public static List<String> extractFields(List<JSONObject> jsonObjects, String fieldName) {

        List<String> result = new ArrayList<String>();
        if (CommonUtils.isEmpty(jsonObjects)) {
            return result;
        } else {
            for (JSONObject jsonObject : jsonObjects) {
                result.add(extractField(jsonObject, fieldName));
            }
        }

        return result;
    }
for json convert

@param contents
@return
test/test-integration/src/test/java/com/alipay/sofa/rpc/server/tracer/util/TracerChecker.java