POST

Learn POST requests with client.post.

POST request

A POST request sends new data to the server. In Ktor you make it with client.post(url); the body is added with setBody.

Example: client.post("https://api.example.com/users") { setBody(newUser) }. Here newUser is a Kotlin object; the ContentNegotiation plugin turns it into JSON. POST creates a new resource; PUT updates an existing one. The response is again an HttpResponse. To set the body type use contentType(ContentType.Application.Json).

Exercise Make a POST request and print

Create an HttpClient. Make a POST request with val response = client.post("https://api.example.com/users"). Print println("Sent"). Then close with client.close().

Show example solution

fun main() {
    val client = HttpClient()
    val response = client.post("https://api.example.com/users")
    println("Sent")
    client.close()
}

Body and Content-Type

To send a body in a POST request use setBody(data). To declare the body type add contentType(ContentType.Application.Json).

If the ContentNegotiation plugin is installed, the Kotlin object is serialized to JSON automatically. Example: client.post(url) { contentType(ContentType.Application.Json); setBody(user) }. The body is UTF-8 encoded; special characters are escaped. The response body is read again with response.body<T>(). Picking the right Content-Type helps the server recognize the body.

Test yourself

What is the main difference between POST and PUT?
- POST reads, PUT writes
- POST is faster
- PUT only deletes
- POST creates a new resource, PUT updates
Show answer

POST creates a new resource, PUT updates — POST creates new, PUT updates.

Complete the setBody call

client.post(url) {
    ____(user)
}

Show answer

client.post(url) {
    setBody(user)
}

Match POST parts

client.post

Sends request
setBody

Adds body
contentType

Sets type
HttpResponse

Response type

Next lesson: JSON deserialization

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