1、多属性合并

根据stream中对象的多个相同属性对不同的属性进行合并/聚合

//比如我们需要根据 相同的年龄 性别 ，把名字拼接起来（或者是别的操作）

List<User> list = new ArrayList();
User user1 = new User1();
user1.name = "张三";
user1.sex = "男"；
user1.age = 18;

User user2 = new User1();
user3.name = "李四";
user1.sex = "男"；
user3.age = 18;
list.add(user1); list.add(user2);

  Map<String, User> sexAndAge = list.stream().collect(Collectors.toMap(item ->                        
    item.getName +   "-" + item.getSex() ,  vo -> vo, (v1,v2)-> {
      v1.getname() + "-" + v2.getname();
    return v1;
}) );

2、根据多字段去重

        List<user> infoList = new ArrayList<>();
        //实体类   orderNumber  userName  age
        infoList.add(new user("1", "xc", "22"));
        infoList.add(new user("1", "xc", "33"));
        infoList.add(new user("2", "xc", "23"));
        infoList.add(new user("2", "xc", "33"));
        infoList.add(new user("2", "xy", "22"));
        List<user> list = infoList.stream()
                .collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(
                        Comparator.comparing(f -> f.getUserName()  + "-" +  f.getOrderNumber()))), ArrayList::new));
        System.out.println(list);

3、根据多字段获取重复数据

        List<user> infoList = new ArrayList<>();
        //实体类   orderNumber  userName  age
        infoList.add(new user("1", "xc", "22"));
        infoList.add(new user("1", "xc", "33"));
        infoList.add(new user("2", "xc", "23"));
        infoList.add(new user("2", "xc", "33"));
        infoList.add(new user("2", "xy", "22"));
        List<user> list = infoList.stream().
.collect(Collectors.groupingBy(person -> person.getUserName() + "_" + person.getOrderNumber()+ "_"))
.values().stream().filter(list -> list.size() >1).map(list -> list.get(0)).collect(Collectors.toList());        
        System.out.println(list);