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.

Practice

1. What is the main purpose of a GET request in Android Kotlin networking?

easy

A. To fetch data from a server

B. To send data to a server

C. To update the UI thread

D. To store data locally

Solution

1. Step 1: Understand GET request purpose

   A GET request is used to retrieve or fetch data from a server without changing any data on the server.

2. Step 2: Compare with other request types

   POST requests send data to the server, unlike GET which only fetches data.

3. Final Answer:

   To fetch data from a server -> Option A

4. Quick Check:

   GET = fetch data [OK]

Hint: GET fetches data; POST sends data [OK]

Common Mistakes:

• Confusing GET with POST request purpose
• Thinking GET modifies server data
• Mixing UI updates with network requests

2. Which of the following is the correct way to start a POST request using Kotlin's HttpURLConnection?

easy

A. connection.requestMethod = "GET"

B. connection.requestMethod = "POST"

C. connection.method = "POST"

D. connection.setRequestMethod("GET")

Solution

1. Step 1: Identify correct property for request method

   In Kotlin, HttpURLConnection uses requestMethod property to set the HTTP method.

2. Step 2: Confirm correct method value for POST

   To make a POST request, set requestMethod to "POST" exactly.

3. Final Answer:

   connection.requestMethod = "POST" -> Option B

4. Quick Check:

   POST method set by requestMethod = "POST" [OK]

Hint: Use requestMethod property with "POST" string [OK]

Common Mistakes:

• Using wrong property name like method
• Setting GET instead of POST
• Using Java-style setRequestMethod() in Kotlin

3. What will be the output of this Kotlin code snippet when making a GET request?

val url = URL("https://example.com/data")
val connection = url.openConnection() as HttpURLConnection
connection.requestMethod = "GET"
val responseCode = connection.responseCode
println(responseCode)

medium

A. 500

B. 404

C. 200

D. Compilation error

Solution

1. Step 1: Understand the code flow

   The code opens a connection to the URL and sets the method to GET, then reads the response code from the server.

2. Step 2: Predict typical HTTP response code

   Assuming the URL is valid and reachable, a successful GET request returns HTTP status code 200.

3. Final Answer:

   200 -> Option C

4. Quick Check:

   Successful GET returns 200 [OK]

Hint: 200 means OK response from server [OK]

Common Mistakes:

• Assuming responseCode is a string
• Confusing 404 (not found) with success
• Thinking code will not compile

4. Identify the error in this Kotlin code snippet for sending a POST request:

val url = URL("https://example.com/api")
val connection = url.openConnection() as HttpURLConnection
connection.requestMethod = "POST"
val outputStream = connection.outputStream
outputStream.write("data=hello".toByteArray())
outputStream.flush()
outputStream.close()

medium

A. Missing setting connection.doOutput = true

B. Using write() instead of writeBytes()

C. Incorrect requestMethod value

D. Not reading the response code

Solution

1. Step 1: Check POST request setup

   For POST requests, doOutput must be set to true to send data in the request body.

2. Step 2: Identify missing property

   The code does not set connection.doOutput = true, so writing to outputStream will fail or not send data.

3. Final Answer:

   Missing setting connection.doOutput = true -> Option A

4. Quick Check:

   doOutput = true needed for POST body [OK]

Hint: Set doOutput true before writing POST data [OK]

Common Mistakes:

• Forgetting doOutput = true for POST
• Confusing write() method usage
• Ignoring response reading after POST

5. You want to send JSON data in a POST request using Kotlin. Which sequence correctly sets up the connection and sends the JSON string {"name":"John"}?

hard

A. Set requestMethod to "GET", write JSON bytes to outputStream, set doOutput = true

B. Set requestMethod to "POST", set doOutput = false, write JSON string directly to connection

C. Set requestMethod to "POST", write JSON bytes to outputStream without setting doOutput, set Content-Type header to "text/plain"

D. Set requestMethod to "POST", set doOutput = true, set Content-Type header to "application/json", write JSON bytes to outputStream

Solution

1. Step 1: Correct HTTP method and output setup

   For sending data, requestMethod must be "POST" and doOutput must be true to allow writing data.

2. Step 2: Set proper headers and write data

   Content-Type header should be "application/json" to indicate JSON data. Then write JSON bytes to outputStream.

3. Final Answer:

   Set requestMethod to "POST", set doOutput = true, set Content-Type header to "application/json", write JSON bytes to outputStream -> Option D

4. Quick Check:

   POST + doOutput + JSON header + write bytes [OK]

Hint: POST JSON needs doOutput true and JSON content-type [OK]

Common Mistakes:

• Using GET method to send data
• Not setting Content-Type header correctly
• Forgetting doOutput = true