Sentry Answers>Java>

Read a plain text file in Java

Read a plain text file in Java

David Y.

—

The Problem

What is the best way to read a plain text file in modern Java?

The Solution

To read the entire contents of a file into a single String variable, you can use the Files.readString method. The method was introduced in Java 11 and is a good way of handling small files. For example, the code below reads the text of myfile.txt and prints it:

Click to Copy
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.io.IOException;

public class ReadFile {
    public static void main(String[] args) {
        Path filePath = Paths.get("myfile.txt");
        try {
            String content = Files.readString(filePath);
            System.out.println(content); // print entire file content
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

For larger files, or files where we want to process each line separately rather than reading the whole thing in at once, you can use Files.lines, which was introduced in Java 8. It returns a Stream<String> object. Here’s another version of the file-reading code:

Click to Copy
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.io.IOException;
import java.util.stream.Stream;

public class ReadFile {
    public static void main(String[] args) {
        Path filePath = Paths.get("myfile.txt");
        try (Stream<String> lines = Files.lines(filePath)) {
            lines.forEach(System.out::println); // print each line
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Code written in older versions of Java will often use a BufferedReader and a FileReader to read files. This class has been available since Java 1.1 and offers more control over how the file is read. For example, you can use the read and skip methods to read four characters from the start of the file, skip the next six characters, and then read another five characters. You can also read the file line by line, as we did above with File.lines. For example:

Click to Copy
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

public class ReadFile {
    public static void main(String[] args) throws FileNotFoundException { // must throw FileNotFoundException when using FileReader

        String path = "myfile.txt";
        BufferedReader reader = new BufferedReader(new FileReader(path));
        try {
            String line;
            while ((line = reader.readLine()) != null) {
                System.out.println(line); // print each line until the end of the file
            }
        } catch (IOException e) {
            e.printStackTrace(); // print error if file reading fails
        } finally {
            try {
                if (reader != null) { // close the BufferedReader and free the memory it used
                    reader.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

When writing modern Java, the first two methods should be preferred. The BufferedReader method will be encountered in older codebases and can still be used when necessary for either backward compatibility or increased control over the file reading process.

  • Sentry BlogException Handling in Java (with Real Examples)
  • Syntax.fmListen to the Syntax Podcast
  • Syntax.fm logo
    Listen to the Syntax Podcast

    Tasty treats for web developers brought to you by Sentry. Get tips and tricks from Wes Bos and Scott Tolinski.

    SEE EPISODES

Considered “not bad” by 4 million developers and more than 100,000 organizations worldwide, Sentry provides code-level observability to many of the world’s best-known companies like Disney, Peloton, Cloudflare, Eventbrite, Slack, Supercell, and Rockstar Games. Each month we process billions of exceptions from the most popular products on the internet.

learn more about sentryjoin our discord
© 2024 • Sentry is a registered Trademark of Functional Software, Inc.