How to parse JSON in Android using Kotlin

Last updated on: February 1, 2022

We’re going to parse JSON without using any 3rd party library but using the java class JSONTokener.

With the JSONTokener, we can parse a JSON string into an object. These objects can be cast as JSONObject or as JSONArray. In that way, we’ll be able to read the JSON values.

I’ll cover 3 cases that may you face when you’re trying to parse JSON:

• Simple JSON: Just a simple JSON without any complex structure
• Array JSON: The JSON structure begins with an array and without a key
• Nested JSON: Includes nested objects

Simple JSON

A simple JSON doesn’t have any complex structure, like arrays, nested objects, e.t.c, and it looks like that:

{
    "id": "1",
    "employee_name": "Jack Full",
    "employee_salary": "300800",
    "employee_age": "61"
}Code language: Swift (swift)

After getting the response from the HTTP request, you parse the JSON string into JSONObject, to get the JSON values:

val jsonObject = JSONTokener(response).nextValue() as JSONObject

// ID
val id = jsonObject.getString("id")
Log.i("ID: ", id)

// Employee Name
val employeeName = jsonObject.getString("employee_name")
Log.i("Employee Name: ", employeeName)

// Employee Salary
val employeeSalary = jsonObject.getString("employee_salary")
Log.i("Employee Salary: ", employeeSalary)

// Employee Age
val employeeAge = jsonObject.getString("employee_age")
Log.i("Employee Age: ", employeeAge)Code language: Kotlin (kotlin)

Array JSON

Sometimes, you might see a JSON start with an array and without having a key:

[
    {
        "id": "1",
        "employee_name": "Tiger Nixon",
        "employee_salary": "320800",
        "employee_age": "61"
    },
    {
        "id": "2",
        "employee_name": "Garrett Winters",
        "employee_salary": "170750",
        "employee_age": "63"
    },
    // ...
]Code language: Swift (swift)

After getting the response, you parse the JSON string into a JSONArray, and you’re looping through the array to get the JSON values.

val jsonArray = JSONTokener(response).nextValue() as JSONArray
for (i in 0 until jsonArray.length()) {
    // ID
    val id = jsonArray.getJSONObject(i).getString("id")
    Log.i("ID: ", id)

    // Employee Name
    val employeeName = jsonArray.getJSONObject(i).getString("employee_name")
    Log.i("Employee Name: ", employeeName)

    // Employee Salary
    val employeeSalary = jsonArray.getJSONObject(i).getString("employee_salary")
    Log.i("Employee Salary: ", employeeSalary)

    // Employee Age
    val employeeAge = jsonArray.getJSONObject(i).getString("employee_age")
    Log.i("Employee Age: ", employeeAge)

    // Save data using your Model

    // Notify the adapter
}

// Pass adapter to the RecyclerView adapterCode language: Kotlin (kotlin)

Tip: If a key does not exist in some objects, you can set it as optional like this:
val id = jsonArray.getJSONObject(i).optString(“id”)

Nested JSON

When a JSON object is inside another JSON object, it’s called ‘nested’ and will look like the following JSON structure:

{
    "data": [
        {
            "id": "1",
            "employee": {
                "name": "Tiger Nixon",
                "salary": {
                    "usd": 320800,
                    "eur": 273545
                },
                "age": "61"
            }
        },
        {
            "id": "2",
            "employee": {
                "name": "Garrett Winters",
                "salary": {
                    "usd": 170750,
                    "eur": 145598
                },
                "age": "63"
            }
        },
        // ...
    ]
}Code language: Swift (swift)

After getting the response, you parse the JSON string into a JSONObject. Then you get the “data” as a JSONArray and loop it through the array.

val jsonObject = JSONTokener(response).nextValue() as JSONObject

val jsonArray = jsonObject.getJSONArray("data")

for (i in 0 until jsonArray.length()) {

    // ID
    val id = jsonArray.getJSONObject(i).getString("id")
    Log.i("ID: ", id)

    // Employee
    val employee = jsonArray.getJSONObject(i).getJSONObject("employee")

    // Employee Name
    val employeeName = employee.getString("name")
    Log.i("Employee Name: ", employeeName)

    // Employee Salary
    val employeeSalary = employee.getJSONObject("salary")

    // Employee Salary in USD
    val employeeSalaryUSD = employeeSalary.getInt("usd")
    Log.i("Employee Salary in USD: ", employeeSalaryUSD.toString())

    // Employee Salary in EUR
    val employeeSalaryEUR = employeeSalary.getInt("eur")
    Log.i("Employee Salary: ", employeeSalaryEUR.toString())

    // Employee Age
    val employeeAge = employee.getString("age")
    Log.i("Employee Age: ", employeeAge)

    // Save data using your Model

    // Notify the adapter
}

// Pass adapter to the RecyclerView adapterCode language: Kotlin (kotlin)

You can find the final project here

If you have any questions, please feel free to leave a comment below