Ktor HttpClient vs Retrofit: Missing JSON fields, fields that can be string or numeric, defaults and nulls

If you watch my YouTube channel, then you already know that I like to experiment and play with different technologies. In this video, I explore the different JSON responses that come back from Ktor's HttpClient vs Retrofit. I'll also go over missing JSON fields, JSON fields that can come back as a string or a numeric value, and how to handle nulls and defaults in our data classes.

For this app, I'm using the Open Food Facts API. Their GitHub Repo has a ton of info if you'd like to learn more.

First, let's take a look at the JSON data that I'm working with. Here's a typical "good" response that gets the nutrition data for cashews:

Make note of the field "carbohydrates_serving": 9

{
    "code": "0029000016071",
    "product": {
        "brands": "Planters",
        "nutriments": {
            "carbohydrates": 32.14,
            "carbohydrates_100g": 32.14,
            "carbohydrates_serving": 9,
            "carbohydrates_unit": "g",
            "carbohydrates_value": 32.14
        }
    },
    "status": 1,
    "status_verbose": "product found"
}

Now, here's the response from a different product. For this one, there is no "carbohydrates_serving": 9 field (at least in Postman and in the browser - more on this later).

{
    "code": "0078742366951",
    "product": {
        "brands": "Great Value",
        "nutriments": {
            "carbohydrates": 33.333333333333,
            "carbohydrates_100g": 33.333333333333,
            "carbohydrates_unit": "g",
            "carbohydrates_value": 33.333333333333
        }
    },
    "status": 1,
    "status_verbose": "product found"
}

The response using HttpClient is the same for both products, but in Retrofit, I get this string response - this is without serializing the body to a data class:

{"code":"0078742366951","product":{"brands":"Great Value",
  "nutriments":{"carbohydrates":33.333333333333,"carbohydrates_100g":33.333333333333,
    "carbohydrates_serving":"","carbohydrates_unit":"g","carbohydrates_value":33.333333333333
    }},"status":1,"status_verbose":"product found"}

Here, "carbohydrates_serving":"" is an empty string! 😵‍💫🤪🤔 Now we have 3 scenarios:

Carbs per serving returns a number, like 9, or 26
or, it's completely missing from the JSON response
and finally, it could be set to an empty string

So how do we handle this in our apps? The answer for me was different based on my API client. I prefer using Ktor's HttpClient in my projects, but for my latest one, I switched back to Retrofit just to get some variety in my life. So here's what I ran into while building my latest app, and I'll take you along on the journey.

First, I'll go over a Ktor HttpClient setup, then, I'll go over Retrofit. Here are the corresponding branches if you want to follow along:

https://github.com/santansarah/retrofit-vs-httpclient-null-json/tree/ktor_httpclient https://github.com/santansarah/retrofit-vs-httpclient-null-json/tree/retrofit

santansarah / retrofit-vs-httpclient-null-json

Ktor HttpClient vs Retrofit: Missing JSON fields, fields that can be string or numeric, defaults and nulls

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