应用场景（一）：
1.对list<map>中map中某个指定的key的value的去重，得到新的list：去除了重复出现指定key的value值得map
示例：
要求：过滤掉电话相同的map
List<Map<String, Object>> mapList = new ArrayList<Map<String, Object>>();
Map<String, Object> mapStr1 = new HashMap<String, Object>();
mapStr1.put(“name”, “丽丽”);
mapStr1.put(“sex”, “女”);
mapStr1.put(“age”, 22);
mapStr1.put(“tel”, “110”);
Map<String, Object> mapStr2 = new HashMap<String, Object>();
mapStr2.put(“name”, “丽丽”);
mapStr2.put(“sex”, “女”);
mapStr2.put(“age”, 23);
mapStr2.put(“tel”, “120”);
Map<String, Object> mapStr3 = new HashMap<String, Object>();
mapStr3.put(“name”, “丽丽”);
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 //重写比较器
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));
//循环取出结果
cs.forEach(m -> {
System.out.println(“======map========”);
m.keySet().forEach(n -> System.out.println(n + “–>” + m.get(n)));
});
应用场景（二）：
对list<T>中对象T的指定属性的去重，比如唯一ID，tel，获取新的list:去除了重复出现的指定属性值的对象T
示例：
要求过滤掉电话相同的user
User u1 = new User(1, “小米1”, “001号”, “女”, 21, “110”);
User u2 = new User(2, “小米2”, “002号”, “男”, 11, “120”);
User u3 = new User(3, “小米3”, “003号”, “女”, 21, “119”);
User u4 = new User(4, “小米4”, “004号”, “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));
//循环取出结果
unique.forEach(p -> System.out.println(p.toString()));
