Data Parsing and Scraping in Kotlin: From Beginner to Real Project

Data Parsing and Scraping in Kotlin: Why It's Worth Your Attention

When it comes to collecting data from the internet, Python with its BeautifulSoup and Scrapy usually comes to mind first. But what if your stack is JVM and your heart is set on concise and safe code? Meet Kotlin. This language is not just "another Java," but a powerful tool for data parsing and scraping that allows you to write clean, performant, and asynchronous code without unnecessary noise.

In this article, we'll break down how to turn Kotlin into a real data collection machine. You'll learn which libraries to use, how to avoid getting banned from a website, and how to process thousands of pages without a headache. Let's go!

What is Data Parsing and Scraping in Kotlin

Before diving into the code, let's dot the i's and cross the t's.

• Web scraping is the mass extraction of data from web pages. You download HTML, parse it, and extract the pieces you need: prices, titles, product descriptions.
• Parsing is a narrower concept. It is the process of analyzing a data structure (HTML, JSON, XML) into a form convenient for a program. Parsing is a part of scraping.

In Kotlin, data parsing and scraping are implemented elegantly thanks to functional capabilities, strong typing, and excellent coroutine support. You get code that is easy to read, test, and maintain.

Libraries for Data Parsing and Scraping in Kotlin

Choosing the right library is 50% of success. Here is the essential toolkit for Kotlin:

• Jsoup — the gold standard for HTML parsing. Works on JVM, handles even messy markup.
• Ktor Client — an asynchronous HTTP client from JetBrains. Perfect for use with coroutines.
• kotlinx.serialization — painless JSON serialization.
• OkHttp — if you need more low-level control over requests.
• HtmlUnit — for websites that render content via JavaScript (rare, but it happens).

In this article, we will focus on the Ktor + Jsoup + kotlinx.serialization stack — it provides maximum control and speed.

Practical Example: Parsing Data from a Website in Kotlin

The best way to understand data scraping in Kotlin is to write a real script. Let's imagine we are collecting information about books from an aggregator website (e.g., Habr or an online bookstore). Our goal: get the title, author, and price of each book.

Step 1. Project Setup

Create a new Gradle project and add dependencies to build.gradle.kts:

dependencies {    implementation("io.ktor:ktor-client-core:2.3.7")    implementation("io.ktor:ktor-client-cio:2.3.7")    implementation("org.jsoup:jsoup:1.17.2")    implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.6.2")    implementation("ch.qos.logback:logback-classic:1.4.14")}

Step 2. Writing an HTTP Client for Loading Pages

We use Ktor Client for asynchronous loading. Coroutines allow us to do this without blocking the thread.

import io.ktor.client.*import io.ktor.client.request.*import io.ktor.client.statement.*import kotlinx.coroutines.runBlocking

class PageLoader(private val client: HttpClient) {

    suspend fun loadPage(url: String): String {        val response: HttpResponse = client.get(url)        return response.bodyAsText()    }}

fun main() = runBlocking {    val client = HttpClient {        // can configure timeouts, user agents, etc.    }    val loader = PageLoader(client)    val html = loader.loadPage("https://example-books.com/catalog")    println(html.take(500)) // print first 500 characters for verification    client.close()}

Step 3. Par