如果允许的话，您可以使用hashmap来存储查询结果
通过这种方式，您可以获得总字段的长度或执行map提供的其他操作。
下面是示例代码

public ResponseEntity<?> postData(some request) {

    Map<String, Object> data = someRepository.getDataByID(someId); 
    // data that you  get from sql query, note that you have to map it though 
    // in response type of sql query of whatever java tool you are using for getting the sql data
    System.out.println("The fields are: " + data.keySet()); 
    for(String fieldKey: data) {
         System.out.println("key is " + key);
         System.out.println("value is " + data.get(key));
    }
    ... your logic
    return new ResponseEntity(data, HttpStatus.OK);
}