fastjson解析null值问题: 解决 null的属性不显示问题

null对应的key被过滤掉；这明显不是我们想要的结果，这时我们就需要用到fastjson的SerializerFeature序列化属性:

也就是这个方法：

JSONObject.toJSONString(Object object, SerializerFeature... features)

SerializerFeature有用的一些枚举值

QuoteFieldNames———-输出key时是否使用双引号,默认为true 
WriteMapNullValue——–是否输出值为null的字段,默认为false 
WriteNullNumberAsZero—-数值字段如果为null,输出为0,而非null 
WriteNullListAsEmpty—–List字段如果为null,输出为[],而非null 
WriteNullStringAsEmpty—字符类型字段如果为null,输出为”“,而非null 
WriteNullBooleanAsFalse–Boolean字段如果为null,输出为false,而非null

现在加上

Map < String , Object > jsonMap = new HashMap< String , Object>();  
jsonMap.put("a",1);  
jsonMap.put("b","");  
jsonMap.put("c",null);  
jsonMap.put("d","wuzhuti.cn");  
  
String str = JSONObject.toJSONString(jsonMap,SerializerFeature.WriteMapNullValue);  
System.out.println(str);  
//输出结果:{"a":1,"b":"","c":null,"d":"wuzhuti.cn"}  

一个代码实例:

private static final TypeReference<Map<String, Object>> MAP_TYPE_REFERENCE = new TypeReference<Map<String, Object>>() {
};

/**
 * @param tenantId
 * @param sql
 * @param timeout
 * @return
 * @throws SQLException
 */
@Override
public List<Map<String, Object>> queryWithJsonFormat(Long tenantId, String sql, long timeout) throws SQLException {
    // 获取驱动信息
    Map<Long, ConnectInfo> connectInfoMap = getDriverInfo().getConnectInfoMap();
    String clusterName = connectInfoMap.get(tenantId).getClusterName();

    String response = HttpClientUtils.postTextRequest(baseURL(clusterName), buildSQLWithTimeoutAndFormatJson(sql, timeout));
    if (response == null || response.isEmpty()) {
        return Collections.emptyList();
    }

    JSONArray dataArray = (JSONArray) JSON.parseObject(response).get("data");
    return dataArray.stream()
            .map(it ->
                    JSON.parseObject(JSON.toJSONString(it, SerializerFeature.WriteMapNullValue), MAP_TYPE_REFERENCE)
            )
            .collect(Collectors.toList());
}

其中,  response 返回值的数据结构:

{
  "meta": [
    {
      "name": "uid_basic_profile_edu_degree",
      "type": "Nullable(String)"
    },
    {
      "name": "count_uid_basic_profile_edu_degree",
      "type": "UInt64"
    }
  ],
  "data": [
    {
      "uid_basic_profile_edu_degree": "college",
      "count_uid_basic_profile_edu_degree": 533389
    },
    {
      "uid_basic_profile_edu_degree": null,
      "count_uid_basic_profile_edu_degree": 0
    },
    {
      "uid_basic_profile_edu_degree": "undergraduate",
      "count_uid_basic_profile_edu_degree": 2518436
    },
    {
      "uid_basic_profile_edu_degree": "master",
      "count_uid_basic_profile_edu_degree": 271653
    },
    {
      "uid_basic_profile_edu_degree": "high",
      "count_uid_basic_profile_edu_degree": 5585609
    }
  ],
  "rows": 5,
  "statistics": {
    "elapsed": 0.703029803,
    "rows_read": 1287687385,
    "bytes_read": 76340471397
  }
}