Php 服务器端获取不到Android端发送的post数据！！！求解

Android  端 :

           private static String urlString = "http://192.168.10.20:8080/xampp/nfcdemo/readjson.php";

          private String jsonStr = "[{'USERID':'Peter','EAN':'1234567891234','PRURL':['http://localhost:8080','http://localhost:8080']}]";

         List<NameValuePair> entities = new ArrayList<NameValuePair>();

        entities.add(new BasicNameValuePair("json", jsonStr));

         HttpClient client = new DefaultHttpClient();

       

         HttpParams params = new BasicHttpParams();

         HttpConnectionParams.setConnectionTimeout(params,100000);

         HttpConnectionParams.setSoTimeout(params, 100000);

           

         HttpPost post = new HttpPost(urlString);

         post.setParams(params);

         post.setEntity(new UrlEncodedFormEntity(entities, "UTF-8"));

          

         HttpResponse resp = client.execute(post);

Php 服务器端:

          <?php

            $_POST['json']

        >

   取不到数据  求高手解决