Cannot cast response body to Custom class with Void as response type

[arushijain45]

I am using retrofit2, my use case calls an api which can either return with a response class (say User) or with null. So I am using Void response type. My onReponse() is shown below:

public void onResponse(Call<Void> call, Response<Void> response) {
    if (response.isSuccessful()) {
        if(response.raw().body() != null){
            //returns user response
            User user = (User) response.raw().body().source();
        }
        else{
            //returns null response
        }
    }
}

But I am getting IllegalStateException. Is it something wrong with the code.

[JakeWharton]

Using Void tells Retrofit to discard the response body entirely. If the API returns a User or the JSON literal null then just declaring the response type as User should work.

[arushijain45]

But when I was declaring User as Response Type, I was getting onResponse() callback when api returns user but when api returns null I am getting onFailure() callback (where I could not find the reason of failure which might be deserialising issue).

[JakeWharton]

In that case the failure exception indicates the problem that needs corrected. Please include its entire stacktrace.

[arushijain45]

Here is the stack trace:

java.io.EOFException: End of input at line 1 column 1 path $
08-09 12:24:55.540 25080-25080/com.x.y I/System.out:     at com.google.gson.stream.JsonReader.nextNonWhitespace(JsonReader.java:1393)
08-09 12:24:55.540 25080-25080/com.x.y I/System.out:     at com.google.gson.stream.JsonReader.doPeek(JsonReader.java:549)
08-09 12:24:55.541 25080-25080/com.x.y I/System.out:     at com.google.gson.stream.JsonReader.peek(JsonReader.java:425)
08-09 12:24:55.541 25080-25080/com.x.y I/System.out:     at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:205)
08-09 12:24:55.542 25080-25080/com.x.y I/System.out:     at retrofit2.converter.gson.GsonResponseBodyConverter.convert(GsonResponseBodyConverter.java:37)
08-09 12:24:55.543 25080-25080/com.x.y I/System.out:     at retrofit2.converter.gson.GsonResponseBodyConverter.convert(GsonResponseBodyConverter.java:25)
08-09 12:24:55.543 25080-25080/com.x.y I/System.out:     at retrofit2.ServiceMethod.toResponse(ServiceMethod.java:117)
08-09 12:24:55.543 25080-25080/com.x.y I/System.out:     at retrofit2.OkHttpCall.parseResponse(OkHttpCall.java:211)
08-09 12:24:55.543 25080-25080/com.x.y I/System.out:     at retrofit2.OkHttpCall$1.onResponse(OkHttpCall.java:106)
08-09 12:24:55.543 25080-25080/com.x.y I/System.out:     at okhttp3.RealCall$AsyncCall.execute(RealCall.java:133)
08-09 12:24:55.543 25080-25080/com.x.y I/System.out:     at okhttp3.internal.NamedRunnable.run(NamedRunnable.java:32)
08-09 12:24:55.543 25080-25080/com.x.y I/System.out:     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
08-09 12:24:55.543 25080-25080/com.x.y I/System.out:     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
08-09 12:24:55.544 25080-25080/com.x.y I/System.out:     at java.lang.Thread.run(Thread.java:838)

[JakeWharton]

Looks like your server returns a 0-byte body in that case. You can use a custom converter that returns null in this case such as #1554 (comment). Make sure you add it before the Gson converter in your Retrofit.Builder.

[arushijain45]

In my case responseBody.contentLength() is giving me -1 though responseBody.string() is correct (as sent from api). On adding this converter my service ends with onFailure() callback.