How to handle nullable fields in JSON using GSON in Kotlin Android

How to handle nullable fields in JSON using GSON in Kotlin Android.

Here's a detailed step-by-step tutorial on how to handle nullable fields in JSON using GSON in Kotlin Android.

Step 1: Add GSON Dependency

First, you need to add the GSON library to your project. Open your app-level build.gradle file and add the following line to the dependencies block:

implementation 'com.google.code.gson:gson:2.8.7'

Then, sync your project to download the GSON library.

Step 2: Create a Data Class

Next, you need to create a data class that represents the structure of your JSON response. For example, let's say you have a JSON response containing a user's name, age, and address. Open your Kotlin file and define a data class like this:

data class User(
    val name: String?,
    val age: Int?,
    val address: String?
)

Note the use of nullable types (String? and Int?) for the fields. This allows these fields to have null values if they are not present in the JSON response.

Step 3: Deserialize JSON using GSON

To deserialize the JSON response into your data class, you can use GSON's fromJson method. Here's an example of how to do it:

val jsonString = "{ \"name\": \"John\", \"age\": 25 }" // Example JSON string
val gson = Gson()
val user = gson.fromJson(jsonString, User::class.java)

In the example above, we have a JSON string with only the name and age fields. The fromJson method takes the JSON string and the target data class as parameters and returns an instance of the data class.

Step 4: Handle Nullable Fields

Since the fields in the data class are nullable, you need to handle the case where they have null values in the JSON response. Here's how you can do it:

if (user.name != null) {
    // Name is present in the JSON response
    // Handle the non-null value
} else {
    // Name is not present in the JSON response
    // Handle the null value or provide a default value
}

Similarly, you can check for null values in other fields like age and address and handle them accordingly.

Step 5: Serialize Object to JSON

If you want to serialize an object of your data class back to JSON, you can use GSON's toJson method. Here's an example:

val user = User("John", 25, null) // Example User object
val gson = Gson()
val jsonString = gson.toJson(user)

In the example above, we have created a User object with a null address field. The toJson method converts the object to a JSON string.

That's it! You have learned how to handle nullable fields in JSON using GSON in Kotlin Android. Remember to handle null values appropriately when working with nullable fields in your data class.