How to Read File in Java: Simple Syntax and Example

To read a file in Java, you can use BufferedReader with FileReader or the Files.readAllLines() method. These methods let you open a file and read its contents line by line or all at once.

Syntax

Here are two common ways to read a file in Java:

• BufferedReader with FileReader: Reads the file line by line.
• Files.readAllLines: Reads all lines into a list at once.

Each method requires specifying the file path.

java

import java.io.BufferedReader;
import java.io.FileReader;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.List;

try (BufferedReader reader = new BufferedReader(new FileReader("path/to/file.txt"))) {
    String line;
    while ((line = reader.readLine()) != null) {
        // process line
    }
}

// Or using Files API
List<String> lines = Files.readAllLines(Paths.get("path/to/file.txt"));

Example

This example reads a file named example.txt line by line and prints each line to the console.

java

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

public class ReadFileExample {
    public static void main(String[] args) {
        String filePath = "example.txt";
        try (BufferedReader reader = new BufferedReader(new FileReader(filePath))) {
            String line;
            while ((line = reader.readLine()) != null) {
                System.out.println(line);
            }
        } catch (IOException e) {
            System.err.println("Error reading file: " + e.getMessage());
        }
    }
}

Output

Hello, this is line 1.
This is line 2.
End of file.

Common Pitfalls

Common mistakes when reading files in Java include:

• Not closing the file, which can cause resource leaks. Use try-with-resources to close automatically.
• Using incorrect file paths, leading to FileNotFoundException.
• Not handling IOException, which can crash the program.

java

/* Wrong way: Not closing the reader */
BufferedReader reader = new BufferedReader(new FileReader("file.txt"));
String line = reader.readLine();
// reader.close() is missing

/* Right way: Using try-with-resources */
try (BufferedReader reader = new BufferedReader(new FileReader("file.txt"))) {
    String line = reader.readLine();
} catch (IOException e) {
    e.printStackTrace();
}

Quick Reference

Summary tips for reading files in Java:

• Use try-with-resources to auto-close files.
• Choose BufferedReader for line-by-line reading.
• Use Files.readAllLines() for small files to read all lines at once.
• Always handle IOException.

Key Takeaways

Use try-with-resources to automatically close files after reading.

BufferedReader with FileReader reads files line by line efficiently.

Files.readAllLines() reads all lines into a list for small files.

Always handle IOException to avoid program crashes.

Check your file path carefully to prevent FileNotFoundException.