直接上代码：
Map<String, String> collect = noWhiteListMap.entrySet().stream().sorted(Comparator.comparing(entry -> entry.getValue().split(",").length,Comparator.reverseOrder())).collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue,(oldValue, newValue) -> oldValue, LinkedHashMap::new));
在java 8中按照此步骤对map进行排序.
- 将 Map 转换为 Stream
- 对其进行排序
- Collect and return a new
LinkedHashMap(保持顺序)
其中 Comparator 接口有两个 comparing 方法
/*** Accepts a function that extracts a sort key from a type {@code T}, and* returns a {@code Comparator<T>} that compares by that sort key using* the specified {@link Comparator}.** <p>The returned comparator is serializable if the specified function* and comparator are both serializable.** @apiNote* For example, to obtain a {@code Comparator} that compares {@code* Person} objects by their last name ignoring case differences,** <pre>{@code* Comparator<Person> cmp = Comparator.comparing(* Person::getLastName,* String.CASE_INSENSITIVE_ORDER);* }</pre>** @param <T> the type of element to be compared* @param <U> the type of the sort key* @param keyExtractor the function used to extract the sort key* @param keyComparator the {@code Comparator} used to compare the sort key* @return a comparator that compares by an extracted key using the* specified {@code Comparator}* @throws NullPointerException if either argument is null* @since 1.8*/public static <T, U> Comparator<T> comparing(Function<? super T, ? extends U> keyExtractor,Comparator<? super U> keyComparator){Objects.requireNonNull(keyExtractor);Objects.requireNonNull(keyComparator);return (Comparator<T> & Serializable)(c1, c2) -> keyComparator.compare(keyExtractor.apply(c1),keyExtractor.apply(c2));}/*** Accepts a function that extracts a {@link java.lang.Comparable* Comparable} sort key from a type {@code T}, and returns a {@code* Comparator<T>} that compares by that sort key.** <p>The returned comparator is serializable if the specified function* is also serializable.** @apiNote* For example, to obtain a {@code Comparator} that compares {@code* Person} objects by their last name,** <pre>{@code* Comparator<Person> byLastName = Comparator.comparing(Person::getLastName);* }</pre>** @param <T> the type of element to be compared* @param <U> the type of the {@code Comparable} sort key* @param keyExtractor the function used to extract the {@link* Comparable} sort key* @return a comparator that compares by an extracted key* @throws NullPointerException if the argument is null* @since 1.8*/public static <T, U extends Comparable<? super U>> Comparator<T> comparing(Function<? super T, ? extends U> keyExtractor){Objects.requireNonNull(keyExtractor);return (Comparator<T> & Serializable)(c1, c2) -> keyExtractor.apply(c1).compareTo(keyExtractor.apply(c2));}
利用 comparing 比较方法传入 比较的函数 和 自定义排序的 如降序 通过 LinkedHashMap 保存顺序