Send HTTP GET and POST requests in Kotlin

This post will discuss how to send HTTP GET and POST request in Kotlin.

1. Using `URLConnection`

We can send HTTP request in Kotlin using the java.net.URLConnection class. The idea is to get an URLConnection object by invoking the openConnection() function on a URL. Then get an input stream by calling getInputStream() and create a BufferedReader on the input stream to read from it.

Following is a simple example demonstrating HTTP GET request.

import java.io.BufferedReader

import java.io.InputStreamReader

import java.net.URL

fun main() {

val url = URL("https://reqres.in/api/users?page=1")

val connection = url.openConnection()

BufferedReader(InputStreamReader(connection.getInputStream())).use { inp ->

var line: String?

while (inp.readLine().also { line = it } != null) {

println(line)

}

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Output:

Alternatively, to send an HTTP POST request, set URLConnection.setDoOutput() function to true and also write the POST parameters to the output stream of the connection. Here’s what the code would look like:

import java.io.BufferedReader

import java.io.DataOutputStream

import java.io.InputStreamReader

import java.net.URL

fun main() {

val url = URL("https://postman-echo.com/post")

val postData = "foo1=bar1&foo2=bar2"

val conn = url.openConnection()

conn.doOutput = true

conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded")

conn.setRequestProperty("Content-Length", postData.length.toString())

DataOutputStream(conn.getOutputStream()).use { it.writeBytes(postData) }

BufferedReader(InputStreamReader(conn.getInputStream())).use { bf ->

var line: String?

while (bf.readLine().also { line = it } != null) {

println(line)

}

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Output:

{"args":{},"data":"","files":{},"form":{"foo1":"bar1","foo2":"bar2"},"headers":{"x-forwarded-proto":"https","x-forwarded-port":"443","host":"postman-echo.com","x-amzn-trace-id":"Root=1-61c9d226-3a1f8340360c303e1da404e9","content-length":"19","content-type":"application/x-www-form-urlencoded","user-agent":"Java/13.0.1","accept":"text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2"},"json":{"foo1":"bar1","foo2":"bar2"},"url":"https://postman-echo.com/post"}

2. Using `HttpUrlConnection`

The java.net.HttpURLConnection class is the subclass of java.net.URLConnection, which offers several HTTP-specific features. To get a HttpURLConnection object, we can cast the URLConnection instance to HttpURLConnection. To send an HTTP POST request, we can pass "POST" string literal to the HttpURLConnection#setRequestMethod() function. This is preferable over setDoOutput() function of URLConnection class.

This is demonstrated below:

import java.io.BufferedReader

import java.io.DataOutputStream

import java.io.InputStreamReader

import java.net.HttpURLConnection

import java.net.URL

fun main() {

val url = URL("https://postman-echo.com/post")

val postData = "foo1=bar1&foo2=bar2"

val conn = url.openConnection() as HttpURLConnection

conn.requestMethod = "POST"

conn.doOutput = true

conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded")

conn.setRequestProperty("Content-Length", postData.length.toString())

conn.useCaches = false

DataOutputStream(conn.outputStream).use { it.writeBytes(postData) }

BufferedReader(InputStreamReader(conn.inputStream)).use { br ->

var line: String?

while (br.readLine().also { line = it } != null) {

println(line)

}

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Output:

{"args":{},"data":"","files":{},"form":{"foo1":"bar1","foo2":"bar2"},"headers":{"x-forwarded-proto":"https","x-forwarded-port":"443","host":"postman-echo.com","x-amzn-trace-id":"Root=1-61c9d1dd-0bbed6304b2ee8fc17628da2","content-length":"19","content-type":"application/x-www-form-urlencoded","cache-control":"no-cache","pragma":"no-cache","user-agent":"Java/13.0.1","accept":"text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2"},"json":{"foo1":"bar1","foo2":"bar2"},"url":"https://postman-echo.com/post"}

The following code example demonstrates HTTP GET request using java.net.HttpUrlConnection.

import java.io.BufferedReader

import java.io.InputStreamReader

import java.net.HttpURLConnection

import java.net.URL

fun main() {

val url = URL("https://reqres.in/api/users?page=1")

val conn = url.openConnection() as HttpURLConnection

conn.requestMethod = "GET"

BufferedReader(InputStreamReader(conn.inputStream)).use { br ->

var line: String?

while (br.readLine().also { line = it } != null) {

println(line)

}

Download

Output:

That’s all about sending HTTP GET and POST request in Kotlin.

Send HTTP GET and POST requests in Kotlin

1. Using URLConnection

2. Using HttpUrlConnection

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1. Using `URLConnection`

2. Using `HttpUrlConnection`