java - Need Help Connecting to Google App Engine With Retrofit -

i have followed google tutorial here, using android studio servlets module connect google app engine. able see toast message on device, meaning connected server , received response.

i noticed module uses asynctask handle background tasks. understand, retrofit simpler , effective method of handling tasks in background thread. trying replicate google tutorial mentioned above using retrofit 1.9.0 instead of servletpostasynctask java class provide.

below code:

mainactivity:

public class mainactivity extends appcompatactivity {  //set url of server, defined in google servlets module documentation private static string project_url = "http://retrofit-test-1203.appspot.com/hello";  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);     toolbar toolbar = (toolbar) findviewbyid(r.id.toolbar);     setsupportactionbar(toolbar);      //instantiate new restadapter object, setting endpoint url of server     restadapter restadapter = new restadapter.builder()             .setendpoint(project_url)             .build();      //instantiate new userservice object, , call "testrequst" method, created in interface     //to interact server     userservice userservice = restadapter.create(userservice.class);     userservice.testrequest("test_name", new callback<string>() {         @override         public void success(string s, response response) {             toast.maketext(getapplicationcontext(), response.tostring(), toast.length_long).show();          }          @override         public void failure(retrofiterror error) {             toast.maketext(getapplicationcontext(), error.getmessage(), toast.length_long).show();         }     });    } } 

userservice interface, required retrofit:

public interface userservice {  static string project_url = "http://retrofit-test-1203.appspot.com/hello";  @post(project_url) void testrequest(@query("test") string test, callback<string> cb);   } 

my servlet, required google servlets module:

public class myservlet extends httpservlet { @override public void doget(httpservletrequest req, httpservletresponse resp)         throws ioexception {     resp.setcontenttype("text/plain");     resp.getwriter().println("please use form post url"); }  @override public void dopost(httpservletrequest req, httpservletresponse resp)         throws ioexception {     string name = req.getparameter("name");     resp.setcontenttype("text/plain");     if(name == null) {         resp.getwriter().println("please enter name");     }     resp.getwriter().println("hello " + name);   } } 

in userservice.testrequest()method, pass in "test_name" string parameter. text hope pass server, , see toast displays "hello test_name" (after receiving server response), google app engine servlets module explains.

right now, receiving below error:

any advice on using retrofit google app engine appreciated, there limited documentation.

first of all, base url should domain of site i.e http://retrofit-test-1203.appspot.com (it should not include path resource you're trying access) declare this:

private static string project_url = "http://retrofit-test-1203.appspot.com" 

second, don't use base url(project_url in case) relative url in declaration of userservice interface. should use relative url here i.e "/hello" (and must start slash), this:

public interface userservice {     @post("/hello")    void testrequest(@query("test") string test, callback<string> cb);      }