Kotlin Read from File

core-kotlin/src/main/kotlin/com/baeldung/filesystem/FileReader.kt

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+package com.baeldung.filesystem
+
+import java.io.BufferedReader
+import java.io.File
+import java.io.InputStream
+import java.nio.charset.StandardCharsets
+
+class FileReader {
+
+    fun readFileLineByLineUsingForEachLine(fileName: String): List<String> {
+        val lineList = mutableListOf<String>()
+        File(fileName).forEachLine { line -> lineList.add(line) }
+        return lineList
+    }
+
+    fun readFileAsLinesUsingUseLines(fileName: String): List<String> {
+        val lineList = mutableListOf<String>()
+        File(fileName).useLines { lines -> lineList.addAll(lines) }
+        return lineList
+    }
+
+    fun readFileAsLinesUsingBufferedReader(fileName: String): List<String> {
+        val bufferedReader: BufferedReader = File(fileName).bufferedReader()
+        return bufferedReader.readLines()
+    }
+
+    fun readFileAsLinesUsingReadLines(fileName: String): List<String> {
+        return File(fileName).readLines(StandardCharsets.UTF_8)
+    }
+
+    fun readFileAsTextUsingInputStream(fileName: String): String {
+        val inputStream: InputStream = File(fileName).inputStream()
+        return inputStream.readBytes().toString(StandardCharsets.UTF_8)
+    }
+
+    fun readFileDirectlyAsText(fileName: String): String {
+        return File(fileName).readText(StandardCharsets.UTF_8)
+    }
+
+}

core-kotlin/src/test/kotlin/com/baeldung/filesystem/FileReaderTest.kt

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+package com.baeldung.filesystem
+
+import org.junit.jupiter.api.Test
+import kotlin.test.assertTrue
+
+internal class FileReaderTest {
+
+    private val fileName = "src/test/resources/Kotlin.in"
+
+    private val fileReader = FileReader()
+
+    @Test
+    fun whenReadFileLineByLineUsingForEachLine_thenCorrect() {
+        val lines = fileReader.readFileLineByLineUsingForEachLine(fileName)
+
+        assertTrue { lines.contains("Hello to Kotlin. Its:") }
+    }
+
+    @Test
+    fun whenReadFileAsLinesUsingUseLines_thenCorrect() {
+        val lines = fileReader.readFileAsLinesUsingUseLines(fileName)
+
+        assertTrue { lines.contains("1. Concise") }
+    }
+
+    @Test
+    fun whenReadFileAsLinesUsingBufferedReader_thenCorrect() {
+        val lines = fileReader.readFileAsLinesUsingBufferedReader(fileName)
+
+        assertTrue { lines.contains("2. Safe") }
+    }
+
+    @Test
+    fun whenReadFileAsLinesUsingReadLines_thenCorrect() {
+        val lines = fileReader.readFileAsLinesUsingReadLines(fileName)
+
+        assertTrue { lines.contains("3. Interoperable") }
+    }
+
+    @Test
+    fun whenReadFileAsTextUsingInputStream_thenCorrect() {
+        val text = fileReader.readFileAsTextUsingInputStream(fileName)
+
+        assertTrue { text.contains("4. Tool-friendly") }
+    }
+
+    @Test
+    fun whenReadDirectlyAsText_thenCorrect() {
+        val text = fileReader.readFileDirectlyAsText(fileName)
+
+        assertTrue { text.contains("Hello to Kotlin") }
+    }
+}

core-kotlin/src/test/resources/Kotlin.in

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+Hello to Kotlin. Its:
+1. Concise
+2. Safe
+3. Interoperable
+4. Tool-friendly