Reading text files in Java

last modified July 10, 2024

In Reading text files in Java tutorial we show how to read text files in Java. We use build-in tools including FileReader, InputStreamReader, and Scanner.

The following examples use this text file.

src/main/resources/thermopylae.txt

The Battle of Thermopylae was fought between an alliance of Greek city-states, 
led by King Leonidas of Sparta, and the Persian Empire of Xerxes I over the 
course of three days, during the second Persian invasion of Greece.

The file is located in the src/main/resources/ directory.

Java read text classes

We can use the following Java classes to read text files in Java.

java.io.FileReader
java.nio.file.Files
java.util.Scanner
java.io.InputStreamReader
com.google.common.io.Files

Read text file with FileReader

FileReader is a class used for reading character files. It reads text from character files using a default buffer size. Decoding from bytes to characters uses either a specified charset or the platform's default charset.

Note: In the past, FileReader relied on the default platform's encoding. Since Java 11, the issue was corrected. It is possible now to explicitly specify the encoding.

Main.java

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.nio.charset.StandardCharsets;

void main() throws IOException {

    var fileName = "src/main/resources/thermopylae.txt";

    try (BufferedReader br = new BufferedReader(
            new FileReader(fileName, StandardCharsets.UTF_8))) {

        var sb = new StringBuilder();

        String line;
        while ((line = br.readLine()) != null) {

            sb.append(line);
            sb.append(System.lineSeparator());
        }

        System.out.println(sb);
    }
}

The code example reads text from the thermopylae.txt file.

var fileName = "src/main/resources/thermopylae.txt";

In the fileName variable, we store the path to the file.

try (BufferedReader br = new BufferedReader(
    new FileReader(fileName, StandardCharsets.UTF_8))) {

The FileReader takes the file name as the first parameter. The second parameter is the charset used. The FileReader is passed to the BufferedReader, which buffers read operations for better performance. This is a try-with-resources statement which ensures that the resource (the buffered reader) is closed at the end of the statement.

var sb = new StringBuilder();

String line;
while ((line = br.readLine()) != null) {

    sb.append(line);
    sb.append(System.lineSeparator());
}

System.out.println(sb);

Printing lines to the console consumes additional resources. Therefore, we use the StringBuilder to build the output string and print it in one operation. This is an optional optimization. The System.lineSeparator returns the system-dependent line separator string.

Read text file with Files.readAllLines

The Files.readAllLines method reads all lines from a file. This method ensures that the file is closed when all bytes have been read or an exception is thrown. The bytes from the file are decoded into characters using the specified charset.

Note that this method reads the whole file into the memory; therefore, it may not be suitable for very large files.

Main.java

import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.List;

void main() throws IOException {

    var fileName = "src/main/resources/thermopylae.txt";

    List<String> lines = Files.readAllLines(Paths.get(fileName),
            StandardCharsets.UTF_8);

    for (String line : lines) {

        System.out.println(line);
    }
}

The contents of the thermopylae.txt file are read and printed to the console using the Files.readAllLines method.

Reading text file with streaming API

Another option to read text files is to use the Java streaming API. The Files.lines reads all lines from a file as a stream. The bytes from the file are decoded into characters using the StandardCharsets.UTF-8 charset.

Main.java

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.stream.Stream;

void main() throws IOException {

    var fileName = "src/main/resources/thermopylae.txt";

    var path = Paths.get(fileName);

    try (Stream<String> lines = Files.lines(path)) {
        lines.forEachOrdered(System.out::println);
    }
}

The contents of the thermopylae.txt file are read and printed to the console using the Files.lines method.

Read text file with Scanner

A Scanner is simple text scanner which can parse primitive types and strings using regular expressions.

Main.java

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

void main() throws FileNotFoundException {

    var fileName = "src/main/resources/thermopylae.txt";

    try (var scanner = new Scanner(new File(fileName))) {

        while (scanner.hasNext()) {

            String line = scanner.nextLine();
            System.out.println(line);
        }
    }
}

The example reads a text file using a Scanner.

while (scanner.hasNext()) {

    String line = scanner.nextLine();
    System.out.println(line);
}

The file is read line by line with the nextLine method.

Read text file with InputStreamReader

InputStreamReader is a bridge from byte streams to character streams. It reads bytes and decodes them into characters using a specified charset.

Main.java

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.nio.charset.StandardCharsets;

void main() throws IOException {

    var fileName = "src/main/resources/thermopylae.txt";

    try (var br = new BufferedReader(new InputStreamReader(
            new FileInputStream(fileName), StandardCharsets.UTF_8))) {

        String line;

        while ((line = br.readLine()) != null) {

            System.out.println(line);
        }
    }
}

The example reads a text file using an InputStreamReader.

try (var br = new BufferedReader(new InputStreamReader(
        new FileInputStream(fileName), StandardCharsets.UTF_8))) {

The InputStreamReader is created from a FileInputStream, which creates an input stream by opening a connection to an actual file. The InputStreamReader is then passed to a BufferedReader for better efficiency.

Java 7 introduced a more convenient API to work with an InputStreamReader. A new buffered InputStreamReader can be created with Files.newBufferedReader.

Main.java

import java.io.BufferedReader;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;

void main() throws IOException {

    var fileName = "src/main/resources/thermopylae.txt";
    var filePath = Paths.get(fileName);

    try (BufferedReader br = Files.newBufferedReader(
        filePath, StandardCharsets.UTF_8)) {

        String line;

        while ((line = br.readLine()) != null) {

            System.out.println(line);
        }
    }
}

The example reads the thermopylae.txt file with the Files.newBufferedReader method.

Read text file with Files.readAllBytes

The Files.readAllBytes method reads all the bytes from a file. It ensures that the file is closed when all bytes have been read.

Main.java

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;

void main() throws IOException {

    var fileName = "src/main/resources/thermopylae.txt";
    var filePath = Paths.get(fileName);

    byte[] data = Files.readAllBytes(filePath);
    var content = new String(data);

    System.out.println(content);
}

The example reads all bytes from a file and passes them to the String constructor.

Read text with Files.readString

Java 11 introduces a convenient method that allows to read the whole file into a string in one shot.

The Files.readString reads all content from a file into a string, decoding from bytes to characters using the specified or the default (StandardCharsets.UTF_8) charset. It ensures that the file is closed when all content have been read.

Main.java

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;

void main() throws IOException {

    var fileName = "src/main/resources/thermopylae.txt";
    var filePath = Paths.get(fileName);

    var content = Files.readString(filePath);

    System.out.println(content);
}

The example reads the contents of the thermopylae.txt file into a string a prints it to the terminal.

Read text file with FileChannel

FileChannel is a channel for reading, writing, mapping, and manipulating a file. The advantages of file channels include reading and writing at a specific position of a file, loading a section of a file, or locking a section of a file.

Main.java

import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

void main() throws IOException {

    var fileName = "src/main/resources/thermopylae.txt";

    try (RandomAccessFile myFile = new RandomAccessFile(fileName, "rw");
            FileChannel inChannel = myFile.getChannel()) {

        ByteBuffer buf = ByteBuffer.allocate(48);

        int bytesRead = inChannel.read(buf);

        while (bytesRead != -1) {

            buf.flip();

            while (buf.hasRemaining()) {

                System.out.print((char) buf.get());
            }

            buf.clear();
            bytesRead = inChannel.read(buf);
        }
    }
}

The example reads the text file with FileChannel.

try (RandomAccessFile myFile = new RandomAccessFile(fileName, "rw");
        FileChannel inChannel = myFile.getChannel()) {

A FileChannle is created from a RandomAccessFile.

ByteBuffer buf = ByteBuffer.allocate(48);

int bytesRead = inChannel.read(buf);

We allocate a buffer and read initial data.

while (bytesRead != -1) {

    buf.flip();

    while (buf.hasRemaining()) {

        System.out.print((char) buf.get());
    }

    buf.clear();
    bytesRead = inChannel.read(buf);
}

We read the data into the buffer and write it to the terminal. We use flip to change buffer from reading to writing.

Source

Java Basic I/O

In this article we have read text files in various ways in Java.

Author

My name is Jan Bodnar and I am a passionate programmer with many years of programming experience. I have been writing programming articles since 2007. So far, I have written over 1400 articles and 8 e-books. I have over eight years of experience in teaching programming.

List all Java tutorials.

Ebooks

Reading text files in Java

Java read text classes

Read text file with FileReader

Read text file with Files.readAllLines

Reading text file with streaming API

Read text file with Scanner

Read text file with InputStreamReader

Read text file with Files.readAllBytes

Read text with Files.readString

Read text file with FileChannel

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