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 copy a file in JDK 7?

In this example you’ll see how to copy a file using the new API provided in the JDK 7. The first step is to define the source and the target of the file to be copied. For this we can use the Path class. To create an instance of Path we use the Paths.get() method by passing the path information as the arguments.

Next we can configure the file copy operation option. For this we can define it as an array of CopyOtion. We can use copy option such as StandardCopyOption.REPLACE_EXISTING and StandardCopyOption.COPY_ATTRIBUTES.

Finally to copy the file we use the Files.copy() method. We give three arguments to this method, they are the source file, the target file and the copy options information.

Let’s see the code snippet below:


import java.nio.file.*;

public class NioFileCopyDemo {
    public static void main(String[] args) {
        // Define the source and target of the file to be copied.
        Path source = Paths.get("C:/resources/data.txt");
        Path target = Paths.get("C:/resources/data.bak");

        // Define the options used in the file copy process.
        CopyOption[] options = new CopyOption[] {

        try {
            // Copy file from source to target using the defined 
            // configuration.
            Files.copy(source, target, options);
        } catch (IOException e) {