操作集合
public class CollectionUtils {
public static boolean containsAny(Object source, Object... targets) {
return asList(targets).contains(source);
}
public static boolean isAnyEmpty(Collection<?>... collections) {
return Arrays.stream(collections).anyMatch(CollectionUtil::isEmpty);
}
public static <T> boolean anyMatch(Collection<T> from, Predicate<T> predicate) {
return from.stream().anyMatch(predicate);
}
public static <T> List<T> filterList(Collection<T> from, Predicate<T> predicate) {
if (CollUtil.isEmpty(from)) {
return new ArrayList<>();
}
return from.stream().filter(predicate).collect(Collectors.toList());
}
public static <T, R> List<T> distinct(Collection<T> from, Function<T, R> keyMapper) {
if (CollUtil.isEmpty(from)) {
return new ArrayList<>();
}
return distinct(from, keyMapper, (t1, t2) -> t1);
}
public static <T, R> List<T> distinct(Collection<T> from, Function<T, R> keyMapper, BinaryOperator<T> cover) {
if (CollUtil.isEmpty(from)) {
return new ArrayList<>();
}
return new ArrayList<>(convertMap(from, keyMapper, Function.identity(), cover).values());
}
public static <T, U> List<U> convertList(T[] from, Function<T, U> func) {
if (ArrayUtil.isEmpty(from)) {
return new ArrayList<>();
}
return convertList(Arrays.asList(from), func);
}
public static <T, U> List<U> convertList(Collection<T> from, Function<T, U> func) {
if (CollUtil.isEmpty(from)) {
return new ArrayList<>();
}
return from.stream().map(func).filter(Objects::nonNull).collect(Collectors.toList());
}
public static <T, U> List<U> convertList(Collection<T> from, Function<T, U> func, Predicate<T> filter) {
if (CollUtil.isEmpty(from)) {
return new ArrayList<>();
}
return from.stream().filter(filter).map(func).filter(Objects::nonNull).collect(Collectors.toList());
}
public static <T, U> List<U> convertListByFlatMap(Collection<T> from,
Function<T, ? extends Stream<? extends U>> func) {
if (CollUtil.isEmpty(from)) {
return new ArrayList<>();
}
return from.stream().flatMap(func).filter(Objects::nonNull).collect(Collectors.toList());
}
public static <T, U, R> List<R> convertListByFlatMap(Collection<T> from,
Function<? super T, ? extends U> mapper,
Function<U, ? extends Stream<? extends R>> func) {
if (CollUtil.isEmpty(from)) {
return new ArrayList<>();
}
return from.stream().map(mapper).flatMap(func).filter(Objects::nonNull).collect(Collectors.toList());
}
public static <K, V> List<V> mergeValuesFromMap(Map<K, List<V>> map) {
return map.values()
.stream()
.flatMap(List::stream)
.collect(Collectors.toList());
}
public static <T, U> Set<U> convertSet(Collection<T> from, Function<T, U> func) {
if (CollUtil.isEmpty(from)) {
return new HashSet<>();
}
return from.stream().map(func).filter(Objects::nonNull).collect(Collectors.toSet());
}
public static <T, U> Set<U> convertSet(Collection<T> from, Function<T, U> func, Predicate<T> filter) {
if (CollUtil.isEmpty(from)) {
return new HashSet<>();
}
return from.stream().filter(filter).map(func).filter(Objects::nonNull).collect(Collectors.toSet());
}
public static <T, K> Map<K, T> convertMapByFilter(Collection<T> from, Predicate<T> filter, Function<T, K> keyFunc) {
if (CollUtil.isEmpty(from)) {
return new HashMap<>();
}
return from.stream().filter(filter).collect(Collectors.toMap(keyFunc, v -> v));
}
public static <T, U> Set<U> convertSetByFlatMap(Collection<T> from,
Function<T, ? extends Stream<? extends U>> func) {
if (CollUtil.isEmpty(from)) {
return new HashSet<>();
}
return from.stream().flatMap(func).filter(Objects::nonNull).collect(Collectors.toSet());
}
public static <T, U, R> Set<R> convertSetByFlatMap(Collection<T> from,
Function<? super T, ? extends U> mapper,
Function<U, ? extends Stream<? extends R>> func) {
if (CollUtil.isEmpty(from)) {
return new HashSet<>();
}
return from.stream().map(mapper).flatMap(func).filter(Objects::nonNull).collect(Collectors.toSet());
}
public static <T, K> Map<K, T> convertMap(Collection<T> from, Function<T, K> keyFunc) {
if (CollUtil.isEmpty(from)) {
return new HashMap<>();
}
return convertMap(from, keyFunc, Function.identity());
}
public static <T, K> Map<K, T> convertMap(Collection<T> from, Function<T, K> keyFunc, Supplier<? extends Map<K, T>> supplier) {
if (CollUtil.isEmpty(from)) {
return supplier.get();
}
return convertMap(from, keyFunc, Function.identity(), supplier);
}
public static <T, K, V> Map<K, V> convertMap(Collection<T> from, Function<T, K> keyFunc, Function<T, V> valueFunc) {
if (CollUtil.isEmpty(from)) {
return new HashMap<>();
}
return convertMap(from, keyFunc, valueFunc, (v1, v2) -> v1);
}
public static <T, K, V> Map<K, V> convertMap(Collection<T> from, Function<T, K> keyFunc, Function<T, V> valueFunc, BinaryOperator<V> mergeFunction) {
if (CollUtil.isEmpty(from)) {
return new HashMap<>();
}
return convertMap(from, keyFunc, valueFunc, mergeFunction, HashMap::new);
}
public static <T, K, V> Map<K, V> convertMap(Collection<T> from, Function<T, K> keyFunc, Function<T, V> valueFunc, Supplier<? extends Map<K, V>> supplier) {
if (CollUtil.isEmpty(from)) {
return supplier.get();
}
return convertMap(from, keyFunc, valueFunc, (v1, v2) -> v1, supplier);
}
public static <T, K, V> Map<K, V> convertMap(Collection<T> from, Function<T, K> keyFunc, Function<T, V> valueFunc, BinaryOperator<V> mergeFunction, Supplier<? extends Map<K, V>> supplier) {
if (CollUtil.isEmpty(from)) {
return new HashMap<>();
}
return from.stream().collect(Collectors.toMap(keyFunc, valueFunc, mergeFunction, supplier));
}
public static <T, K> Map<K, List<T>> convertMultiMap(Collection<T> from, Function<T, K> keyFunc) {
if (CollUtil.isEmpty(from)) {
return new HashMap<>();
}
return from.stream().collect(Collectors.groupingBy(keyFunc, Collectors.mapping(t -> t, Collectors.toList())));
}
public static <T, K, V> Map<K, List<V>> convertMultiMap(Collection<T> from, Function<T, K> keyFunc, Function<T, V> valueFunc) {
if (CollUtil.isEmpty(from)) {
return new HashMap<>();
}
return from.stream()
.collect(Collectors.groupingBy(keyFunc, Collectors.mapping(valueFunc, Collectors.toList())));
}
// 暂时没想好名字，先以 2 结尾噶
public static <T, K, V> Map<K, Set<V>> convertMultiMap2(Collection<T> from, Function<T, K> keyFunc, Function<T, V> valueFunc) {
if (CollUtil.isEmpty(from)) {
return new HashMap<>();
}
return from.stream().collect(Collectors.groupingBy(keyFunc, Collectors.mapping(valueFunc, Collectors.toSet())));
}
public static <T, K> Map<K, T> convertImmutableMap(Collection<T> from, Function<T, K> keyFunc) {
if (CollUtil.isEmpty(from)) {
return Collections.emptyMap();
}
ImmutableMap.Builder<K, T> builder = ImmutableMap.builder();
from.forEach(item -> builder.put(keyFunc.apply(item), item));
return builder.build();
}
/**
* 对比老、新两个列表，找出新增、修改、删除的数据
*
* @param oldList 老列表
* @param newList 新列表
* @param sameFunc 对比函数，返回 true 表示相同，返回 false 表示不同
* 注意，same 是通过每个元素的“标识”，判断它们是不是同一个数据
* @return [新增列表、修改列表、删除列表]
*/
public static <T> List<List<T>> diffList(Collection<T> oldList, Collection<T> newList,
BiFunction<T, T, Boolean> sameFunc) {
List<T> createList = new LinkedList<>(newList); // 默认都认为是新增的，后续会进行移除
List<T> updateList = new ArrayList<>();
List<T> deleteList = new ArrayList<>();
// 通过以 oldList 为主遍历，找出 updateList 和 deleteList
for (T oldObj : oldList) {
// 1. 寻找是否有匹配的
T foundObj = null;
for (Iterator<T> iterator = createList.iterator(); iterator.hasNext(); ) {
T newObj = iterator.next();
// 1.1 不匹配，则直接跳过
if (!sameFunc.apply(oldObj, newObj)) {
continue;
}
// 1.2 匹配，则移除，并结束寻找
iterator.remove();
foundObj = newObj;
break;
}
// 2. 匹配添加到 updateList；不匹配则添加到 deleteList 中
if (foundObj != null) {
updateList.add(foundObj);
} else {
deleteList.add(oldObj);
}
}
return asList(createList, updateList, deleteList);
}
public static boolean containsAny(Collection<?> source, Collection<?> candidates) {
return org.springframework.util.CollectionUtils.containsAny(source, candidates);
}
public static <T> T getFirst(List<T> from) {
return !CollectionUtil.isEmpty(from) ? from.get(0) : null;
}
public static <T> T findFirst(List<T> from, Predicate<T> predicate) {
return findFirst(from, predicate, Function.identity());
}
public static <T, U> U findFirst(List<T> from, Predicate<T> predicate, Function<T, U> func) {
if (CollUtil.isEmpty(from)) {
return null;
}
return from.stream().filter(predicate).findFirst().map(func).orElse(null);
}
public static <T, V extends Comparable<? super V>> V getMaxValue(Collection<T> from, Function<T, V> valueFunc) {
if (CollUtil.isEmpty(from)) {
return null;
}
assert !from.isEmpty(); // 断言，避免告警
T t = from.stream().max(Comparator.comparing(valueFunc)).get();
return valueFunc.apply(t);
}
public static <T, V extends Comparable<? super V>> V getMinValue(List<T> from, Function<T, V> valueFunc) {
if (CollUtil.isEmpty(from)) {
return null;
}
assert from.size() > 0; // 断言，避免告警
T t = from.stream().min(Comparator.comparing(valueFunc)).get();
return valueFunc.apply(t);
}
public static <T, V extends Comparable<? super V>> V getSumValue(List<T> from, Function<T, V> valueFunc,
BinaryOperator<V> accumulator) {
if (CollUtil.isEmpty(from)) {
return null;
}
assert from.size() > 0; // 断言，避免告警
return from.stream().map(valueFunc).reduce(accumulator).get();
}
public static <T> void addIfNotNull(Collection<T> coll, T item) {
if (item == null) {
return;
}
coll.add(item);
}
public static <T> Collection<T> singleton(T deptId) {
return deptId == null ? Collections.emptyList() : Collections.singleton(deptId);
}
}
用法如下，简化一些较简单的stream流操作
Set<String> codegenColumnNames = convertSet(codegenColumns, CodegenColumnDO::getColumnName);
MapUtils，操作map
public class MapUtils {
/**
* 从哈希表表中，获得 keys 对应的所有 value 数组
*
* @param multimap 哈希表
* @param keys keys
* @return value 数组
*/
public static <K, V> List<V> getList(Multimap<K, V> multimap, Collection<K> keys) {
List<V> result = new ArrayList<>();
keys.forEach(k -> {
Collection<V> values = multimap.get(k);
if (CollectionUtil.isEmpty(values)) {
return;
}
result.addAll(values);
});
return result;
}
/**
* 从哈希表查找到 key 对应的 value，然后进一步处理
* 注意，如果查找到的 value 为 null 时，不进行处理
*
* @param map 哈希表
* @param key key
* @param consumer 进一步处理的逻辑
*/
public static <K, V> void findAndThen(Map<K, V> map, K key, Consumer<V> consumer) {
if (CollUtil.isEmpty(map)) {
return;
}
V value = map.get(key);
if (value == null) {
return;
}
consumer.accept(value);
}
public static <K, V> Map<K, V> convertMap(List<KeyValue<K, V>> keyValues) {
Map<K, V> map = Maps.newLinkedHashMapWithExpectedSize(keyValues.size());
keyValues.forEach(keyValue -> map.put(keyValue.getKey(), keyValue.getValue()));
return map;
}
}
使用案例：找到value进行其他操作
MapUtils.findAndThen(userMap,NumberUtils.parseLong(assignee),
assignUser-> bpmTaskSubSignRespVO.setAssigneeUser(convert3(assignUser)));
标签：Function,return,stream,流等,编程,Collection,static,isEmpty,public From： https://www.cnblogs.com/jiutang001/p/18233280