/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.apache.hadoop.hbase.util;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.ConcurrentMap;
import java.util.function.Supplier;
import org.apache.hadoop.hbase.classification.InterfaceAudience;
/**
* Utility methods for dealing with Collections, including treating null collections as empty.
*/
@InterfaceAudience.Private
public class CollectionUtils {
private static final List<Object> EMPTY_LIST = Collections.unmodifiableList(new ArrayList<>(0));
@SuppressWarnings("unchecked")
public static <T> Collection<T> nullSafe(Collection<T> in) {
if (in == null) {
return (Collection<T>)EMPTY_LIST;
}
return in;
}
/************************ size ************************************/
public static <T> int nullSafeSize(Collection<T> collection) {
if (collection == null) {
return 0;
}
return collection.size();
}
public static <A, B> boolean nullSafeSameSize(Collection<A> a, Collection<B> b) {
return nullSafeSize(a) == nullSafeSize(b);
}
/*************************** empty ****************************************/
public static <T> boolean isEmpty(Collection<T> collection) {
return collection == null || collection.isEmpty();
}
public static <T> boolean notEmpty(Collection<T> collection) {
return !isEmpty(collection);
}
/************************ first/last **************************/
public static <T> T getFirst(Collection<T> collection) {
if (CollectionUtils.isEmpty(collection)) {
return null;
}
for (T t : collection) {
return t;
}
return null;
}
/**
* @param list any list
* @return -1 if list is empty, otherwise the max index
*/
public static int getLastIndex(List<?> list){
if(isEmpty(list)){
return -1;
}
return list.size() - 1;
}
/**
* @param list
* @param index the index in question
* @return true if it is the last index or if list is empty and -1 is passed for the index param
*/
public static boolean isLastIndex(List<?> list, int index){
return index == getLastIndex(list);
}
public static <T> T getLast(List<T> list) {
if (isEmpty(list)) {
return null;
}
return list.get(list.size() - 1);
}
/**
* In HBASE-16648 we found that ConcurrentHashMap.get is much faster than computeIfAbsent if the
* value already exists. Notice that the implementation does not guarantee that the supplier will
* only be executed once.
*/
public static <K, V> V computeIfAbsent(ConcurrentMap<K, V> map, K key, Supplier<V> supplier) {
return computeIfAbsent(map, key, supplier, () -> {
});
}
/**
* A supplier that throws IOException when get.
*/
@FunctionalInterface
public interface IOExceptionSupplier<V> {
V get() throws IOException;
}
/**
* In HBASE-16648 we found that ConcurrentHashMap.get is much faster than computeIfAbsent if the
* value already exists. So here we copy the implementation of
* {@link ConcurrentMap#computeIfAbsent(Object, java.util.function.Function)}. It uses get and
* putIfAbsent to implement computeIfAbsent. And notice that the implementation does not guarantee
* that the supplier will only be executed once.
*/
public static <K, V> V computeIfAbsentEx(ConcurrentMap<K, V> map, K key,
IOExceptionSupplier<V> supplier) throws IOException {
V v, newValue;
return ((v = map.get(key)) == null && (newValue = supplier.get()) != null
&& (v = map.putIfAbsent(key, newValue)) == null) ? newValue : v;
}
public static <K, V> V computeIfAbsent(ConcurrentMap<K, V> map, K key, Supplier<V> supplier,
Runnable actionIfAbsent) {
V v = map.get(key);
if (v != null) {
return v;
}
V newValue = supplier.get();
v = map.putIfAbsent(key, newValue);
if (v != null) {
return v;
}
actionIfAbsent.run();
return newValue;
}
}