package storm.trident.state.map;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import storm.trident.util.LRUMap;
/**
* Useful to layer over a map that communicates with a database. you generally layer opaque map over this over your database store
* @author nathan
* @param <T>
*/
public class CachedMap<T> implements IBackingMap<T> {
LRUMap<List<Object>, T> _cache;
IBackingMap<T> _delegate;
public CachedMap(IBackingMap<T> delegate, int cacheSize) {
_cache = new LRUMap<List<Object>, T>(cacheSize);
_delegate = delegate;
}
@Override
public List<T> multiGet(List<List<Object>> keys) {
Map<List<Object>, T> results = new HashMap<List<Object>, T>();
List<List<Object>> toGet = new ArrayList<List<Object>>();
for(List<Object> key: keys) {
if(_cache.containsKey(key)) {
results.put(key, _cache.get(key));
} else {
toGet.add(key);
}
}
List<T> fetchedVals = _delegate.multiGet(toGet);
for(int i=0; i<toGet.size(); i++) {
List<Object> key = toGet.get(i);
T val = fetchedVals.get(i);
_cache.put(key, val);
results.put(key, val);
}
List<T> ret = new ArrayList<T>(keys.size());
for(List<Object> key: keys) {
ret.add(results.get(key));
}
return ret;
}
@Override
public void multiPut(List<List<Object>> keys, List<T> values) {
cache(keys, values);
_delegate.multiPut(keys, values);
}
private void cache(List<List<Object>> keys, List<T> values) {
for(int i=0; i<keys.size(); i++) {
_cache.put(keys.get(i), values.get(i));
}
}
}