jdk8之map排序

public class  {

    
     * JDK8
     * 按照Key排序
     *
     * @param map map数据
     * @param asc 是否升序
     * @param <K> Key
     * @param <V> Value
     * @return Map<K, V>
     */
    private static <K extends Comparable<? super K>, V> Map<K, V> sortByKey(Map<K, V> map, boolean asc) {
        Map<K, V> result = new LinkedHashMap<>();
        Stream<Map.Entry<K, V>> stream = map.entrySet().stream();
        if (asc) {
            stream.sorted(Map.Entry.comparingByKey()).forEachOrdered(e -> result.put(e.getKey(), e.getValue()));
        } else {
            stream.sorted(Map.Entry.<K, V>comparingByKey().reversed()).forEachOrdered(e -> result.put(e.getKey(), e.getValue()));
        }
        return result;
    }

    
     * JDK8
     * 按照Value排序
     *
     * @param map map数据
     * @param asc 是否升序
     * @param <K> Key
     * @param <V> Value
     * @return Map<K, V>
     */
    private static <K, V extends Comparable<? super V>> Map<K, V> sortByValue(Map<K, V> map, boolean asc) {
        Map<K, V> result = new LinkedHashMap<>();
        Stream<Map.Entry<K, V>> stream = map.entrySet().stream();
        if (asc) //升序
        {
            stream.sorted(Map.Entry.comparingByValue()).forEachOrdered(e -> result.put(e.getKey(), e.getValue()));
        } else //降序
        {
            stream.sorted(Map.Entry.<K, V>comparingByValue().reversed()).forEachOrdered(e -> result.put(e.getKey(), e.getValue()));
        }
        return result;
    }

    
     * 使用 Map按key进行排序
     */
    public static String sortMapByKey(HashMap<String, String> map) {

        Set<String> keySet = map.keySet();

        String[] keyArray = keySet.toArray(new String[0]);

        Arrays.sort(keyArray);
        StringBuilder sb = new StringBuilder();
        for (String k : keyArray) {
            if (map.get(k).trim().length() > 0) // 参数值为空，则不参与签名
                sb.append(k).append("=").append(map.get(k).trim()).append("&");
        }
        return sb.toString().substring(0, sb.length() - 1);
    }

    public static void main(String[] args) {

        Map<String, Integer> map = new LinkedHashMap<>();

        map.put("b", 44);
        map.put("a", 22);
        map.put("c", 11);

        System.out.println(map);

        System.out.println(sortByKey(map, true));

        System.out.println(sortByValue(map, false));
    }
}