调用es restful api进行查询，为什么返回的json结果会把不可见字符转为\u开始的unicode字符串？能够通过配置避免这个问题吗

查询返回的json[{"_scroll_id":"DnF1ZXJ5VGhlbkZldGNoIAAAAAAAC","took":4,"timed_out":false,"_shards":{"total":32,"successful":32,"skipped":0,"failed":0},"hits":{"total":1,"max_score":5.9224715,"hits":[{"_index":"tcpapmssam201903","_type":"ms_sam_bas_tab","_id":"20190325153810msspc2000059","_score":5.9224715,"_source":{"msg_content":"Q\u0006$application/vnd.wap.mms-message@cak160rZT5j0@\u001717323187684/TYPE=PLMN@\u0004@@$V\u0005\u0003\u0003http://211.137.36.215:181/iNeG51@"}}]}}
不可见字符全部变为\u开始的unicode字符串，例如：\u0005，但是对于中文，可见字符没这个问题。查询结果的原始内容见附件图片。
想确认一下通过restful api返回的json，会把哪些字符转为\u开始的unicode字符串？
另通过java client不会有这个问题。