Processing CSV Files Using Kotlin’s File API

In this article, we will explore how to efficiently process CSV files using Kotlin’s File API. The flexibility and power of these API allow you to read, write, and manipulate CSV data seamlessly in a Kotlin application.

Getting Started with Kotlin’s File API

Kotlin's File API is included as part of the Kotlin standard library, and it provides several extensions around java.io.File class to handle file systems. To process CSV files, we ensure that our project has no special dependencies other than the JVM itself.

Reading CSV Files

To read a CSV file, you generally open the file, read its contents line-by-line, and parse it according to CSV format conventions.

Here is a basic example to read a CSV file:

import java.io.File

fun readCsv(fileName: String): List> {
    val file = File(fileName)
    return file.readLines()
        .map { line -> line.split(";") }
}

fun main() {
    val csvData = readCsv("data.csv")
    for (row in csvData) {
        println(row)
    }
}

Explanation:

• File(fileName) creates a File object from the given path.
• readLines() reads the file line by line and returns a list of strings.
• Each line is split by the delimiter, ";", into a list representing a CSV row.

Writing to CSV Files

Writing to a CSV file in Kotlin is straightforward using the File API. Here, we'll see how you can transfer a list of data into a CSV format and write it to the file system.

fun writeCsv(fileName: String, data: List>) {
    val file = File(fileName)
    file.printWriter().use { out ->
        data.forEach { row ->
            out.println(row.joinToString(separator = ";"))
        }
    }
}

fun main() {
    val data = listOf(
        listOf("Name", "Age", "City"),
        listOf("Alice", "30", "New York"),
        listOf("Bob", "25", "Los Angeles")
    )
    writeCsv("output.csv", data)
}

Explanation:

• A PrintWriter is used here, which provides buffering and convenient handling of character data output.
• The joinToString() extension function converts an array or list into a string separated by specified characters, which is precisely what you need to format a CSV line.

Error Handling and Exceptions

While working with files, proper handling of I/O exceptions is crucial. Kotlin, while offering null safety, still relies on traditional try-catch blocks to handle potential file access related exceptions.

try {
    val data = readCsv("nonexistent.csv")
    data.forEach { println(it) }
} catch (e: Exception) {
    println("An error occurred: ")
    e.printStackTrace()
}

This code ensures that any file access or parsing anomalies do not cause abrupt application termination.

Conclusion

Handling CSV files in Kotlin with its File API provides an intuitive approach to manage data with the syntax we’ve explored. Whether reading or writing, you'll find these methods easy to adapt and integrate into your projects. Mastery of these techniques can greatly enhance the efficiency and reliability of your data-driven applications.