Kotlin read file bytes

Read a file in Kotlin

This article covers different ways to read the contents of a file in Kotlin.

1. Using BufferedReader.lines() function

In Kotlin, you can use the BufferedReader.lines() function to get a Stream of lines of text read from BufferedReader .

2. Using Files.lines() function

Alternatively, you can use the Files.lines() function to read all lines from a file using the specified charset.

3. Using Files.readAllLines() function

Another plausible way to read all lines from a file using the specified charset is to use the Files.readAllLines() function.

4. Using Files.readAllBytes() function

Another alternative is to use the readAllBytes() function, which returns a byte array having the bytes read from the specified file. To get a string out of file contents, you can pass the byte array to the String constructor.

5. Using Files.readString() function

Finally, you can also use the Files.readString() function to read all characters from a file into a string using the specified charset.

That’s all about reading a file in Kotlin.

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Kotlin Read File

Kotlin Read File – We can read the contents of a file in Kotlin either by using standard methods of the java.io.File class, or the methods that Kotlin provides as an extension to java.io.File.

We shall look into example programs for the extension methods, provided by Kotlin to Java‘s java.io.File Class, to read the contents of a file.

Example programs to read contents of a file in Kotlin

• File.bufferedReader() : To read contents of a file into BufferedReader
• File.forEachLine() : To read a file line by line in Kotlin
• File.inputStream() : To read contents of file to InputStream
• File.readBytes() : To read contents of file to ByteArray
• File.readLines() : To read lines in file to List of String
• File.readText() : To read contents of file to a single String

File.bufferedReader() : How to read contents of a file into BufferedReader

1. Prepare file object with the location of the file passed as argument to File class constructor.
2. File.bufferedReader returns a new BufferedReader for reading the content of the file.
3. Use BufferedReader.readLines() to read the content of the file.

Kotlin Program – example.kt

import java.io.File /** * Created by www.tutorialkart.com * Example program to read contents of a file in Kotlin into BufferedReader */ fun main(args: Array) < val file = File("input"+File.separator+"contents.txt") val bufferedReader = file.bufferedReader() val text:List= bufferedReader.readLines() for(line in text) < println(line) >>

Good Day ! Welcome to Kotlin Tutorials in www.tutorialkart.com. Learn Kotlin easily here. Happy learning. Process finished with exit code 0

Content of file is printed to the console.

File.forEachLine() : Read a file line by line in Kotlin

1. Prepare file object with the location passed as argument to File constructor.
2. Use File.forEachLine function and read each line of the file.

Kotlin Program – example.kt

import java.io.File /** * Created by www.tutorialkart.com * Example program to read contents of a file in Kotlin line by line */ fun main(args: Array) < val file = File("input"+File.separator+"contents.txt") file.forEachLine < println(it) >>

Good Day ! Welcome to Kotlin Tutorials in www.tutorialkart.com. Learn Kotlin easily here. Happy learning Kotlin. Process finished with exit code 0

Content of file is printed to the console.

File.inputStream() : Read contents of file to InputStream

1. Prepare file object with the location of the file passed as argument to File class constructor.
2. File.inputStream() returns a new InputStream for the file.
3. Then you can read bytes from the stream and convert it to a String. This string is content of the file.

Read Content of File to InputStream and then to a String

Kotlin Program – example.kt

import java.io.File import java.io.InputStream /** * Created by www.tutorialkart.com * Example program to read contents of a file in Kotlin to InputStream */ fun main(args: Array) < val file = File("input"+File.separator+"contents.txt") var ins:InputStream = file.inputStream() // read contents of IntputStream to String var content = ins.readBytes().toString(Charset.defaultCharset()) println(content) >

Content of file is printed to the console.

File.readBytes() : returns entire content of file as a ByteArray

1. Prepare file object with the location passed as argument to File constructor.
2. Use File.readBytes() function to get ByteArray. This byte array contains all the file contents.
3. Use for loop to iterate over the byte array and access the contents of file byte by byte.

Kotlin Program – example.kt

import java.io.File /** * Created by www.tutorialkart.com */ fun main(args: Array) < val file = File("input"+File.separator+"contents.txt") var bytes:ByteArray = file.readBytes() for(byte in bytes)< print(byte.toChar()) >>

Content of file is printed to the console.

File.readLines() : returns entire content of file as a List of lines

1. Prepare file object with the location passed as argument to File constructor.
2. Use File.readLines() function to get all the lines in the text file as List of Strings.
3. You can access the list using for loop to read each line of the file.

Kotlin Program – example.kt

import java.io.File /** * Created by www.tutorialkart.com */ fun main(args: Array) < val file = File("input"+File.separator+"contents.txt") var lines:List= file.readLines() for(line in lines) < println(line) >>

Content of file is printed to the console.

File.readText() : returns entire content of file as a single string

You can also read whole content of the file as a single string. Follow these steps.

1. Prepare file object with the location passed as argument to File constructor.
2. Use File.readText() function that returns entire content of file as a String.

Kotlin Program – example.kt

import java.io.File /** * Created by www.tutorialkart.com */ fun main(args: Array)

Content of file is printed to the console.

Conclusion

In this Kotlin Tutorial – Kotlin Read File, we have learned to read the contents of a file in Kotlin, read a file to a byte array, read a file to InputStream, read a file to list of strings, read a file line by line, read a file to BufferedReader.

Related Tutorials

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Kotlin read file bytes

Returns a new BufferedWriter for writing the content of this file.

fun File . bufferedWriter (
charset : Charset = Charsets.UTF_8 ,
bufferSize : Int = DEFAULT_BUFFER_SIZE
) : BufferedWriter

copyRecursively

Copies this file with all its children to the specified destination target path. If some directories on the way to the destination are missing, then they will be created.

fun File . copyRecursively (
target : File ,
overwrite : Boolean = false ,
onError : ( File , IOException ) -> OnErrorAction = < _, exception ->throw exception >
) : Boolean

copyTo

Copies this file to the given target file.

fun File . copyTo (
target : File ,
overwrite : Boolean = false ,
bufferSize : Int = DEFAULT_BUFFER_SIZE
) : File

deleteRecursively

Delete this file with all its children. Note that if this operation fails then partial deletion may have taken place.

endsWith

Determines whether this file path ends with the path of other file.

Determines whether this file belongs to the same root as other and ends with all components of other in the same order. So if other has N components, last N components of this must be the same as in other. For relative other, this can belong to any root.

extension

Returns the extension of this file (not including the dot), or an empty string if it doesn’t have one.

forEachBlock

Reads file by byte blocks and calls action for each block read. Block has default size which is implementation-dependent. This functions passes the byte array and amount of bytes in the array to the action function.

Reads file by byte blocks and calls action for each block read. This functions passes the byte array and amount of bytes in the array to the action function.

fun File . forEachBlock (
blockSize : Int ,
action : ( buffer : ByteArray , bytesRead : Int ) -> Unit )

forEachLine

Reads this file line by line using the specified charset and calls action for each line. Default charset is UTF-8.

inputStream

Constructs a new FileInputStream of this file and returns it as a result.

invariantSeparatorsPath

Returns path of this File using the invariant separator ‘/’ to separate the names in the name sequence.

isRooted

Determines whether this file has a root or it represents a relative path.

nameWithoutExtension

Returns file’s name without an extension.

normalize

Removes all . and resolves all possible .. in this file name. For instance, File(«/foo/./bar/gav/../baaz»).normalize() is File(«/foo/bar/baaz») .

outputStream

Constructs a new FileOutputStream of this file and returns it as a result.

printWriter

Returns a new PrintWriter for writing the content of this file.

readBytes

Gets the entire content of this file as a byte array.

reader

Returns a new FileReader for reading the content of this file.

readLines

Reads the file content as a list of lines.

readText

Gets the entire content of this file as a String using UTF-8 or specified charset.

relativeTo

Calculates the relative path for this file from base file. Note that the base file is treated as a directory. If this file matches the base file, then a File with empty path will be returned.

relativeToOrNull

Calculates the relative path for this file from base file. Note that the base file is treated as a directory. If this file matches the base file, then a File with empty path will be returned.

relativeToOrSelf

Calculates the relative path for this file from base file. Note that the base file is treated as a directory. If this file matches the base file, then a File with empty path will be returned.

resolve

Adds relative file to this, considering this as a directory. If relative has a root, relative is returned back. For instance, File(«/foo/bar»).resolve(File(«gav»)) is File(«/foo/bar/gav») . This function is complementary with relativeTo, so f.resolve(g.relativeTo(f)) == g should be always true except for different roots case.

Adds relative name to this, considering this as a directory. If relative has a root, relative is returned back. For instance, File(«/foo/bar»).resolve(«gav») is File(«/foo/bar/gav») .

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