應用場景（一）：

    1.對list<map>中map中某個指定的key的value的去重，得到新的list：去除了重複出現指定key的value值得map

示例：

                要求：過濾掉電話相同的map

                List<Map<String, Object>> mapList = new ArrayList<Map<String, Object>>();
Map<String, Object> mapStr1 = new HashMap<String, Object>();
mapStr1.put("name", "麗麗");
mapStr1.put("sex", "女");
mapStr1.put("age", 22);
mapStr1.put("tel", "110");
Map<String, Object> mapStr2 = new HashMap<String, Object>();
mapStr2.put("name", "麗麗");
mapStr2.put("sex", "女");
mapStr2.put("age", 23);
mapStr2.put("tel", "120");
Map<String, Object> mapStr3 = new HashMap<String, Object>();
mapStr3.put("name", "麗麗");
mapStr3.put("sex", "女");
mapStr3.put("age", 24);
mapStr3.put("tel", "110");
mapList.add(mapStr1);
mapList.add(mapStr2);

mapList.add(mapStr3);

ArrayList<Map<String, Object>> cs = mapList.stream()

.collect(Collectors

.collectingAndThen(Collectors

.toCollection(() -> new TreeSet<>(new Comparator<Map<String, Object>>() {

@Override    //重寫比較器
public int compare(Map<String, Object> o1, Map<String, Object> o2) {
if (o1.get("tel").equals(o2.get("tel"))) {
return 0;
}
return 1;
}

})), ArrayList::new));

               //迴圈取出結果

cs.forEach(m -> {
System.out.println("======map========");
m.keySet().forEach(n -> System.out.println(n + "-->" + m.get(n)));

});

應用場景（二）：

    對list<T>中物件T的指定屬性的去重，比如唯一ID，tel，獲取新的list:去除了重複出現的指定屬性值的物件T

示例：

    要求過濾掉電話相同的user

                User u1 = new User(1, "小米1", "001號", "女", 21, "110");
User u2 = new User(2, "小米2", "002號", "男", 11, "120");
User u3 = new User(3, "小米3", "003號", "女", 21, "119");
User u4 = new User(4, "小米4", "004號", "女", 34, "110");

List<User> persons = Arrays.asList(u1, u2, u3, u4);

List<User> unique = persons.stream()

                    .collect(Collectors

                    .collectingAndThen(Collectors

                    .toCollection(() -> new TreeSet<>(Comparator

                    .comparing(User::getTel))), ArrayList::new));

                //迴圈取出結果

unique.forEach(p -> System.out.println(p.toString()));