各种遇到的异常以及异常的处理

1. java.lang.UnsupportedOperationException: A TupleBackedMap cannot be modified.

报错类似的代码：

List<HashMap<String, Object>> newMapList = new ArrayList<>();
for (int i = 0; i < mapList.size(); i++) {
          Map<String, Object> one = mapList.get(i);
         one.put("something",1);
        //我发现当我往这个one里面添加数据的时候就会报上面的错
}

解决方案：

List<HashMap<String, Object>> newMapList = new ArrayList<>();
for (int i = 0; i < mapList.size(); i++) {
      Map<String, Object> one = mapList.get(i);
      HashMap<String, Object> newOne = new HashMap<>();
      newOne.putAll(one);
      newOne.put("something",1);
        //重新定义一个新的map,把one放入到newOne里面就好了
}

2.java.lang.NullPointerException: null

下面这样如果是其它情况会返回一个null是不允许的

  @Override
    public List<String> moduleIdListByUserId(String userId) {
        List<String> projectIdList = getProjectIdList(userId);
        if (projectIdList.size()>0) {
           return  getModuleIdList(projectIdList);
        }
        return null;
    }

应该改为下面这样，首先new一个，即使没有值，也返回

  @Override
    public List<String> moduleIdListByUserId(String userId) {
        List<String> moduleIdList =new ArrayList<>();
        List<String> projectIdList = getProjectIdList(userId);
        if (projectIdList.size()>0) {
            moduleIdList= getModuleIdList(projectIdList);
        }
        return moduleIdList;
    }

3. mysql 把一个时间字段置NULL报错，但是结果不影响

[Err] 1055 - Expression #1 of ORDER BY clause is not in GROUP BY clause and contains nonaggregated column ‘information_schema.PROFILING.SEQ’ which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by