java 一个List根据某个字段进行去重

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.Set;
import java.util.TreeSet;

List<User> userList = userService.getList();  //获取原数据集合
//定义一个去重后的集合
List<User> list = new ArrayList<User>();
//去重
Set<User> set = new TreeSet<User>(new Comparator<User>(){
	@Override
    public int compare(User a, User b) {
        return a.getUserId().compareTo(b.getUserId());
    }
});
set.addAll(userList);
list = new ArrayList<User>(set);