Web scraping is useful to programmatically extract data from websites. Often you need to scrape multiple pages from a site to gather complete information. In this article, we'll see how to scrape multiple pages in Kotlin using the native HTTP client and kotlinx.html libraries.
Prerequisites
To follow along, you'll need:
implementation("org.jetbrains.kotlinx:kotlinx-html-jvm:0.7.3")
Import Libraries
We'll need the following imports:
import kotlinx.html.*
import kotlinx.html.dom.*
import java.net.HttpURLConnection
Define Base URL
—
We'll scrape a blog -
<https://copyblogger.com/blog/>
<https://copyblogger.com/blog/page/2/>
<https://copyblogger.com/blog/page/3/>
Let's define the base URL pattern:
val baseUrl = "<https://copyblogger.com/blog/page/%d/>"
The
Specify Number of Pages
Next, we'll specify how many pages to scrape. Let's scrape the first 5 pages:
val numPages = 5
Loop Through Pages
We can now loop from 1 to
for (page in 1..numPages) {
// Construct page URL
val url = baseUrl.format(page)
// Code to scrape each page
}
Send Request and Parse HTML
Inside the loop, we'll send a GET request and parse the HTML:
val connection = URL(url).openConnection() as HttpURLConnection
connection.inputStream.bufferedReader().use {
val doc = it.readText()
val parsed = parse(doc)
}
This gives us a parsed HTML document to extract data from.
Extract Data
Now within the loop we can use CSS selectors to find and extract data from each page:
for (article in parsed.select("article")) {
// Extract data from article
val title = article.select("h2.entry-title").text()
val url = article.select("a.entry-title-link").attr("href")
val author = article.select("div.post-author a").text()
}
Full Code
Our full code to scrape 5 pages is:
You're absolutely right, I missed extracting the categories in my Kotlin web scraping example. Here is the updated full code including fetching the categories:
```kotlin
import kotlinx.html.*
import kotlinx.html.dom.*
import java.net.HttpURLConnection
fun main() {
val baseUrl = "https://copyblogger.com/blog/page/%d/"
val numPages = 5
for (page in 1..numPages) {
val url = baseUrl.format(page)
val connection = URL(url).openConnection() as HttpURLConnection
connection.inputStream.bufferedReader().use {
val doc = it.readText()
val parsed = parse(doc)
for (article in parsed.select("article")) {
val title = article.select("h2.entry-title").text()
val url = article.select("a.entry-title-link").attr("href")
val author = article.select("div.post-author a").text()
val categories = article.select("div.entry-categories a").map { it.text() }
println("Title: $title")
println("URL: $url")
println("Author: $author")
println("Categories: $categories")
}
}
}
}
```
I've added the missing code to extract the categories into a list and print it. Let me know if you need any other changes to the Kotlin scraping example!This allows us to scrape and extract data from multiple pages sequentially. The code can be extended to scrape any number of pages.
Summary
Web scraping enables collecting large datasets programmatically. With the techniques here, you can scrape and extract information from multiple pages of a website in Kotlin.
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