load()? If so, are there plans to support a reloadAll()?
