使用Collections.sort（）时，报java.lang.UnsupportedOperationException

川长思鸟来 2022-02-28 09:56 447阅读 0赞

from stackoverflow

[https://stackoverflow.com/questions/21854353/why-does-collections-sort-throw-unsupported-operation-exception-while-sorting-by][https_stackoverflow.com_questions_21854353_why-does-collections-sort-throw-unsupported-operation-exception-while-sorting-by]

private List<MaterialVo> sortByLimit(List<MaterialVo> voList ){
            if(CollectionUtils.isEmpty(voList)){
               return null;
            }
    //不明白为什么 这时我的voList变成了UNmodified状态，想要sort还要重新构造一下（如下）
            voList = new ArrayList<>(voList);//由于java.lang.UnsupportedOperationException，所以把list重新构造了一遍
            voList.sort((MaterialVo o1, MaterialVo o2) -> {
                if(null != o1 && null != o2){
                    String flag1 = o1.getFlag();
                    String flag2 = o2.getFlag();
                    if(!StringUtils.isEmpty(flag1) && !StringUtils.isEmpty(flag2)){
                        int i = Integer.parseInt(flag2) - Integer.parseInt(flag1);
                        if(i == 0){//flag相同的时候 按照更新时间排一下顺序
                            LocalDateTime updateTime1 = o1.getUpdateTime();
                            LocalDateTime updateTime2 = o2.getUpdateTime();
                            if(null != updateTime1 && null != updateTime2){
                                boolean after = updateTime1.isAfter(updateTime2);
                                //如果前者晚于后者创建，则把前者排在前边
                                if(after){
                                    return -1;
                                }else{
                                    return 1;
                                }
                            }
                        }else {
                            return i;
                        }
                    }
                }
                return 0;
            });
    
            return voList;
        }

[https_stackoverflow.com_questions_21854353_why-does-collections-sort-throw-unsupported-operation-exception-while-sorting-by]: https://stackoverflow.com/questions/21854353/why-does-collections-sort-throw-unsupported-operation-exception-while-sorting-by