// ClassMap.java
/**
* Copyright (C) 2008 10gen Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.bson.util;
import java.util.List;
import java.util.Map;
/**
* Maps Class objects to values. A ClassMap is different from a regular Map in
* that get(c) does not only look to see if 'c' is a key in the Map, but also
* walks the up superclass and interface graph of 'c' to find matches. Derived
* matches of this sort are then "cached" in the registry so that matches are
* faster on future gets.
*
* This is a very useful class for Class based registries.
*
* Example:
*
* ClassMap<String> m = new ClassMap<String>(); m.put(Animal.class, "Animal");
* m.put(Fox.class, "Fox"); m.Fox.class) --> "Fox" m.get(Dog.class) --> "Animal"
*
* (assuming Dog.class < Animal.class)
*/
public class ClassMap<T> {
/**
* Walks superclass and interface graph, superclasses first, then
* interfaces, to compute an ancestry list. Supertypes are visited left to
* right. Duplicates are removed such that no Class will appear in the list
* before one of its subtypes.
*/
public static <T> List<Class<?>> getAncestry(Class<T> c) {
return ClassAncestry.getAncestry(c);
}
private final class ComputeFunction implements Function<Class<?>, T> {
@Override
public T apply(Class<?> a) {
for (Class<?> cls : getAncestry(a)) {
T result = map.get(cls);
if (result != null) {
return result;
}
}
return null;
}
};
private final Map<Class<?>, T> map = CopyOnWriteMap.newHashMap();
private final Map<Class<?>, T> cache = ComputingMap.create(new ComputeFunction());
public T get(Object key) {
return cache.get(key);
}
public T put(Class<?> key, T value) {
try {
return map.put(key, value);
} finally {
cache.clear();
}
}
public T remove(Object key) {
try {
return map.remove(key);
} finally {
cache.clear();
}
}
public void clear() {
map.clear();
cache.clear();
}
public int size() {
return map.size();
}
public boolean isEmpty() {
return map.isEmpty();
}
}