android - how to remove hidden junk character after php json encode

I was created JSON array fromjson_encode using PHP. I gave my array tojson_encode . It's created JSON array very well. And i feed this JSON array to my android apps. When i am gonna read this url at android it's return following EXCEPTION ERROR.

Error parsing data org.json.JSONException: Value  of type java.lang.String cannot be converted to JSONObject
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But when i am gonna create jason object at android adding this following line

jObj=new JSONObject(json.substring(json.indexOf("{"), json.lastIndexOf("}") + 1));
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It's working perfectly.

But i don't want to need the my second type solution. I need the php solution when i am put my json_encode on php.

And also at IOS the JSON return NULL values. How can i fix in both IOS and Android

Thanks advance