· tutorials · 5 min read

How To Convert HTML to PDF with Kotlin

Dive deep into the efficient methodologies for converting HTML to PDF in Kotlin, ensuring your project leverages the best available tools.

Dive deep into the efficient methodologies for converting HTML to PDF in Kotlin, ensuring your project leverages the best available tools.

Introduction

In the digital age, the need to convert dynamic HTML content into a static PDF format is common across various applications, including generating reports, invoices, and other document types. Kotlin, with its concise syntax and interoperability with Java, offers a modern approach to tackle this task. This guide delves into several efficient techniques and tools for converting HTML to PDF, specifically tailored for Kotlin developers.

Why Choose HTML to PDF Conversion?

The decision to convert HTML to PDF is driven by several compelling reasons:

  • Universality of HTML: HTML stands as the cornerstone of web content, offering a wide familiarity among developers. Utilizing HTML as a starting point for PDF generation taps into this universal knowledge base.
  • Robust Support Network: The longevity and prevalence of HTML have fostered a comprehensive support network, ensuring developers have access to extensive resources and community expertise.
  • Diverse Toolkit: The landscape of HTML to PDF conversion tools is rich and varied, providing options that cater to different needs, from simple document conversions to complex, design-rich publications.
  • CSS for Customization: CSS empowers developers to style PDFs with the same degree of customization and precision as web pages, ensuring the final documents meet exact design specifications.
  • Media-Rich Content: HTML’s capability to embed multimedia elements means that converted PDFs can retain a dynamic quality, incorporating images, hyperlinks, and more.

HTML to PDF using Kotlin Libraries

1. OpenPDF

OpenPDF, a successor to iText, is a notable open-source library that specializes in creating and manipulating PDF content. It provides a straightforward API for converting HTML to PDF in a Kotlin environment.

Step 1: Add OpenPDF Dependency

Incorporate OpenPDF into your Kotlin project by adding the dependency to your pom.xml:

<dependency>
    <groupId>com.github.librepdf</groupId>
    <artifactId>openpdf</artifactId>
    <version>1.3.26</version>
</dependency>

Step 2: Kotlin Code to Convert HTML to PDF

A simple Kotlin example to demonstrate HTML to PDF conversion using OpenPDF:

import com.lowagie.text.Document
import com.lowagie.text.Paragraph
import com.lowagie.text.html.simpleparser.HTMLWorker
import com.lowagie.text.pdf.PdfWriter
import java.io.FileOutputStream
import java.io.StringReader


fun main() {
    Document().apply {
        PdfWriter.getInstance(this, FileOutputStream("HtmlToPdf.pdf"))
        open()
        HTMLWorker(this).parse(StringReader("<html><body>This is my Project</body></html>"))
        close()
    }
    println("PDF created successfully.")
}

2. Flying Saucer

Flying Saucer excels in rendering XHTML/CSS content to PDF. It’s an excellent choice for projects requiring precise layout and styling fidelity.

Step 1: Add Flying Saucer Dependency

To use Flying Saucer, add these dependencies:

<dependency>
    <groupId>org.xhtmlrenderer</groupId>
    <artifactId>flying-saucer-core</artifactId>
    <version>9.1.22</version>
</dependency>
<dependency>
    <groupId>org.xhtmlrenderer</groupId>
    <artifactId>flying-saucer-pdf</artifactId>
    <version>9.1.22</version>
</dependency>

Step 2: Kotlin Code to Convert HTML to PDF

The following Kotlin code snippet uses Flying Saucer to render an XHTML file to PDF:

import org.xhtmlrenderer.pdf.ITextRenderer
import java.io.FileOutputStream
import java.io.File


fun main() {
    ITextRenderer().apply {
        setDocument(File("input.html"))
        layout()
        createPDF(FileOutputStream("output.pdf"))
    }
    println("PDF created successfully with Flying Saucer.")
}

3. iText

iText is a versatile library that not only facilitates HTML to PDF conversions but also offers extensive PDF manipulation capabilities.

Step 1: Add iText Dependency

Include iText by adding it to your pom.xml:

<dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>html2pdf</artifactId>
    <version>3.0.1</version>
</dependency>

Step 2: Kotlin Code to Convert HTML to PDF

This example demonstrates converting HTML to PDF with iText:

import com.itextpdf.html2pdf.HtmlConverter
import java.io.FileInputStream
import java.io.FileOutputStream


fun main() {
    HtmlConverter.convertToPdf(FileInputStream("input.html"), FileOutputStream("output.pdf"))
    println("PDF generated successfully with iText.")
}

Leveraging Templated for Advanced HTML to PDF Conversion

While the libraries above offer great solutions for HTML to PDF conversion, managing complex templates or producing documents at scale can be challenging. Templated provides a powerful and easy-to-use API for generating PDFs from HTML templates, ideal for automating document generation processes in Kotlin applications.

This approach simplifies the process and eliminates the need for extensive manual template management and tracking. To get started with PDF generation using Templated, follow the documentation and harness the power of this efficient solution.

Using Templated API with Kotlin

Setting Up Templated API

First, obtain your API key from Templated and include the Templated API dependency in your project:

// Define your Templated API Key
val apiKey = "YOUR_API_KEY_HERE"

Kotlin Example to Generate PDF with Templated

The following Kotlin snippet demonstrates generating a PDF using Templated’s API:

import java.net.HttpURLConnection
import java.net.URL


fun main() {
    val apiUrl = "https://api.templated.io/v1/render"
    val apiKey = "YOUR_API_KEY_HERE"
    val jsonInputString = """
        {
            "template": "YOUR_TEMPLATE_ID",
            "layers": {
                "key": "value"
            }
        }
    """.trimIndent()


    with(URL(apiUrl).openConnection() as HttpURLConnection) {
        requestMethod = "POST"
        setRequestProperty("Content-Type", "application/json; utf-8")
        setRequestProperty("Accept", "application/json")
        setRequestProperty("Authorization", "Bearer $apiKey")
        doOutput = true
        outputStream.use { os -> os.write(jsonInputString.toByteArray()) }


        println("Response Code: $responseCode")
        inputStream.bufferedReader().use { reader ->
            println("Response: ${reader.readText()}")
        }
    }
}

This code sends a POST request to Templated’s API, specifying the template and data for PDF generation. Replace "YOUR_TEMPLATE_ID" with the actual ID of your template in Templated.

From your Dashboard, you can design your own templates or customize a existing one from our Template Gallery. Bellow is the Certificate of Achievement Template you can use.
There are 100+ free templates available that you can pick and customize to your needs.

Shows the certicate template in the Template Editor

Other languages

You you want to learn how to convert HTML to PDF in other languages here are other resources for you to explore:

Conclusion

The shift towards digital document management underscores the necessity of efficient HTML to PDF conversion tools. Kotlin developers have a range of libraries at their disposal, each offering unique benefits. For complex or high-volume document generation needs, Templated’s API presents a streamlined, powerful solution.

By leveraging the right tools and approaches, developers can simplify the document generation process, enhance productivity, and focus on creating value in their applications.

Remember to explore Templated’s comprehensive documentation to fully utilize its capabilities for your document generation needs.

To get started, sign up for a free account and begin automating your PDFs today!

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