需要帮助进行翻新连接到Google App Engine

Question

I have successfully followed the Google tutorial here , using the Android Studio Servlets module to connect to Google App Engine. I was able to see the Toast message on my device, meaning I successfully connected to the server and received a response.

I noticed that this module uses AsyncTask to handle the background tasks. From what I understand, Retrofit is a much simpler and effective method of handling tasks in the background thread. I am basically trying to replicate the Google Tutorial mentioned above using Retrofit 1.9.0 instead of the ServletPostAsyncTask Java class that they provide.

Below is my code:

MainActivity:

public class MainActivity extends AppCompatActivity {

//set the URL of the server, as defined in the 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 a new RestAdapter Object, setting the endpoint as the URL of the server
    RestAdapter restAdapter = new RestAdapter.Builder()
            .setEndpoint(PROJECT_URL)
            .build();

    //Instantiate a new UserService object, and call the "testRequst" method, created in the interface
    //to interact with the 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 by 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, as required by the 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 the form to POST to this 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 a name");
    }
    resp.getWriter().println("Hello " + name);
  }
}

In my userService.testRequest()method, I pass in "Test_Name" as the string parameter. This text is what I hope to pass to the server, and then see a toast that displays "Hello Test_Name" (after receiving a server response), just like the Google App Engine Servlets module explains.

Right now, I am receiving the below error:

Any advice on using Retrofit with Google App Engine is appreciated, as there is limited documentation.

Answer 1

First of all, your base url should just be the domain of the site ie http://retrofit-test-1203.appspot.com (it should not include the path to the resource you're trying to access) So declare it like this:

private static String PROJECT_URL = "http://retrofit-test-1203.appspot.com"

Second, don't use the base url(PROJECT_URL in this case) as the relative URL in the declaration of the UserService interface. You should only use the relative URL here ie "/hello" (and it must start with a slash), like this:

public interface UserService {

   @POST("/hello")
   void testRequest(@Query("test") String test, Callback<String> cb);


   }