Views.java
/*
* Copyright (c) 2016, 2025 Oracle and/or its affiliates. All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v. 2.0, which is available at
* http://www.eclipse.org/legal/epl-2.0.
*
* This Source Code may also be made available under the following Secondary
* Licenses when the conditions for such availability set forth in the
* Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
* version 2 with the GNU Classpath Exception, which is available at
* https://www.gnu.org/software/classpath/license.html.
*
* SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
*/
package org.glassfish.jersey.internal.util.collection;
import java.util.AbstractMap;
import java.util.AbstractSequentialList;
import java.util.AbstractSet;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.Map;
import java.util.Objects;
import java.util.Set;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Collectors;
/**
* Collections utils, which provide transforming views for {@link List} and {@link Map}.
*
* @author Pavel Bucek
*/
public class Views {
private Views() {
// prevent instantiation.
}
/**
* Create a {@link List} view, which transforms the values of provided original list.
* <p>
* Removing elements from the view is supported, adding and setting isn't and
* throws {@link UnsupportedOperationException} when invoked.
*
* @param originalList original list.
* @param transformer transforming functions.
* @param <T> transformed type parameter.
* @param <R> type of the element from provided list.
* @return transformed list view.
*/
public static <T, R> List<T> listView(List<R> originalList, Function<R, T> transformer) {
return new AbstractSequentialList<T>() {
@Override
public ListIterator<T> listIterator(int index) {
return new ListIterator<T>() {
final ListIterator<R> iterator = originalList.listIterator(index);
@Override
public boolean hasNext() {
return iterator.hasNext();
}
@Override
public T next() {
return transformer.apply(iterator.next());
}
@Override
public boolean hasPrevious() {
return iterator.hasPrevious();
}
@Override
public T previous() {
return transformer.apply(iterator.previous());
}
@Override
public int nextIndex() {
return iterator.nextIndex();
}
@Override
public int previousIndex() {
return iterator.previousIndex();
}
@Override
public void remove() {
iterator.remove();
}
@Override
public void set(T t) {
throw new UnsupportedOperationException("Not supported.");
}
@Override
public void add(T t) {
throw new UnsupportedOperationException("Not supported.");
}
};
}
@Override
public int size() {
return originalList.size();
}
};
}
/**
* Create a {@link Map} view, which transforms the values of provided original map.
* <p>
* Removing elements from the map view is supported, adding and setting isn't and
* throws {@link UnsupportedOperationException} when invoked.
*
* @param originalMap provided map.
* @param valuesTransformer values transformer.
* @param <K> key type.
* @param <V> transformed value type.
* @param <O> original value type.
* @return transformed map view.
*/
public static <K, V, O> Map<K, V> mapView(Map<K, O> originalMap, Function<O, V> valuesTransformer) {
return new KVOMap<K, V, O>(originalMap, valuesTransformer);
}
private static class KVOMap<K, V, O> extends AbstractMap<K, V> {
protected final Map<K, O> originalMap;
protected final Function<O, V> valuesTransformer;
private KVOMap(Map<K, O> originalMap, Function<O, V> valuesTransformer) {
this.originalMap = originalMap;
this.valuesTransformer = valuesTransformer;
}
@Override
public Set<Entry<K, V>> entrySet() {
return new AbstractSet<Entry<K, V>>() {
Set<Entry<K, O>> originalSet = originalMap.entrySet();
Iterator<Entry<K, O>> original = originalSet.iterator();
@Override
public Iterator<Entry<K, V>> iterator() {
return new Iterator<Entry<K, V>>() {
@Override
public boolean hasNext() {
return original.hasNext();
}
@Override
public Entry<K, V> next() {
Entry<K, O> next = original.next();
return new Entry<K, V>() {
@Override
public K getKey() {
return next.getKey();
}
@Override
public V getValue() {
return valuesTransformer.apply(next.getValue());
}
@Override
public V setValue(V value) {
return KVOMap.this.setValue(next, value);
}
};
}
@Override
public void remove() {
original.remove();
}
};
}
@Override
public int size() {
return originalSet.size();
}
};
}
protected V setValue(Map.Entry<K, O> entry, V value) {
throw new UnsupportedOperationException("Not supported.");
}
}
/**
* Create a {@link Map} view, which transforms the values of provided original map.
* <p>
*
* @param originalMap provided map.
* @param valuesTransformer values transformer.
* @return transformed map view.
*/
public static Map<String, List<String>> mapObjectToStringView(Map<String, List<Object>> originalMap,
Function<List<Object>, List<String>> valuesTransformer) {
return new ObjectToStringMap(originalMap, valuesTransformer);
}
private static class ObjectToStringMap extends KVOMap<String, List<String>, List<Object>> {
private ObjectToStringMap(Map<String, List<Object>> originalMap, Function<List<Object>, List<String>> valuesTransformer) {
super(originalMap, valuesTransformer);
}
@Override
protected List<String> setValue(Entry<String, List<Object>> entry, List<String> value) {
@SuppressWarnings("unchecked")
final List<Object> old = entry.setValue((List<Object>) (List<?>) value);
return valuesTransformer.apply(old);
}
@Override
public List<String> put(String key, List<String> value) {
@SuppressWarnings("unchecked")
final List<Object> old = originalMap.put(key, (List<Object>) (List<?>) value);
return valuesTransformer.apply(old);
}
@Override
public boolean containsKey(Object key) {
Iterator<Entry<String, List<String>>> i = entrySet().iterator();
if (key == null) {
while (i.hasNext()) {
Entry<String, List<String>> e = i.next();
if (e.getKey() == null) {
return true;
}
}
} else {
while (i.hasNext()) {
Entry<String, List<String>> e = i.next();
if (((String) key).equalsIgnoreCase(e.getKey())) {
return true;
}
}
}
return false;
}
@Override
public List<String> get(Object key) {
Iterator<Entry<String, List<String>>> i = entrySet().iterator();
if (key == null) {
while (i.hasNext()) {
Entry<String, List<String>> e = i.next();
if (e.getKey() == null) {
return e.getValue();
}
}
} else {
while (i.hasNext()) {
Entry<String, List<String>> e = i.next();
if (((String) key).equalsIgnoreCase(e.getKey())) {
return e.getValue();
}
}
}
return null;
}
@Override
public List<String> remove(Object key) {
Iterator<Entry<String, List<String>>> i = entrySet().iterator();
Entry<String, List<String>> correctEntry = null;
if (key == null) {
while (correctEntry == null && i.hasNext()) {
Entry<String, List<String>> e = i.next();
if (e.getKey() == null) {
correctEntry = e;
}
}
} else {
while (correctEntry == null && i.hasNext()) {
Entry<String, List<String>> e = i.next();
if (((String) key).equalsIgnoreCase(e.getKey())) {
correctEntry = e;
}
}
}
List<String> oldValue = null;
if (correctEntry != null) {
oldValue = correctEntry.getValue();
i.remove();
}
return oldValue;
}
}
/**
* Create a view of an union of provided sets.
* <p>
* View is updated whenever any of the provided set changes.
*
* @param set1 first set.
* @param set2 second set.
* @param <E> set item type.
* @return union view of given sets.
*/
public static <E> Set<E> setUnionView(final Set<? extends E> set1, final Set<? extends E> set2) {
Objects.requireNonNull(set1, "set1");
Objects.requireNonNull(set2, "set2");
return new AbstractSet<E>() {
@Override
public Iterator<E> iterator() {
return getUnion(set1, set2).iterator();
}
@Override
public int size() {
return getUnion(set1, set2).size();
}
private Set<E> getUnion(Set<? extends E> set1, Set<? extends E> set2) {
HashSet<E> hashSet = new HashSet<>(set1);
hashSet.addAll(set2);
return hashSet;
}
};
}
/**
* Create a view of a difference of provided sets, i.e. the diff filters out from the first set the items included
* in the second set.
* <p>
* View is updated whenever any of the provided set changes.
*
* @param set1 first set.
* @param set2 second set.
* @param <E> set item type.
* @return view that is a difference of given sets.
*/
public static <E> Set<E> setDiffView(final Set<? extends E> set1, final Set<? extends E> set2) {
Objects.requireNonNull(set1, "set1");
Objects.requireNonNull(set2, "set2");
return new AbstractSet<E>() {
@Override
public Iterator<E> iterator() {
return getDiff(set1, set2).iterator();
}
@Override
public int size() {
return getDiff(set1, set2).size();
}
private Set<E> getDiff(Set<? extends E> set1, Set<? extends E> set2) {
HashSet<E> hashSet = new HashSet<>();
hashSet.addAll(set1);
hashSet.addAll(set2);
return hashSet.stream().filter(new Predicate<E>() {
@Override
public boolean test(E e) {
return set1.contains(e) && !set2.contains(e);
}
}).collect(Collectors.toSet());
}
};
}
}