CODEWITHSUNDEEP
filekotlintext-filesbufferedreader
Anisuzzaman Babla
Anisuzzaman Babla

Reputation: 7480

How to read plain text file in kotlin?

There may be various way to read plain text file in kotlin.

I want know what are the possible ways and how I can use them.

Upvotes: 49

Views: 76677

Answers (7)

Leonid Ivankin
Leonid Ivankin

Reputation: 667

fun main() {
val inputString = File("file.csv")
    .bufferedReader()
    .use { it.readText() }
println(inputString)
}

Upvotes: 0

Gee
Gee

Reputation: 1

how to apply Documents path on that:

fun main(args: Array<String>) {
        val inputStream: InputStream = File("example.txt").inputStream()
        val inputString = inputStream.bufferedReader().use { it.readText() }
        println(inputString)
    }

Upvotes: 0

katsusuke
katsusuke

Reputation: 571

I think the simplest way to code is using kotlin.text and java.io.File

import java.io.File

fun main(args: Array<String>) {
    val text = File("sample.txt").readText()
    println(text)
}

Upvotes: 37

Anisuzzaman Babla
Anisuzzaman Babla

Reputation: 7480

1. Using BufferedReader

    import java.io.File
    import java.io.BufferedReader

    fun main(args: Array<String>) {
        val bufferedReader: BufferedReader = File("example.txt").bufferedReader()    
        val inputString = bufferedReader.use { it.readText() }
        println(inputString)
    }

2. Using InputStream

Read By Line

    import java.io.File
    import java.io.InputStream

    fun main(args: Array<String>) {
        val inputStream: InputStream = File("example.txt").inputStream()
        val lineList = mutableListOf<String>()

        inputStream.bufferedReader().forEachLine { lineList.add(it) } 
        lineList.forEach{println(">  " + it)}
    }

Read All Lines

    import java.io.File
    import java.io.InputStream

    fun main(args: Array<String>) {
        val inputStream: InputStream = File("example.txt").inputStream()
        val inputString = inputStream.bufferedReader().use { it.readText() }
        println(inputString)
    }

3. Use File directly

    import java.io.File
    import java.io.BufferedReader

    fun main(args: Array<String>) {
        val lineList = mutableListOf<String>()

        File("example.txt").useLines { lines -> lines.forEach { lineList.add(it) }}
        lineList.forEach { println(">  " + it) }
    }

Upvotes: 85

Greg Supina
Greg Supina

Reputation: 31

To read a text file, it must first be created. In Android Studio, you would create the text file like this:

1) Select "Project" from the top of the vertical toolbar to open the project "tool window" 2) From the drop-down menu at the top of the "tool window", select "Android" 3) Right-click on "App" and select "New" then -> "Folder" (the one with the green Android icon beside it) then -> "Assets Folder" 4) Right-click on the "assets" folder after it appears in the "tool window" 5) Select "New" -> "File" 6) Name the file, and included the extension ".txt" if it is text file, or ".html" if it is for WebView 7) Edit the file or cut and paste text into it. The file will now display under the "Project" files in the "tool window" and you will be able to double-click it to edit it at any time.

TO ACCESS THIS FILE, use a prefix of "application.assets." followed by someFunction(fileName). For example (in Kotlin):

val fileName = "townNames.txt"
val inputString = application.assets.open(fileName).bufferedReader().use { it.readText() }
val townList: List<String> = inputString.split("\n")

Upvotes: 3

Simon Schubert
Simon Schubert

Reputation: 2028

The answers above here are all based on Kotlin Java. Here is a Kotlin Native way to read text files:

val bufferLength = 64 * 1024
val buffer = allocArray<ByteVar>(bufferLength)

 for (i in 1..count) {
    val nextLine = fgets(buffer, bufferLength, file)?.toKString()
    if (nextLine == null || nextLine.isEmpty()) break

    val records = parseLine(nextLine, ',')
    val key = records[column]
    val current = keyValue[key] ?: 0
    keyValue[key] = current + 1
}


fun parseLine(line: String, separator: Char) : List<String> {
    val result = mutableListOf<String>()
    val builder = StringBuilder()
    var quotes = 0
    for (ch in line) {
        when {
            ch == '\"' -> {
                quotes++
                builder.append(ch)
            }
            (ch == '\n') || (ch ==  '\r') -> {}
            (ch == separator) && (quotes % 2 == 0) -> {
                result.add(builder.toString())
                builder.setLength(0)
            }
            else -> builder.append(ch)
        }
    }
    return result
}

See: https://github.com/JetBrains/kotlin-native/blob/master/samples/csvparser/src/csvParserMain/kotlin/CsvParser.kt

Upvotes: 7

gidds
gidds

Reputation: 18557

Anisuzzaman's answer lists several possibilities.

The main differences between them are in whether the file is read into memory as a single String, read into memory and split into lines, or read line-by-line.

Obviously, reading the entire file into memory in one go can take a lot more memory, so that's something to avoid unless it's really necessary.  (Text files can get arbitrarily big!)  So processing line-by-line with BufferedReader.useLines() is often a good approach.

The remaining differences are mostly historical.  Very early versions of Java used InputStream &c which didn't properly distinguish between characters and bytes; Reader &c were added to correct that.  Java 8 added ways to read line-by-line more efficiently using streams (e.g. Files.lines()).  And more recently, Kotlin has added its own extension functions (e.g. BufferedReader.useLines()) which make it even simpler.

Upvotes: 8

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