GET and POST requests in Android Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What happens when this GET request code runs?

Consider this Kotlin code snippet in an Android app making a GET request. What will be the output in the log if the server responds with status 200 and body "Hello World"?

Android Kotlin

val url = URL("https://example.com/api/greet")
val connection = url.openConnection() as HttpURLConnection
connection.requestMethod = "GET"
val responseCode = connection.responseCode
val response = connection.inputStream.bufferedReader().readText()
Log.d("HTTP", "Code: $responseCode, Body: $response")

A Code: 200, Body: null

B Code: 404, Body: Not Found

C Code: 200, Body: Hello World

D App crashes with IOException

💡 Hint

Think about what responseCode and inputStream return when the server responds successfully.

The code sets the request method to GET, connects to the URL, reads the response code and body. If the server returns 200 and "Hello World", the log will show those values.

📝 Syntax

intermediate

Which option correctly sends a POST request with JSON body?

You want to send a POST request with JSON data in Kotlin Android. Which code snippet correctly sets up the connection and sends the JSON string?

A

val url = URL("https://example.com/api/data")
val conn = url.openConnection() as HttpURLConnection
conn.requestMethod = "POST"
conn.doOutput = true
conn.setRequestProperty("Content-Type", "application/json")
val json = "{\"name\":\"John\"}"
conn.outputStream.write(json.toByteArray())

B

val url = URL("https://example.com/api/data")
val conn = url.openConnection() as HttpURLConnection
conn.requestMethod = "POST"
val json = "{\"name\":\"John\"}"
conn.outputStream.write(json.toByteArray())

C

val url = URL("https://example.com/api/data")
val conn = url.openConnection() as HttpURLConnection
conn.requestMethod = "GET"
conn.doOutput = true
val json = "{\"name\":\"John\"}"
conn.outputStream.write(json.toByteArray())

D

val url = URL("https://example.com/api/data")
val conn = url.openConnection() as HttpURLConnection
conn.requestMethod = "POST"
conn.doInput = true
conn.setRequestProperty("Content-Type", "application/json")
val json = "{\"name\":\"John\"}"
conn.outputStream.write(json.toByteArray())

💡 Hint

Remember to enable output and set the content type for JSON when sending POST data.

Option A correctly sets requestMethod to POST, enables output with doOutput=true, sets Content-Type header, and writes JSON bytes to outputStream.

❓ lifecycle

advanced

What is the risk of running network requests on the main thread?

In Android Kotlin, what happens if you run a GET or POST request on the main UI thread?

A The app crashes immediately with a NullPointerException

B The app UI freezes and may show an Application Not Responding (ANR) error

C The request runs faster because it uses the main thread

D Nothing special happens; network requests are safe on the main thread

💡 Hint

Think about what happens when the UI thread is blocked for too long.

Network requests can take time. Running them on the main thread blocks UI updates, causing the app to freeze and possibly trigger an ANR error.

🔧 Debug

advanced

Why does this POST request code throw a ProtocolException?

This Kotlin code throws java.net.ProtocolException: cannot write output after reading input. Why?

Android Kotlin

val url = URL("https://example.com/api/post")
val conn = url.openConnection() as HttpURLConnection
conn.requestMethod = "POST"
conn.doOutput = true
val response = conn.inputStream.bufferedReader().readText()
conn.outputStream.write("data".toByteArray())

A Because requestMethod POST is invalid for this URL

B Because doOutput must be false for POST requests

C Because outputStream.write() requires a flush() call first

D Because inputStream was read before enabling output and writing data

💡 Hint

Check the order of reading input and writing output streams.

You must write data to outputStream before reading inputStream. Reading inputStream first locks the connection and causes ProtocolException.

🧠 Conceptual

expert

How to handle JSON response parsing after a GET request?

After a successful GET request returning JSON data, which approach correctly parses the JSON string into a Kotlin data class?

Android Kotlin

data class User(val id: Int, val name: String)

val jsonResponse = "{\"id\":1, \"name\":\"Alice\"}"

A val user = Gson().fromJson(jsonResponse, User::class.java)

B val user = jsonResponse.toString() as User

C val user = User(jsonResponse["id"], jsonResponse["name"])

D val user = JSONObject(jsonResponse).toString()

💡 Hint

Use a JSON library to convert JSON string to Kotlin objects.

Gson().fromJson() correctly parses JSON string into the User data class. Other options either cause errors or do not parse JSON properly.