How to read text file contents line by line?

In the following code example you will learn how to read file contents line by line using the Apache Commons FileUtils.lineIterator() method. Reading file contents one line at a time, do some processing, and release it from memory immediately will lower the memory consumption used by your program.

The snippet below give you the basic usage of the FileUtils.lineIterator() method. You pass the file to read and the encoding to use. An Iterator of the lines in the file will be returned. Use the hasNext() method to see if there are lines to read from the iterator. The nextLine() method will give you the next line from the file.

When we finished with the iterator we need to close it using the LineIterator.close() or LineIterator.closeQuietly() method.



import java.util.Objects;

public class ReadFileLineByLine {
    public static void main(String[] args) throws Exception {
        // Load file from resource directory.
        ClassLoader classLoader = ReadFileLineByLine.class.getClassLoader();
        URL url = Objects.requireNonNull(classLoader.getResource("data.txt"),
                "Resource could not be found.");

        File file = new File(url.getFile());
        LineIterator iterator = FileUtils.lineIterator(file, "UTF-8");
        try {
            while (iterator.hasNext()) {
                String line = iterator.nextLine();
                System.out.println("line = " + line);
        } finally {

In the example above we load the file from a resource directory. That’s why we use the ClassLoader.getResource() method. If you want to load a file from an absolute path you can simply create a File object and pass the absolute path to the file.

Maven Dependency


How do I find files in a directory using DirectoryStream?

In this example we are going to learn to use the DirectoryStream, which part of java.nio.file package, to find files in a directory. We are begin by creating a Path, the directory where the search will be conducted.

After that we create a DirectoryStream using Files.newDirectoryStream(). To create a directory stream we passed two arguments, the starting path and a glob expression. Below we use *.txt glob expression to filter all text files in the D:/Workbench.

To get all the entries of the directory stream we can use a foreach loop as can be seen below. We iterate each entries, which is a Path object. And we print the entries file name using the getFileName() method.


import java.nio.file.DirectoryStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

public class FindFilesInDirectory {
    public static void main(String[] args) {
        Path dir = Paths.get("D:/Workbench");

        try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir, "*.txt")) {
            for (Path entry : stream) {
        } catch (IOException e) {

You can also notice that in this example we are using the try-with-resource statement. This mean that the DirectoryStream will be closed appropriately when the process is done. This type of try statement is an improvement introduced in JDK 7.