Java Read a text file line by line

摘要: This article covers 3 ways to read a text file line by line :

This article covers 3 ways to read a text file line by line :

Java NIO libraries – FileChannel to read the files. It is a non-blocking mode of reading files
BufferedReader – Which is a blocking operation i.e it blocks any other read/write request to the file until it has completed the task.
Apache Commons IO – FileUtils, simpler way to read files line by line. It is also a blocking operation.

The input file for each example is same as the one shown below:

src/com/mkyong/data.txt

1. Java NIO libraries

The example presents the simplest way of reading a small file. Since this is a small file, we directly allocate required memory to ByteBuffer using FileChannel size.

NIOFileReadExample.java

package com.mkyong;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class NIOFileReadExample {
    public static void main(String[] args) throws IOException {
        RandomAccessFile file = new RandomAccessFile("src/com/mkyong/data.txt", "r");
        FileChannel channel = file.getChannel();
        System.out.println("File size is: " + channel.size());
        ByteBuffer buffer = ByteBuffer.allocate((int) channel.size());
        channel.read(buffer);
        buffer.flip();//Restore buffer to position 0 to read it
        System.out.println("Reading content and printing ... ");
        for (int i = 0; i < channel.size(); i++) {
            System.out.print((char) buffer.get());
        channel.close();
        file.close();

On executing the code you get the below output:

File size is: 19
Reading content and printing ...

2. BufferedReader

ReadTextFile.java

package com.mkyong;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
public class ReadTextFile {
    public static void main(String[] args) throws IOException {
        try {
            File f = new File("src/com/mkyong/data.txt");
            BufferedReader b = new BufferedReader(new FileReader(f));
            String readLine = "";
            System.out.println("Reading file using Buffered Reader");
            while ((readLine = b.readLine()) != null) {
                System.out.println(readLine);
        } catch (IOException e) {
            e.printStackTrace();

The output on executing this code will be as shown below:

Reading file using Buffered Reader

Note
More BufferedReader examples

3. Apache Commons IO

pom.xml

  <dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.5</version>
  </dependency>

FileIOUtilsExample

package com.mkyong;
import org.apache.commons.io.FileUtils;
import java.io.File;
import java.io.IOException;
import java.util.List;
public class ReadTextFile {
    public static void main(String[] args) throws IOException {
        try {
            File f = new File("src/com/mkyong/data.txt");
            System.out.println("Reading files using Apache IO:");
            List<String> lines = FileUtils.readLines(f, "UTF-8");
            for (String line : lines) {
                System.out.println(line);
        } catch (IOException e) {
            e.printStackTrace();

The output on executing above code will be: