调用API时JSON序列化失败：Object is null问题求助

调用数据库保存接口时，updated at、updated by等字段为空，结果返回至Controller时触发错误：Could not write JSON: Object is null，根因异常为net.sf.json.JSONException: Object is null。

完整错误栈 #

com.fasterxml.jackson.databind.JsonMappingException: Object is null (through reference chain: java.util.HashMap["details"]->net.sf.json.JSONObject["template"]->net.sf.json.JSONObject["createTemplate"]->net.sf.json.JSONObject["attributes"]->net.sf.json.JSONArray[0]->net.sf.json.JSONObject["components"]->net.sf.json.JSONArray[1]->net.sf.json.JSONObject["example"]->net.sf.json.JSONNull["empty"])

相关Controller代码 #

@PostMapping(value = "/saving",produces = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<Map<String, Object>> save(
    @RequestHeader(value = "apps") String apps,
    @RequestHeader(value = "module") String module,
    @Valid @RequestBody CreateTemplate requestData) throws IOException, InterruptedException, URISyntaxException, ApiResponseThrow 
{
    
    log.info("START saveTemplateQontak function");
    Map<String, Object> result = new HashMap<>();
    
    String jwt = AuthTokenFilter.parseJwt(request);
    String username = jwtUtils.getUserNameFromJwtToken(jwt);

    LogFormat logFormat = new LogFormat();
    logFormat.setAction("saving");
    logFormat.setApps(apps);
    logFormat.setModule(module);
    logFormat.setUser(username);
    log.info("DATA BEFORE == {}", objectMapper.writeValueAsString(requestData));
    log.info("log-format == {}", logFormat);
    
    // JSONObject token = qontakService.getTokenQontak();
    // JSONObject res = qontakService.saveTemplateToQontak(objectMapper.writeValueAsString(requestData), token.get("access_token").toString());
    // requestData.getAttributes().get(0).getComponents().get(0).getType()
    JSONObject res = templateService.saveHeaderTemplate(requestData, logFormat);
    log.info("END templateService.save() CREATE");

    result.put("httpCode", HttpStatus.OK);
    result.put("status", "00");
    result.put("message", "Success Saving");
    result.put("details",res);

    log.info("END save function");

    return new ResponseEntity<Map<String, Object>>(result, HttpStatus.OK);
}

解决方案 #

1. 配置Jackson忽略null字段 #

Spring默认使用Jackson序列化JSON，可全局配置忽略null值，避免因null字段触发异常：

• 通过application.yml配置：

spring:
  jackson:
    default-property-inclusion: non_null

• 或者通过配置类自定义ObjectMapper：

@Configuration
public class JacksonConfig {
    @Bean
    public ObjectMapper objectMapper() {
        ObjectMapper objectMapper = new ObjectMapper();
        // 序列化时忽略null字段
        objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
        return objectMapper;
    }
}

2. 修复Service层返回的JSONObject #

错误栈显示example字段对应net.sf.json.JSONNull，导致Jackson无法正常序列化。在Service层构建JSONObject时，过滤掉null值或替换JSONNull：

// 示例：构建components的JSONObject时处理null值
if (component.getExample() == null) {
    jsonObject.remove("example"); // 移除null字段
} else {
    jsonObject.put("example", component.getExample());
}

3. 统一JSON处理库，避免混用 #

当前代码混用了net.sf.json和Jackson，两者兼容性不佳。建议统一使用Jackson的ObjectNode替代net.sf.json.JSONObject，或者将现有JSONObject转为Jackson可处理的结构：

// 将net.sf.json.JSONObject转为Jackson的ObjectNode
ObjectMapper mapper = new ObjectMapper();
ObjectNode jacksonNode = mapper.readValue(res.toString(), ObjectNode.class);
result.put("details", jacksonNode);

内容的提问来源于stack exchange，提问作者Adam Abdullah