getting a List back from a server using retrofit

I'm new to using Retrofit for networking in Android. So far I have successfully written code that sends a String to a PHP server. The server is configured to take my string, which contains a system ID and a password ("systemid=id&password=password"). It may seem odd to append parameters via a String like this but this is the way I have to do it for this project. Anyway, on the server if the id and password sent to it match certain criteria, it's sends back a list of file locations. So far, I am getting the proper response back from the server. In other words 'response.getMessage()' returns 'OK.' But how can I get the list that the server is trying to send back? Here is my implementation so far.

Interface:

public interface ExampleClient {

    @POST("login/fake_name.php")
    Call<String> sendStringToServer(@Body String string);

}

Here is my code within the Activity:

private void sendRequestToServer(String str) {
        Retrofit.Builder builder = new Retrofit.Builder()
                .baseUrl("http://www.example.com/")
                .addConverterFactory(GsonConverterFactory.create());

        Retrofit retrofit = builder.build();

        PromoterKiosksClient client = retrofit.create(ExampleClient.class);
        Call<List<String>> call = client.sendStringToServer(str);
        call.enqueue(new Callback<Void>() {
            @Override
            public void onResponse(Call<String> call, Response<String> response) {
                Log.d(TAG, response.toString());
                Log.d(TAG, response.message());

            }

            @Override
            public void onFailure(Call<String> call, Throwable t) {
                Toast.makeText(AdminActivity.this, "you suck! keep trying", Toast.LENGTH_SHORT).show();
            }
        });
    }

Is there somewhere in onResponse() that I can do this or do I need a totally different implementation? Thanks in advance

You are looking for response.body() ? Do you get a JSON response from the server? If so you can use POJO to convert your response. Would you be able to share your response here? You can use POJO to convert your result and name it Result.java and set that as your return type.

private void sendRequestToServer(String str) {
        Retrofit.Builder builder = new Retrofit.Builder()
                .baseUrl("http://www.example.com/")
                .addConverterFactory(GsonConverterFactory.create());

        Retrofit retrofit = builder.build();

        PromoterKiosksClient client = retrofit.create(ExampleClient.class);
        Call<Result> call = client.sendStringToServer(str);
        call.enqueue(new Callback<Void>() {
            @Override
            public void onResponse(Call<Result> call, Response<Result> response) {
                Log.d(TAG, response.toString());
                Log.d(TAG, response.message());
                response.body(); // have your all data


            }

            @Override
            public void onFailure(Call<Result> call, Throwable t) {
                Toast.makeText(AdminActivity.this, "you suck! keep trying", Toast.LENGTH_SHORT).show();
            }
        });
    }

Call<User> vs. Call<ResponseBody> vs. Call<Void>

Most endpoints will be declared with a specific return type, like Call. In this case Retrofit will always take the response body and try to convert it to Java objects. Of course, this takes time, memory and processing power.

If you can live without the mapped Java objects, you should choose Call. This makes the raw response payload available to you, but skips the mapping to Java objects. With this option, you still have the chance to analyze the payload (e.g., JSON).

The most efficient way is Call because it not only skips the conversion to Java objects, it also ignores the response body payload. When the response body is very large (e.g., a large JSON or an image), you can save a little bit of extra time and battery consumption by using Call. Of course, this results in the body() method of your response object returning null.

A good example to look at Consuming an API with retrofit and RXJava