Sending Data with POST Requests in Kotlin

Sending Data with POST Requests

Welcome to this lesson on sending data with POST requests . As you continue your exploration of interacting with RESTful APIs, you'll learn how to send data to a server using the POST method. POST requests are essential when you want to create new resources or submit data, such as filling out a web form or adding a new entry to a database. Unlike GET requests, which you have already encountered, POST requests do not solely retrieve information; they actually transmit data to an API. Understanding these differences is crucial as you expand your skill set in HTTP methods. Let’s dive deeper into utilizing POST requests to comprehend how they stand apart from GET requests.

Key Differences Between GET and POST

Before diving into POST requests, let's briefly compare them to GET requests: GET Requests : Purpose : Retrieve data from a server. Data Location : Data is sent in the URL as path or query parameters. Success Status : Expect a 200 status code for successful data retrieval. Security and Data Visibility : Data is appended to the URL, making it visible in browser history, server logs, and network tools, which is unsuitable for sensitive information. POST Requests : Purpose : Send data to a server to create or update a resource, such as submitting a form, uploading a file, or adding a new item to a database. Data Location : Data is sent in the request body. Success Status : Expect a 201 status code for successful resource creation. Security and Data Visibility : Data is sent in the request body, making it less exposed and more suitable for transmitting sensitive information. These differences clarify when to use each method. POST requests, in particular, require careful handling of the request body.

Understanding the Request Body

For POST requests, the request body is crucial as it holds the data you want to send to the server. This data is usually structured in formats like JSON, XML, or form data, with JSON being a common choice due to its readability and compatibility. Here's an example of a JSON request body: JSON {"title": "Learn Kotlin OkHttp library", "description": "Complete a course on Kotlin API calls.", "done": false} {"title": "Learn Kotlin OkHttp library", "description": "Complete a course on Kotlin API calls.", "done": false} This represents a new todo item, including a title, completion status, and description. Noticeably, we are not sending an id, as this is typically managed by the server upon resource creation. With a solid understanding of GET vs. POST and the role of the request body, you’re ready to explore how to utilize Kotlin's OkHttp library to handle POST operations.

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JSON

{
  "title": "Learn Kotlin OkHttp library",
  "description": "Complete a course on Kotlin API calls.",
  "done": false
}

Kotlin

// New todo data in JSON format
val newTodo = """
    {
        "title": "Learn Kotlin OkHttp library",
        "description": "Complete a course on Kotlin API calls.",
        "done": false
    }
""".trimIndent()

val client = OkHttpClient()
val mediaType = "application/json; charset=utf-8".toMediaTypeOrNull()
val requestBody = newTodo.toRequestBody(mediaType)

// Build and execute the POST request
val request = Request.Builder()
    .url("$baseUrl/todos")
    .post(requestBody)
    .build()

val response = client.newCall(request).execute()

// New todo data in JSON format
val newTodo = """
    {
        "title": "Learn Kotlin OkHttp library",
        "description": "Complete a course on Kotlin API calls.",
        "done": false
    }
""".trimIndent()

val client = OkHttpClient()
val mediaType = "application/json; charset=utf-8".toMediaTypeOrNull()
val requestBody = newTodo.toRequestBody(mediaType)

// Build and execute the POST request
val request = Request.Builder()
    .url("$baseUrl/todos")
    .post(requestBody)
    .build()

val response = client.newCall(request).execute()

Kotlin

if (response.isSuccessful) {
    if (response.code == 201) {
        println("New todo added successfully!")
        println(response.body?.string() ?: "No response body")
    }
} else {
    // Handle potential errors
    println("Failed to add a new todo")
    println("Status Code: ${response.code}")
    println("Error Details: ${response.body?.string()}")
}

if (response.isSuccessful) {
    if (response.code == 201) {
        println("New todo added successfully!")
        println(response.body?.string() ?: "No response body")
    }
} else {
    // Handle potential errors
    println("Failed to add a new todo")
    println("Status Code: ${response.code}")
    println("Error Details: ${response.body?.string()}")
}

Kotlin

// New todo data with missing title
val incompleteTodo = """
    {
        "done": false,
        "description": "Complete a course on Kotlin API calls."
    }
""".trimIndent()

val requestBodyIncomplete = incompleteTodo.toRequestBody(mediaType)

// Build and execute the POST request
val requestIncomplete = Request.Builder()
    .url("$baseUrl/todos")
    .post(requestBodyIncomplete)
    .build()

val responseIncomplete = client.newCall(requestIncomplete).execute()

if (responseIncomplete.isSuccessful) {
    println("New todo added successfully!")
    println(responseIncomplete.body?.string() ?: "No response body")
} else {
    // Handle potential errors
    println("Failed to add a new todo")
    println("Status Code: ${responseIncomplete.code}")
    println("Error Details: ${responseIncomplete.body?.string()}")
}

// New todo data with missing title
val incompleteTodo = """
    {
        "done": false,
        "description": "Complete a course on Kotlin API calls."
    }
""".trimIndent()

val requestBodyIncomplete = incompleteTodo.toRequestBody(mediaType)

// Build and execute the POST request
val requestIncomplete = Request.Builder()
    .url("$baseUrl/todos")
    .post(requestBodyIncomplete)
    .build()

val responseIncomplete = client.newCall(requestIncomplete).execute()

if (responseIncomplete.isSuccessful) {
    println("New todo added successfully!")
    println(responseIncomplete.body?.string() ?: "No response body")
} else {
    // Handle potential errors
    println("Failed to add a new todo")
    println("Status Code: ${responseIncomplete.code}")
    println("Error Details: ${responseIncomplete.body?.string()}")
}

text

Failed to add a new todo
Status code: 400
Error Details: {"error": "Invalid request. 'title' is required."}

Failed to add a new todo
Status code: 400
Error Details: {"error": "Invalid request. 'title' is required."}

Kotlin

// New todo data in JSON format
val newTodo = """
    {
        "title": "Learn Kotlin OkHttp library",
        "description": "Complete a course on Kotlin API calls.",
        "done": false
    }
""".trimIndent()

val client = OkHttpClient()
val mediaType = "application/json; charset=utf-8".toMediaTypeOrNull()
val requestBody = newTodo.toRequestBody(mediaType)

// Build and execute the POST request
val request = Request.Builder()
    .url("$baseUrl/todos")
    .post(requestBody)
    .build()

val response = client.newCall(request).execute()

Kotlin

if (response.isSuccessful) {
    if (response.code == 201) {
        println("New todo added successfully!")
        println(response.body?.string() ?: "No response body")
    }
} else {
    // Handle potential errors
    println("Failed to add a new todo")
    println("Status Code: ${response.code}")
    println("Error Details: ${response.body?.string()}")
}

Kotlin

// New todo data with missing title
val incompleteTodo = """
    {
        "done": false,
        "description": "Complete a course on Kotlin API calls."
    }
""".trimIndent()

val requestBodyIncomplete = incompleteTodo.toRequestBody(mediaType)

// Build and execute the POST request
val requestIncomplete = Request.Builder()
    .url("$baseUrl/todos")
    .post(requestBodyIncomplete)
    .build()

val responseIncomplete = client.newCall(requestIncomplete).execute()

if (responseIncomplete.isSuccessful) {
    println("New todo added successfully!")
    println(responseIncomplete.body?.string() ?: "No response body")
} else {
    // Handle potential errors
    println("Failed to add a new todo")
    println("Status Code: ${responseIncomplete.code}")
    println("Error Details: ${responseIncomplete.body?.string()}")
}

text

Failed to add a new todo
Status code: 400
Error Details: {"error": "Invalid request. 'title' is required."}

Sending Data with POST Requests

Key Differences Between GET and POST

Understanding the Request Body

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Crafting a POST Request: Adding a New Todo

Handling Responses and Error Management

Example of Unsuccessful POST Request

Summary and Overview of Practice Exercises