List<TraineeVo> l= traineeDao.getTrainees();
            Collections.sort(l,new Comparator<TraineeVo>(){
                @Override
                public int compare(TraineeVo t1,TraineeVo t2){
                    return t1.getDates().compareTo(t2.getDates());
                }
            });



public class TraineeVo {
    private String name;
    private String unit;
    private String duty;
       
    private String dates;
}    

按照TraineeVo中的date属性排序（规则自定）；

Collects集合工具类中的sort方法自定义compare规则（重写compare方法）;