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ClassAncestry.java
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88 lines (76 loc) · 2.84 KB
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/*
* Copyright (c) 2008-2014 MongoDB, 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.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.ConcurrentMap;
import static java.util.Collections.unmodifiableList;
import static org.bson.util.CopyOnWriteMap.newHashMap;
class ClassAncestry {
/**
* getAncestry
*
* 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.
*
* Does not need to be synchronized, races are harmless as the Class graph
* does not change at runtime.
*/
public static <T> List<Class<?>> getAncestry(Class<T> c) {
final ConcurrentMap<Class<?>, List<Class<?>>> cache = getClassAncestryCache();
while (true) {
List<Class<?>> cachedResult = cache.get(c);
if (cachedResult != null) {
return cachedResult;
}
cache.putIfAbsent(c, computeAncestry(c));
}
}
/**
* computeAncestry, starting with children and going back to parents
*/
private static List<Class<?>> computeAncestry(Class<?> c) {
final List<Class<?>> result = new ArrayList<Class<?>>();
result.add(Object.class);
computeAncestry(c, result);
Collections.reverse(result);
return unmodifiableList(new ArrayList<Class<?>>(result));
}
private static <T> void computeAncestry(Class<T> c, List<Class<?>> result) {
if ((c == null) || (c == Object.class)) {
return;
}
// first interfaces (looks backwards but is not)
Class<?>[] interfaces = c.getInterfaces();
for (int i = interfaces.length - 1; i >= 0; i--) {
computeAncestry(interfaces[i], result);
}
// next superclass
computeAncestry(c.getSuperclass(), result);
if (!result.contains(c))
result.add(c);
}
/**
* classAncestryCache
*/
private static ConcurrentMap<Class<?>, List<Class<?>>> getClassAncestryCache() {
return (_ancestryCache);
}
private static final ConcurrentMap<Class<?>, List<Class<?>>> _ancestryCache = newHashMap();
}