java - Gson - attempting to convert json string to custom object -

here json returned server

{"errorcode":1005,"message":"username not exist"} 

here class error

public class errormodel { public int errorcode; public string message; } 

and here conversion code.

public static errormodel geterror(string json) {      gson gson = new gson();      try     {         errormodel err = gson.fromjson(json, errormodel.class);          return err;     }     catch(jsonsyntaxexception ex)     {         return null;     } } 

it throwing jsonsyntaxexception. ideas problem here?

edit: requested, here further elaboration.

my backend asp.net mvc 2 application acting rest api. backend isn't problem here, actions (and server errors) return json (using built in jsonresult). here's sample.

[httppost] public jsonresult authenticate(authenticaterequest request) {     var authresult = mobileservice.authenticate(request.username, request.password, request.adminpassword);      switch (authresult.result)     {          //logic omitted clarity          default:             return exceptionresult(errorcode.invalidcredentials, "invalid username/password");             break;     }      var user = authresult.user;      string token = sessionhelper.generatetoken(user.userid, user.username);      var result = new authenticateresult()     {         token = token     };      return json(result, jsonrequestbehavior.denyget); } 

the basic logic auth user cretentials , either return exceptionmodel json or authenticationresult json.

here server side exception model

public class exceptionmodel {     public int errorcode { get; set; }     public string message { get; set; }      public exceptionmodel() : this(null)     {      }      public exceptionmodel(exception exception)     {         errorcode = 500;         message = "an unknown error ocurred";          if (exception != null)         {             if (exception httpexception)                 errorcode = ((httpexception)exception).errorcode;              message = exception.message;         }     }      public exceptionmodel(int errorcode, string message)     {         errorcode = errorcode;         message = message;     } } 

when above authentication called invalid credentials, error result returned expected. json returned json above in question.

on android side, first build object key-value pairs.

public static hashmap<string, string> getauthenticationmodel(string username, string password, string adminpassword, string abbr) {     hashmap<string, string> request = new hashmap<string, string>();     request.put("siteabbreviation", abbr);     request.put("username", username);     request.put("password", password);     request.put("adminpassword", adminpassword);      return request; } 

then, send off http post , return string whatever sent back.

public static string post(serviceaction action, map<string, string> values) throws ioexception {     string serviceurl = getserviceurl(action);      url url = new url(serviceurl);      urlconnection connection = url.openconnection();     connection.setdoinput(true);     connection.setdooutput(true);     connection.setusecaches(false);     connection.setrequestproperty("content-type", "application/x-www-form-urlencoded");      string data = getpairsasstring(values);      dataoutputstream output = new dataoutputstream(connection.getoutputstream());     output.writebytes(data);     output.flush();     output.close();      datainputstream input = new datainputstream(connection.getinputstream());      string line;     string result = "";     while (null != ((line = input.readline())))     {         result += line;     }     input.close ();      return result; }  private static string getserviceurl(serviceaction action) {     return "http://192.168.1.5:33333" + action.tostring(); }  private static string getpairsasstring(map<string, string> values){      string result = "";     iterator<entry<string, string>> iter = values.entryset().iterator();      while(iter.hasnext()){         map.entry<string, string> pairs = (map.entry<string, string>)iter.next();          result += "&" + pairs.getkey() + "=" + pairs.getvalue();     }      //remove first &     return result.substring(1); } 

then take result , pass parser see if error

public static errormodel geterror(string json) {      gson gson = new gson();      try     {         errormodel err = gson.fromjson(json, errormodel.class);          return err;     }     catch(jsonsyntaxexception ex)     {         return null;     } } 

but, jsonsyntaxexception thrown.

might know more exception, same code sample works fine here. suspect there's piece of code omitted that's causing problem (perhaps creation/retrieval of json string). here's code sample worked fine me on java 1.6 , gson 1.6:

import com.google.gson.gson;  public class errormodel {   public int errorcode;   public string message;   public static void main(string[] args) {     string json = "{\"errorcode\":1005,\"message\":\"username not exist\"}";     gson gson = new gson();     errormodel err = gson.fromjson(json, errormodel.class);     system.out.println(err.errorcode);     system.out.println(err.message);   } }