Write JSON to a file in Kotlin

This post will discuss how to write JSON data to a file in Kotlin.

1. Using `PrintWriter`

The idea is to create a PrintWriter instance and call its write() function to write the JSON string. To write to a file, construct a FileWriter using the platform’s default character encoding.

The following solution demonstrates this using the JSON for Java library. It creates a file with the JSON string {"offices":["California","Washington","Virginia"],"name":"Microsoft","employees":182268}. The JSON file will be created if the file does not exist, otherwise, the existing file will be truncated.

import org.json.JSONException

import org.json.JSONObject

import java.io.FileWriter

import java.io.PrintWriter

import java.nio.charset.Charset

fun main() {

val path = "/json/microsoft.json"

val json = JSONObject()

try {

json.put("name", "Microsoft")

json.put("employees", 182268)

json.put("offices", listOf("California", "Washington", "Virginia"))

} catch (e: JSONException) {

e.printStackTrace()

}

try {

PrintWriter(FileWriter(path, Charset.defaultCharset()))

.use { it.write(json.toString()) }

} catch (e: Exception) {

e.printStackTrace()

}

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We can also use the Gson library to convert an object to a JSON string using its toJson() function, as shown below:

import com.google.gson.Gson

import java.io.FileWriter

import java.io.PrintWriter

class Company(

var name: String,

var employees: Int,

var offices: List<String>

)

fun main() {

val companies = Company(

"Microsoft", 182268, listOf("California", "Washington", "Virginia")

)

val path = "/json/microsoft.json"

try {

PrintWriter(FileWriter(path)).use {

val gson = Gson()

val jsonString = gson.toJson(companies)

it.write(jsonString)

}

} catch (e: Exception) {

e.printStackTrace()

}

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2. Using Jackson library

Jackson library already provides the ObjectMapper#writeValue() function to serialize Kotlin objects as a JSON string and write it to a file. A typical invocation for this function would look like below:

import org.codehaus.jackson.map.ObjectMapper

import java.io.File

import java.io.IOException

class Company(

var name: String,

var employees: Int,

var offices: List<String>

)

fun main() {

val companies = Company(

"Microsoft", 182268, listOf("California", "Washington", "Virginia")

)

val path = "/json/microsoft.json"

try {

val mapper = ObjectMapper()

mapper.writeValue(File(path), companies)

} catch (e: IOException) {

e.printStackTrace()

}

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That’s all about writing JSON data to a file in Kotlin.

Write JSON to a file in Kotlin

1. Using PrintWriter

2. Using Jackson library

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1. Using `PrintWriter`