io.jsonwebtoken.lang.Collections Maven / Gradle / Ivy
/*
* Copyright (C) 2014 jsonwebtoken.io
*
* 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 io.jsonwebtoken.lang;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import java.util.Set;
/**
* Utility methods for working with {@link Collection}s, {@link List}s, {@link Set}s, and {@link Maps}.
*/
@SuppressWarnings({"unused", "rawtypes"})
public final class Collections {
private Collections() {
} //prevent instantiation
/**
* Returns a type-safe immutable empty {@code List}.
*
* @param list element type
* @return a type-safe immutable empty {@code List}.
*/
public static List emptyList() {
return java.util.Collections.emptyList();
}
/**
* Returns a type-safe immutable empty {@code Set}.
*
* @param set element type
* @return a type-safe immutable empty {@code Set}.
*/
@SuppressWarnings("unused")
public static Set emptySet() {
return java.util.Collections.emptySet();
}
/**
* Returns a type-safe immutable empty {@code Map}.
*
* @param map key type
* @param map value type
* @return a type-safe immutable empty {@code Map}.
*/
@SuppressWarnings("unused")
public static Map emptyMap() {
return java.util.Collections.emptyMap();
}
/**
* Returns a type-safe immutable {@code List} containing the specified array elements.
*
* @param elements array elements to include in the list
* @param list element type
* @return a type-safe immutable {@code List} containing the specified array elements.
*/
@SafeVarargs
public static List of(T... elements) {
if (elements == null || elements.length == 0) {
return java.util.Collections.emptyList();
}
return java.util.Collections.unmodifiableList(Arrays.asList(elements));
}
/**
* Returns the specified collection as a {@link Set} instance.
*
* @param c the collection to represent as a set
* @param collection element type
* @return a type-safe immutable {@code Set} containing the specified collection elements.
* @since 0.12.0
*/
public static Set asSet(Collection c) {
if (c instanceof Set) {
return (Set) c;
}
if (isEmpty(c)) {
return java.util.Collections.emptySet();
}
return java.util.Collections.unmodifiableSet(new LinkedHashSet<>(c));
}
/**
* Returns a type-safe immutable {@code Set} containing the specified array elements.
*
* @param elements array elements to include in the set
* @param set element type
* @return a type-safe immutable {@code Set} containing the specified array elements.
*/
@SafeVarargs
public static Set setOf(T... elements) {
if (elements == null || elements.length == 0) {
return java.util.Collections.emptySet();
}
Set set = new LinkedHashSet<>(Arrays.asList(elements));
return immutable(set);
}
/**
* Shorter null-safe convenience alias for {@link java.util.Collections#unmodifiableList(List)} so both classes
* don't need to be imported.
*
* @param m map to wrap in an immutable/unmodifiable collection
* @param map key type
* @param map value type
* @return an immutable wrapper for {@code m}.
* @since 0.12.0
*/
public static Map immutable(Map m) {
return m != null ? java.util.Collections.unmodifiableMap(m) : null;
}
/**
* Shorter null-safe convenience alias for {@link java.util.Collections#unmodifiableSet(Set)} so both classes don't
* need to be imported.
*
* @param set set to wrap in an immutable Set
* @param set element type
* @return an immutable wrapper for {@code set}
*/
public static Set immutable(Set set) {
return set != null ? java.util.Collections.unmodifiableSet(set) : null;
}
/**
* Shorter null-safe convenience alias for {@link java.util.Collections#unmodifiableList(List)} so both classes
* don't need to be imported.
*
* @param list list to wrap in an immutable List
* @param list element type
* @return an immutable wrapper for {@code list}
*/
public static List immutable(List list) {
return list != null ? java.util.Collections.unmodifiableList(list) : null;
}
/**
* Null-safe factory method that returns an immutable/unmodifiable view of the specified collection instance.
* Works for {@link List}, {@link Set} and {@link Collection} arguments.
*
* @param c collection to wrap in an immutable/unmodifiable collection
* @param type of collection
* @param type of elements in the collection
* @return an immutable wrapper for {@code l}.
* @since 0.12.0
*/
@SuppressWarnings("unchecked")
public static > C immutable(C c) {
if (c == null) {
return null;
} else if (c instanceof Set) {
return (C) java.util.Collections.unmodifiableSet((Set) c);
} else if (c instanceof List) {
return (C) java.util.Collections.unmodifiableList((List) c);
} else {
return (C) java.util.Collections.unmodifiableCollection(c);
}
}
/**
* Returns a non-null set, either {@code s} if it is not null, or {@link #emptySet()} otherwise.
*
* @param s the set to check for null
* @param type of elements in the set
* @return a non-null set, either {@code s} if it is not null, or {@link #emptySet()} otherwise.
* @since 0.12.0
*/
public static Set nullSafe(Set s) {
return s == null ? Collections.emptySet() : s;
}
/**
* Returns a non-null collection, either {@code c} if it is not null, or {@link #emptyList()} otherwise.
*
* @param c the collection to check for null
* @param type of elements in the collection
* @return a non-null collection, either {@code c} if it is not null, or {@link #emptyList()} otherwise.
* @since 0.12.0
*/
public static Collection nullSafe(Collection c) {
return c == null ? Collections.emptyList() : c;
}
/**
* Return true if the supplied Collection is null
* or empty. Otherwise, return false.
*
* @param collection the Collection to check
* @return whether the given Collection is empty
*/
public static boolean isEmpty(Collection collection) {
return size(collection) == 0;
}
/**
* Returns the collection's size or {@code 0} if the collection is {@code null}.
*
* @param collection the collection to check.
* @return the collection's size or {@code 0} if the collection is {@code null}.
* @since 0.9.2
*/
public static int size(Collection collection) {
return collection == null ? 0 : collection.size();
}
/**
* Returns the map's size or {@code 0} if the map is {@code null}.
*
* @param map the map to check
* @return the map's size or {@code 0} if the map is {@code null}.
* @since 0.9.2
*/
public static int size(Map map) {
return map == null ? 0 : map.size();
}
/**
* Return true if the supplied Map is null
* or empty. Otherwise, return false.
*
* @param map the Map to check
* @return whether the given Map is empty
*/
public static boolean isEmpty(Map map) {
return size(map) == 0;
}
/**
* Convert the supplied array into a List. A primitive array gets
* converted into a List of the appropriate wrapper type.
* A null source value will be converted to an
* empty List.
*
* @param source the (potentially primitive) array
* @return the converted List result
* @see Objects#toObjectArray(Object)
*/
public static List arrayToList(Object source) {
return Arrays.asList(Objects.toObjectArray(source));
}
/**
* Concatenate the specified set with the specified array elements, resulting in a new {@link LinkedHashSet} with
* the array elements appended to the end of the existing Set.
*
* @param c the set to append to
* @param elements the array elements to append to the end of the set
* @param set element type
* @return a new {@link LinkedHashSet} with the array elements appended to the end of the original set.
*/
@SafeVarargs
public static Set concat(Set c, T... elements) {
int size = Math.max(1, Collections.size(c) + io.jsonwebtoken.lang.Arrays.length(elements));
Set set = new LinkedHashSet<>(size);
set.addAll(c);
java.util.Collections.addAll(set, elements);
return immutable(set);
}
/**
* Merge the given array into the given Collection.
*
* @param array the array to merge (may be null)
* @param collection the target Collection to merge the array into
*/
@SuppressWarnings("unchecked")
public static void mergeArrayIntoCollection(Object array, Collection collection) {
if (collection == null) {
throw new IllegalArgumentException("Collection must not be null");
}
Object[] arr = Objects.toObjectArray(array);
java.util.Collections.addAll(collection, arr);
}
/**
* Merge the given Properties instance into the given Map,
* copying all properties (key-value pairs) over.
* Uses Properties.propertyNames() to even catch
* default properties linked into the original Properties instance.
*
* @param props the Properties instance to merge (may be null)
* @param map the target Map to merge the properties into
*/
@SuppressWarnings("unchecked")
public static void mergePropertiesIntoMap(Properties props, Map map) {
if (map == null) {
throw new IllegalArgumentException("Map must not be null");
}
if (props != null) {
for (Enumeration en = props.propertyNames(); en.hasMoreElements(); ) {
String key = (String) en.nextElement();
Object value = props.getProperty(key);
if (value == null) {
// Potentially a non-String value...
value = props.get(key);
}
map.put(key, value);
}
}
}
/**
* Check whether the given Iterator contains the given element.
*
* @param iterator the Iterator to check
* @param element the element to look for
* @return true if found, false else
*/
public static boolean contains(Iterator iterator, Object element) {
if (iterator != null) {
while (iterator.hasNext()) {
Object candidate = iterator.next();
if (Objects.nullSafeEquals(candidate, element)) {
return true;
}
}
}
return false;
}
/**
* Check whether the given Enumeration contains the given element.
*
* @param enumeration the Enumeration to check
* @param element the element to look for
* @return true if found, false else
*/
public static boolean contains(Enumeration enumeration, Object element) {
if (enumeration != null) {
while (enumeration.hasMoreElements()) {
Object candidate = enumeration.nextElement();
if (Objects.nullSafeEquals(candidate, element)) {
return true;
}
}
}
return false;
}
/**
* Check whether the given Collection contains the given element instance.
*
Enforces the given instance to be present, rather than returning
* true for an equal element as well.
*
* @param collection the Collection to check
* @param element the element to look for
* @return true if found, false else
*/
public static boolean containsInstance(Collection collection, Object element) {
if (collection != null) {
for (Object candidate : collection) {
if (candidate == element) {
return true;
}
}
}
return false;
}
/**
* Return true if any element in 'candidates' is
* contained in 'source'; otherwise returns false.
*
* @param source the source Collection
* @param candidates the candidates to search for
* @return whether any of the candidates has been found
*/
public static boolean containsAny(Collection source, Collection candidates) {
if (isEmpty(source) || isEmpty(candidates)) {
return false;
}
for (Object candidate : candidates) {
if (source.contains(candidate)) {
return true;
}
}
return false;
}
/**
* Return the first element in 'candidates' that is contained in
* 'source'. If no element in 'candidates' is present in
* 'source' returns null. Iteration order is
* {@link Collection} implementation specific.
*
* @param source the source Collection
* @param candidates the candidates to search for
* @return the first present object, or null if not found
*/
public static Object findFirstMatch(Collection source, Collection candidates) {
if (isEmpty(source) || isEmpty(candidates)) {
return null;
}
for (Object candidate : candidates) {
if (source.contains(candidate)) {
return candidate;
}
}
return null;
}
/**
* Find a single value of the given type in the given Collection.
*
* @param collection the Collection to search
* @param type the type to look for
* @param the generic type parameter for {@code type}
* @return a value of the given type found if there is a clear match,
* or null if none or more than one such value found
*/
@SuppressWarnings("unchecked")
public static T findValueOfType(Collection collection, Class type) {
if (isEmpty(collection)) {
return null;
}
T value = null;
for (Object element : collection) {
if (type == null || type.isInstance(element)) {
if (value != null) {
// More than one value found... no clear single value.
return null;
}
value = (T) element;
}
}
return value;
}
/**
* Find a single value of one of the given types in the given Collection:
* searching the Collection for a value of the first type, then
* searching for a value of the second type, etc.
*
* @param collection the collection to search
* @param types the types to look for, in prioritized order
* @return a value of one of the given types found if there is a clear match,
* or null if none or more than one such value found
*/
public static Object findValueOfType(Collection collection, Class[] types) {
if (isEmpty(collection) || Objects.isEmpty(types)) {
return null;
}
for (Class type : types) {
Object value = findValueOfType(collection, type);
if (value != null) {
return value;
}
}
return null;
}
/**
* Determine whether the given Collection only contains a single unique object.
*
* @param collection the Collection to check
* @return true if the collection contains a single reference or
* multiple references to the same instance, false else
*/
public static boolean hasUniqueObject(Collection collection) {
if (isEmpty(collection)) {
return false;
}
boolean hasCandidate = false;
Object candidate = null;
for (Object elem : collection) {
if (!hasCandidate) {
hasCandidate = true;
candidate = elem;
} else if (candidate != elem) {
return false;
}
}
return true;
}
/**
* Find the common element type of the given Collection, if any.
*
* @param collection the Collection to check
* @return the common element type, or null if no clear
* common type has been found (or the collection was empty)
*/
public static Class findCommonElementType(Collection collection) {
if (isEmpty(collection)) {
return null;
}
Class candidate = null;
for (Object val : collection) {
if (val != null) {
if (candidate == null) {
candidate = val.getClass();
} else if (candidate != val.getClass()) {
return null;
}
}
}
return candidate;
}
/**
* Marshal the elements from the given enumeration into an array of the given type.
* Enumeration elements must be assignable to the type of the given array. The array
* returned will be a different instance than the array given.
*
* @param enumeration the collection to convert to an array
* @param array an array instance that matches the type of array to return
* @param the element type of the array that will be created
* @param the element type contained within the enumeration.
* @return a new array of type {@code A} that contains the elements in the specified {@code enumeration}.
*/
public static A[] toArray(Enumeration enumeration, A[] array) {
ArrayList elements = new ArrayList<>();
while (enumeration.hasMoreElements()) {
elements.add(enumeration.nextElement());
}
return elements.toArray(array);
}
/**
* Adapt an enumeration to an iterator.
*
* @param enumeration the enumeration
* @param the type of elements in the enumeration
* @return the iterator
*/
public static Iterator toIterator(Enumeration enumeration) {
return new EnumerationIterator<>(enumeration);
}
/**
* Iterator wrapping an Enumeration.
*/
private static class EnumerationIterator implements Iterator {
private final Enumeration enumeration;
public EnumerationIterator(Enumeration enumeration) {
this.enumeration = enumeration;
}
public boolean hasNext() {
return this.enumeration.hasMoreElements();
}
public E next() {
return this.enumeration.nextElement();
}
public void remove() throws UnsupportedOperationException {
throw new UnsupportedOperationException("Not supported");
}
}
}