/*
* 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.geode.internal.util;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Properties;
import java.util.Set;
import org.apache.geode.internal.lang.Filter;
/**
* The CollectionUtils class is a utility class for working with the Java Collections framework of
* classes, data structures and algorithms.
* <p/>
*
* @see org.apache.geode.internal.lang.Filter
* @see java.util.Arrays
* @see java.util.Collection
* @see java.util.Collections
* @see java.util.Iterator
* @see java.util.List
* @see java.util.Map
* @see java.util.Set
* @since GemFire 7.0
*/
public abstract class CollectionUtils {
/**
* Returns the specified array as a List of elements.
* <p/>
*
* @param <T> the class type of the elements in the array.
* @param array the object array of elements to convert to a List.
* @return a List of elements contained in the specified array.
* @see java.util.Arrays#asList(Object[])
*/
@SafeVarargs
public static <T> List<T> asList(final T... array) {
List<T> arrayList = new ArrayList<T>(array.length);
Collections.addAll(arrayList, array);
return arrayList;
}
/**
* Returns the specified array as a Set of elements.
* <p/>
*
* @param <T> the class type of the elements in the array.
* @param array the object array of elements to convert to a Set.
* @return a Set of elements contained in the specified array.
* @see java.util.Arrays#asList(Object[])
*/
@SafeVarargs
public static <T> Set<T> asSet(final T... array) {
Set<T> arraySet = new HashSet<T>(array.length);
Collections.addAll(arraySet, array);
return arraySet;
}
/**
* Creates an Properties object initialized with the value from the given Map.
* <p>
*
* @param map the Map supply the keys and value for the Properties object.
* @return a Properties object initialized with the key and value from the Map.
* @see java.util.Map
* @see java.util.Properties
*/
public static Properties createProperties(final Map<String, String> map) {
Properties properties = new Properties();
if (!(map == null || map.isEmpty())) {
for (Entry<String, String> entry : map.entrySet()) {
properties.setProperty(entry.getKey(), entry.getValue());
}
}
return properties;
}
/**
* Null-safe implementation for method invocations that return a List Collection. If the returned
* List is null, then this method will return an empty List in it's place.
* <p/>
*
* @param <T> the class type of the List's elements.
* @param list the target List to verify as not null.
* @return the specified List if not null otherwise return an empty List.
*/
public static <T> List<T> emptyList(final List<T> list) {
return (list != null ? list : Collections.<T>emptyList());
}
/**
* Null-safe implementation for method invocations that return a Set Collection. If the returned
* Set is null, then this method will return an empty Set in it's place.
* <p/>
*
* @param <T> the class type of the Set's elements.
* @param set the target Set to verify as not null.
* @return the specified Set if not null otherwise return an empty Set.
*/
public static <T> Set<T> emptySet(final Set<T> set) {
return (set != null ? set : Collections.<T>emptySet());
}
/**
* Iterates the Collection and finds all object elements that match the Filter criteria.
* <p/>
*
* @param <T> the class type of the Collection elements.
* @param collection the Collection of elements to iterate and filter.
* @param filter the Filter applied to the Collection of elements in search of all matching
* elements.
* @return a List of elements from the Collection matching the criteria of the Filter in the order
* in which they were found. If no elements match the Filter criteria, then an empty List
* is returned.
*/
public static <T> List<T> findAll(final Collection<T> collection, final Filter<T> filter) {
final List<T> matches = new ArrayList<T>(collection.size());
for (final T element : collection) {
if (filter.accept(element)) {
matches.add(element);
}
}
return matches;
}
/**
* Iterates the Collection and finds all object elements that match the Filter criteria.
* <p/>
*
* @param <T> the class type of the Collection elements.
* @param collection the Collection of elements to iterate and filter.
* @param filter the Filter applied to the Collection of elements in search of the matching
* element.
* @return a single element from the Collection that match the criteria of the Filter. If multiple
* elements match the Filter criteria, then this method will return the first one. If no
* element of the Collection matches the criteria of the Filter, then this method returns
* null.
*/
public static <T> T findBy(final Collection<T> collection, final Filter<T> filter) {
for (T element : collection) {
if (filter.accept(element)) {
return element;
}
}
return null;
}
/**
* Removes keys from the Map based on a Filter.
* <p/>
*
* @param <K> the Class type of the key.
* @param <V> the Class type of the value.
* @param map the Map from which to remove key-value pairs based on a Filter.
* @param filter the Filter to apply to the Map entries to ascertain their "value".
* @return the Map with entries filtered by the specified Filter.
* @see java.util.Map
* @see java.util.Map.Entry
* @see org.apache.geode.internal.lang.Filter
*/
public static <K, V> Map<K, V> removeKeys(final Map<K, V> map,
final Filter<Map.Entry<K, V>> filter) {
for (final Iterator<Map.Entry<K, V>> mapEntries = map.entrySet().iterator(); mapEntries
.hasNext();) {
if (!filter.accept(mapEntries.next())) {
mapEntries.remove();
}
}
return map;
}
/**
* Removes keys with null values in the Map.
* <p/>
*
* @param map the Map from which to remove null key-value pairs.
* @return the Map without any null keys or values.
* @see #removeKeys
* @see java.util.Map
*/
public static <K, V> Map<K, V> removeKeysWithNullValues(final Map<K, V> map) {
return removeKeys(map, new Filter<Map.Entry<K, V>>() {
@Override
public boolean accept(final Map.Entry<K, V> entry) {
return (entry.getValue() != null);
}
});
}
/**
* Add all elements of an {@link Enumeration} to a {@link Collection}.
*
* @param collection to add from enumeration.
* @param enumeration to add to collection.
* @return true if collection is modified, otherwise false.
* @since GemFire 8.1
* @see Collection#addAll(Collection)
*/
public static final <T> boolean addAll(final Collection<T> collection,
final Enumeration<T> enumeration) {
if (null == enumeration) {
return false;
}
boolean modified = false;
while (enumeration.hasMoreElements()) {
modified |= collection.add(enumeration.nextElement());
}
return modified;
}
/**
* Construct a new unmodifiable {@link Iterable} backed by the supplied <code>iterable</code>.
*
* {@link Iterable#iterator()} will return an umodifiable {@link Iterator} on which calling
* {@link Iterator#remove()} will throw {@link UnsupportedOperationException}.
*
* @param iterable to wrap as unmodifiable
* @return unmodifiable {@link Iterable}
* @since GemFire 8.1
*/
public static final <T> Iterable<T> unmodifiableIterable(final Iterable<T> iterable) {
return new UnmodifiableIterable<T>(iterable);
}
/**
* Unmodifiable {@link Iterable} in the style of
* {@link Collections#unmodifiableCollection(Collection)}.
*
*
* @since GemFire 8.1
*/
static private class UnmodifiableIterable<T> implements Iterable<T> {
final private Iterable<T> iterable;
private UnmodifiableIterable(final Iterable<T> iterable) {
this.iterable = iterable;
}
@Override
public Iterator<T> iterator() {
return new Iterator<T>() {
final private Iterator<T> iterator = iterable.iterator();
@Override
public boolean hasNext() {
return iterator.hasNext();
}
@Override
public T next() {
return iterator.next();
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
};
}
}
}