Retrofit 2 — Receive Plain-String Responses

Android apps usually interact with REST APIs, which often use JSON as a data format. We've focused almost all of our tutorials on sending JSON or XML requests, and converting JSON or XML responses. We briefly explored other data formats in our introduction to converters tutorial, but didn't go into more detail.

Learn how to receive and process plain-string responses from your API in this tutorial.

Retrofit Series Overview

  1. Callbacks (Coming soon)
  2. Annotations (Coming soon)
  3. Fluent Interface with Builders (Coming soon)

Scalars Converter for Plain Strings

To receive plain-text or plain-string responses you can utilize the scalars converter. You can integrate the converter by adding it as a dependency to your app's build.gradle:

dependencies {  
    // Retrofit
    compile 'com.squareup.retrofit2:retrofit:2.3.0'

    // Retrofit Scalars Converter
    compile 'com.squareup.retrofit2:converter-scalars:2.3.0'
}

Next, you need to describe the endpoint you want to interact with. In this demo case, you'll use a GET request with the dynamic URL feature to pass any URL to the method, and set the response type as String.

@GET()
Call<String> getStringResponse(@Url String url);  

You've finished the preparations. Next, you can use Retrofit to execute requests with the scalars converter and the created endpoint. You'll create a Retrofit object with the Retrofit builder and configure it to use the scalars converter:

Retrofit retrofit = new Retrofit.Builder()  
        .addConverterFactory(ScalarsConverterFactory.create())
        .baseUrl("https://your.base.url/")
        .build();

The final step is to use the Retrofit object to execute a request:

ScalarService scalarService = retrofit.create(ScalarService.class);  
Call<String> stringCall = scalarService.getStringResponse("https://futurestud.io");  
stringCall.enqueue(new Callback<String>() {  
    @Override
    public void onResponse(Call<String> call, Response<String> response) {
        if (response.isSuccessful()) {
            String responseString = response.body();
            // todo: do something with the response string
        }

    }

    @Override
    public void onFailure(Call<String> call, Throwable t) {

    }
});

In the code snippet above, you're executing a GET request for our homepage futurestud.io. Consequently, you'll receive a long string back (which is actually the website's HTML source). You can also use the above approach to receive plain strings from your API.

Summary

In this tutorial you've learned how you can set up Retrofit to access plain-string responses from requests. This could be a regular API call, where the server returns a string. But this could also be the HTML source of a website.

In the next tutorial we'll explore how you can crawl website sources with this method. You'll implement a Retrofit converter, which automatically maps from the HTML of a Wikipedia page to a useful Java object. Stay tuned!

Do you have further questions on this topic or about Retrofit in general? Let us know on Twitter @futurestud_io or leave a comment below.

Enjoy coding & make it rock!

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