可以尝试一下方法解决：
1、
httpPost.setHeader("Content-Type", "application/json; charset=UTF-8");
2、
httpPost.setEntity(new UrlEncodedFormEntity(nvps,"utf-8"));
3、如果还是不行，可以试下这种
httpPost.setHeader("Content-Type", "application/x-www-form-urlencoded; charset=UTF-8");
entity.setContentType(ContentType.APPLICATION_JSON);
参考：
https://chenzhihao.cc/archives/153
https://www.cnblogs.com/yixiu868/p/6637645.html
http://blog.csdn.net/anloan/article/details/50471337
HttpClient中文乱码问题排查
原文地址：https://www.cnblogs.com/EasonJim/p/8386225.html