Java FileReader tutorial

last modified July 6, 2020

Java FileReader tutorial shows how to use FileReader class to read text files in Java.

Java tutorial is a comprehensive tutorial on Java language.

The examples use this text file:

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. 

Java FileReader

FileReader is a Java convenience class for reading text data to files. FileReader extends InputStreamReader and creates the FileInputStream.

Java FileReader example

In the following example, we use FileReader to read a text file.

package com.zetcode;

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

public class FileReaderEx {

    public static void main(String[] args) throws IOException {

        var fileName = "src/resources/thermopylae.txt";
        char[] buf = new char[1024];

        try (var fr = new FileReader(fileName, StandardCharsets.UTF_8)) {

            int c;
            while ((c = fr.read(buf)) != -1) {

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

The example reads a text file. It uses a character buffer to improve the performance of the operation.

try (var fr = new FileReader(fileName, StandardCharsets.UTF_8)) {

The first argument of the FileReader is the file name. The second is the encoding type. We use try-with-resources construct to clean resources after we have finished writing.

int c;
while ((c = fr.read(buf)) != -1) {

    System.out.println(buf);
}

The FileReader's read() method reads characters into an array. It returns the the number of characters read, or -1 if the end of the stream has been reached.

Java FileReader with BufferedReader

FileReader's performance can be improved with BufferedReader. BufferedReader reads text from a character-input stream, buffering characters so as to provide for the efficient reading of characters, arrays, and lines. The buffer size may be specified, or the default size may be accepted; the default is large enough for most purposes.

package com.zetcode;

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

public class JavaFileReaderBuffered {

    public static void main(String[] args) throws IOException {

        var fileName = "src/resources/thermopylae.txt";
        
        try (var br = new BufferedReader(new FileReader(fileName, StandardCharsets.UTF_8))) {

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

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

In the example, we wrap the FileReader into the BufferedReader to improve its performance.

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

    System.out.println(line);
}

The readLine() reads a line of text. It returns the string containing the contents of the line, not including any line-termination characters, or null if the end of the stream has been reached without reading any characters.

In this tutorial, we have presented the Java FileReader class.

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