Java Read Files – Efficient File Reading in Java

Introduction – Why File Reading Matters

Reading data from files is a critical part of many Java applications—whether it’s loading configuration settings, importing datasets, or reading logs. Java provides a variety of APIs to read files, from traditional methods like FileReader to modern approaches like Files.readAllLines().

In this guide, you’ll learn:

• How to read files in Java using different techniques
• When to use FileReader, BufferedReader, Scanner, or Files
• How to handle exceptions and resources safely
• Performance tips and best practices for large file reading

Java File Reading Classes

Read File Using FileReader

import java.io.FileReader;
import java.io.IOException;

public class FileReaderExample {
    public static void main(String[] args) {
        try (FileReader reader = new FileReader("example.txt")) {
            int character;
            while ((character = reader.read()) != -1) {
                System.out.print((char) character);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Explanation:

• Reads character-by-character
• Suitable for small text files
• Uses try-with-resources to auto-close

Read File Using BufferedReader

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class BufferedReaderExample {
    public static void main(String[] args) {
        try (BufferedReader br = new BufferedReader(new FileReader("example.txt"))) {
            String line;
            while ((line = br.readLine()) != null) {
                System.out.println(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Explanation:

• Efficient for line-by-line reading
• Avoids character-by-character I/O bottlenecks
• Ideal for reading logs or text files line-by-line

Read File Using Scanner

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class ScannerExample {
    public static void main(String[] args) {
        try (Scanner scanner = new Scanner(new File("example.txt"))) {
            while (scanner.hasNextLine()) {
                System.out.println(scanner.nextLine());
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }
}

Explanation:

• Great for parsing numbers, words, tokens
• Use .hasNext(), .nextInt(), .nextDouble() etc.
• More flexible for structured file content

Read All Lines Using Files.readAllLines()

import java.nio.file.*;
import java.io.IOException;
import java.util.List;

public class FilesReadAllLinesExample {
    public static void main(String[] args) throws IOException {
        List<String> lines = Files.readAllLines(Paths.get("example.txt"));
        lines.forEach(System.out::println);
    }
}

Explanation:

• Reads all lines into a List<String>
• Simple and modern, but loads entire file into memory
• Suitable for small to medium files

Stream-based Reading Using Files.lines()

Files.lines(Paths.get("example.txt"))
     .filter(line -> !line.isEmpty())
     .forEach(System.out::println);

Explanation:

• Returns a Stream of lines for efficient, lazy processing
• Can filter, map, reduce during reading

Tip: Always close streams or use try-with-resources.

Comparison Table

Best Practices

• Use BufferedReader or Files.lines() for large files
• Always use try-with-resources to auto-close readers
• Avoid readAllLines() on large files — memory overload
• Prefer Files API for modern Java apps
• Handle IOException and FileNotFoundException properly

Summary – Java File Reading Techniques

Java offers flexible file reading methods for different scenarios — whether you need line-by-line efficiency, token-based parsing, or modern stream processing.

Key Takeaways:

• Use FileReader and BufferedReader for traditional reading
• Use Scanner for parsing structured text
• Use Files.readAllLines() for simplicity (small files)
• Use Files.lines() for memory-efficient streaming
• Apply try-with-resources and exception handling always

FAQs – Java Read Files

What is the easiest way to read a file in Java?

Use Files.readAllLines() for small files or Files.lines() for large files with stream processing.

How to read a file line-by-line in Java?

Use BufferedReader.readLine() inside a loop or Scanner.nextLine().

Which is better: BufferedReader or Scanner?

Use BufferedReader for performance, and Scanner for parsing tokens like integers or words.

How to avoid memory issues with large files?

Use Files.lines() or BufferedReader, which read line-by-line instead of loading entire content at once.

Can I read files with UTF-8 encoding?

Yes, use new InputStreamReader(new FileInputStream("file.txt"), StandardCharsets.UTF_8) or specify charset in Files.newBufferedReader().