JSON (JavaScript Object Notation) is a popular data format used for representing structured data. Kotlin is a modern programming language that is designed to interoperate with Java. In this article, we'll look at how to use Kotlin to work with JSON data.
We'll start by looking at the different ways to process JSON data in Kotlin. We'll then look at how to generate JSON data. We'll finish up by looking at some tips for working with JSON data in Kotlin.
There are a few different ways to process JSON data in Kotlin. We can use the standard library, we can use Kotlinx.Serialization, or we can use a third-party library like Gson.
The Kotlin standard library provides a set of functions for processing JSON data. These functions are located in the package kotlin.io.json.
To use the standard library, we need to add a dependency to our build.gradle file:
implementation 'org.jetbrains.kotlin:kotlin-stdlib-jdk8'
We can then use the json function to parse JSON data:
val jsonData = """
{
"name": "john",
"age": 30
}
""".trimIndent()
val data = json.parseJson(jsonData)
The data variable is now a JsonObject. We can access the data in the JsonObject using the get function:
val name = data.get("name") // "john"
val age = data.get("age") // 30
We can also use the getValue function to get the data as a specific type:
val name = data.getValue<String>("name") // "john"
val age = data.getValue<Int>("age") // 30
If we try to get a value that doesn't exist, we'll get a null value:
val address = data.getValue<String>("address") // null
To avoid this, we can use the optValue function. This function will return a default value if the requested value doesn't exist:
val address = data.optValue<String>("address") // ""
We can also use the jsonArray function to parse JSON arrays:
val jsonData = """
[
{
"name": "john",
"age": 30
},
{
"name": "jane",
"age": 20
}
]
""".trimIndent()
val data = json.parseJson(jsonData)
The data variable is now a JsonArray. We can use the get function to get the data in the JsonArray:
val firstPerson = data.get(0) // { "name": "john", "age": 30 }
val secondPerson = data.get(1) // { "name": "jane", "age": 20 }
We can also use the getValue function to get the data as a specific type:
val firstPerson = data.getValue<JsonObject>(0) // { "name": "john", "age": 30 }
val secondPerson = data.getValue<JsonObject>(1) // { "name": "jane", "age": 20 }
If we try to get a value that doesn't exist, we'll get a null value:
val thirdPerson = data.getValue<JsonObject>(2) // null
Kotlinx.Serialization is a library that provides support for serializing and deserializing JSON data. To use Kotlinx.Serialization, we need to add a dependency to our build.gradle file:
implementation 'org.jetbrains.kotlinx:kotlinx-serialization-runtime:0.12.0'
We can then use the @Serializable annotation to annotate our data classes:
@Serializable
data class Person(val name: String, val age: Int)
We can then use the Json class to serialize and deserialize our data classes:
val jsonData = """
{
"name": "john",
"age": 30
}
""".trimIndent()
val data = Json.decodeFromString<Person>(jsonData)
The data variable is now a Person object. We can access the data in the Person object using the properties that we defined in our data class:
val name = data.name // "john"
val age = data.age // 30
We can also use the Json class to serialize our data classes to JSON data:
val data = Person("john", 30)
val jsonData = Json.encodeToString(data)
The jsonData variable is now a JSON string that contains the data from our Person object.
Gson is a popular third-party library for working with JSON data. To use Gson, we need to add a dependency to our build.gradle file:
implementation 'com.google.code.gson:gson:2.8.6'
We can then use the fromJson function to deserialize JSON data:
val jsonData = """
{
"name": "john",
"age": 30
}
""".trimIndent()
val data = gson.fromJson(jsonData)
The data variable is now a JsonObject. We can access the data in the JsonObject using the get function:
val name = data.get("name") // "john"
val age = data.get("age") // 30
We can also use the getAsJsonObject function to get the data as a JsonObject:
val name = data.getAsJsonObject("name") // "john"
val age = data.getAsJsonObject("age") // 30
If we try to get a value that doesn't exist, we'll get a null value:
val address = data.getAsJsonObject("address") // null
To avoid this, we can use the optAsJsonObject function. This function will return a JsonObject with the null value if the requested value doesn't exist:
val address = data.optAsJsonObject("address") // {"address":null}
We can also use the fromJson function to deserialize JSON arrays:
val jsonData = """
[
{
"name": "john",
"age": 30
},
{
"name": "jane",
"age": 20
}
]
""".trimIndent()
val data = gson.fromJson(jsonData)
The data variable is now a JsonArray. We can use the get function to get the data in the JsonArray:
val firstPerson = data.get(0) // { "name": "john", "age": 30 }
val secondPerson = data.get(1) // { "name": "jane", "age": 20 }
We can also use the getAsJsonArray function to get the data as a JsonArray:
val firstPerson = data.getAsJsonArray(0) // { "name": "john", "age": 30 }
val secondPerson = data.getAsJsonArray(1) // { "name": "jane", "age": 20 }
If we try to get a value that doesn't exist, we'll get a null value:
val thirdPerson = data.getAsJsonArray(2) // null
To avoid this, we can use the optAsJsonArray function. This function will return a JsonArray with the null value if the requested value doesn't exist:
val thirdPerson = data.optAsJsonArray(2) // [null]
We can also use the toJson function to serialize our data classes to JSON data:
val data = Person("john", 30)
val jsonData = gson.toJson(data)
The jsonData variable is now a JSON string that contains the data from our Person object.
There are a few different ways to generate JSON data in Kotlin. We can use the standard library, we can use Kotlinx.Serialization, or we can use a third-party library like Gson.
The Kotlin standard library provides a set of functions for generating JSON data. These functions are located in the package kotlin.io.json.
To use the standard library, we need to add a dependency to our build.gradle file:
implementation 'org.jetbrains.kotlin:kotlin-stdlib-jdk8'
We can use the jsonObject function to create a JsonObject:
val data = jsonObject {
"name" to "john"
"age" to 30
}
We can then use the toString function to convert the JsonObject to a JSON string:
val jsonData = data.toString()
The jsonData variable is now a JSON string that contains the data from our JsonObject.
We can also use the jsonArray function to create a JsonArray:
val data = jsonArray {
+ jsonObject {
"name" to "john"
"age" to 30
}
+ jsonObject {
"name" to "jane"
"age" to 20
}
}
We can then use the toString function to convert the JsonArray to a JSON string:
val jsonData = data.toString()
The jsonData variable is now a JSON string that contains the data from our JsonArray.
Kotlinx.Serialization is a library that provides support for serializing and deserializing JSON data. To use Kotlinx.Serialization, we need to add a dependency to our build.gradle file:
implementation 'org.jetbrains.kotlinx:kotlinx-serialization-runtime:0.12.0'
We can then use the @Serializable annotation to annotate our data classes:
@Serializable
data class Person(val name: String, val age: Int)
We can then use the Json class to serialize and deserialize our data classes:
val data = Person("john", 30)
val jsonData = Json.encodeToString(data)
The jsonData variable is now a JSON string that contains the data from our Person object.
Gson is a popular third-party library for working with JSON data. To use Gson, we need to add a dependency to our build.gradle file:
implementation 'com.google.code.gson:gson:2.8.6'
We can then use the toJson function to serialize our data classes to JSON data:
val data = Person("john", 30)
val jsonData = gson.toJson(data)
The jsonData variable is now a JSON string that contains the data from our Person object.
Here are a few tips for working with JSON data in Kotlin:
jsonObject function to create a JsonObject.jsonArray function to create a JsonArray.get function to get the value of a key in a JsonObject.getValue function to get the value of a key in a JsonObject as a specific type.optValue function to get the value of a key in a JsonObject as a specific type with a default value.get function to get the value at an index in a JsonArray.getValue function to get the value at an index in a JsonArray as a specific type.toString function to convert a JsonObject or JsonArray to a JSON string.@Serializable annotation to annotate data classes.Json class to serialize and deserialize data classes.toJson function to serialize data classes to JSON data.In this article, we've looked at how to use Kotlin to work with JSON data. We've looked at the different ways to process JSON data and how to generate JSON data. We've also looked at some tips for working with JSON data in Kotlin.