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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.Set;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Collectors;
import static org.glassfish.jersey.internal.guava.Preconditions.checkNotNull;
/**
* Collections utils, which provide transforming views for {@link List} and {@link Map}.
*
* @author Pavel Bucek (pavel.bucek at oracle.com)
*/
public class Views {
private Views() {
// prevent instantiation.
}
/**
* Create a {@link List} view, which transforms the values of provided original list.
*
* 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 transformed type parameter.
* @param type of the element from provided list.
* @return transformed list view.
*/
public static List listView(List originalList, Function transformer) {
return new AbstractSequentialList() {
@Override
public ListIterator listIterator(int index) {
return new ListIterator() {
final ListIterator 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.
*
* 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 key type.
* @param transformed value type.
* @param original value type.
* @return transformed map view.
*/
public static Map mapView(Map originalMap, Function valuesTransformer) {
return new AbstractMap() {
@Override
public Set> entrySet() {
return new AbstractSet>() {
Set> originalSet = originalMap.entrySet();
Iterator> original = originalSet.iterator();
@Override
public Iterator> iterator() {
return new Iterator>() {
@Override
public boolean hasNext() {
return original.hasNext();
}
@Override
public Entry next() {
Entry next = original.next();
return new Entry() {
@Override
public K getKey() {
return next.getKey();
}
@Override
public V getValue() {
return valuesTransformer.apply(next.getValue());
}
@Override
public V setValue(V value) {
throw new UnsupportedOperationException("Not supported.");
}
};
}
@Override
public void remove() {
original.remove();
}
};
}
@Override
public int size() {
return originalSet.size();
}
};
}
};
}
/**
* Create a view of an union of provided sets.
*
* View is updated whenever any of the provided set changes.
*
* @param set1 first set.
* @param set2 second set.
* @param set item type.
* @return union view of given sets.
*/
public static Set setUnionView(final Set set1, final Set set2) {
checkNotNull(set1, "set1");
checkNotNull(set2, "set2");
return new AbstractSet() {
@Override
public Iterator iterator() {
return getUnion(set1, set2).iterator();
}
@Override
public int size() {
return getUnion(set1, set2).size();
}
private Set getUnion(Set set1, Set set2) {
HashSet hashSet = new HashSet<>(set1);
hashSet.addAll(set2);
return hashSet;
}
};
}
/**
* Create a view of a difference of provided sets.
*
* View is updated whenever any of the provided set changes.
*
* @param set1 first set.
* @param set2 second set.
* @param set item type.
* @return union view of given sets.
*/
public static Set setDiffView(final Set set1, final Set set2) {
checkNotNull(set1, "set1");
checkNotNull(set2, "set2");
return new AbstractSet() {
@Override
public Iterator iterator() {
return getDiff(set1, set2).iterator();
}
@Override
public int size() {
return getDiff(set1, set2).size();
}
private Set getDiff(Set set1, Set set2) {
HashSet hashSet = new HashSet<>();
hashSet.addAll(set1);
hashSet.addAll(set2);
return hashSet.stream().filter(new Predicate() {
@Override
public boolean test(E e) {
return set1.contains(e) && !set2.contains(e);
}
}).collect(Collectors.toSet());
}
};
}
}