List<User> userList = userList.stream()
        .collect(Collectors.collectingAndThen(Collectors.toCollection(
                () -> new TreeSet<>(Comparator.comparing(ReadData::getReadTime))), ArrayList::new));

示例：

	List<User> userList = new ArrayList<>();
    
    userList.add(new User("1","张三"));
    userList.add(new User("2","李四"));
    userList.add(new User("3","王五"));
    userList.add(new User("4","赵六");
    
    userList.add(new User("1","丁七");    //id相同，其他数据也相同
    userList.add(new User("3","许八"));  //id相同，其他数据不同
    
    System.out.println(userList);
    //根据userid去重
    userList = userList.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new  TreeSet<>(Comparator.comparing(User :: getUserId))), ArrayList::new));