File to byte

java

file-io

memory-management

apache-commons

byNikita Barsukov·Aug 3, 2024

Effortlessly convert a File to a byte[] in Java using this snippet:

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;

public static byte[] fileToByteArray(String filePath) throws IOException {
    return Files.readAllBytes(Path.of(filePath));
}

Use Files.readAllBytes() - the Swiss Army knife - that adroitly handles both the file reading and the byte array conversion. A Picasso painting for small files; for larger files, consider dipping your toes into Java NIO with FileChannel to optimize memory usage and performance.

Got a large file that's bugging you? Stream it piece by piece with:

import java.io.InputStream;
import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.IOException;

public static byte[] largeFileToByteArray(String filePath) throws IOException {
    try (InputStream input = new FileInputStream(filePath);
         ByteArrayOutputStream output = new ByteArrayOutputStream()) {
        byte[] buffer = new byte[1024];
        int bytesRead;
        while ((bytesRead = input.read(buffer)) != -1) {
            output.write(buffer, 0, bytesRead); // goodbye OutOfMemoryError
        }
        return output.toByteArray(); // clone() not required 😎
    }
}

Here we read chunks of data iteratively, leaving the elephant out of the room - loading the entire file in memory.

Handling various file sizes and edge cases

Tackling Godzilla-sized files

Need to process a Mammoth-sized file? Here are your shields and swords:

import java.io.*;
import java.nio.*;
import java.nio.channels.*;

public static byte[] memoryMappedFileToByteArray(String filePath) throws IOException {
    try (FileChannel fileChannel = new RandomAccessFile(filePath, "r").getChannel()) {
        MappedByteBuffer buffer = fileChannel.map(FileChannel.MapMode.READ_ONLY, 0, fileChannel.size());
        if (buffer.remaining() > Integer.MAX_VALUE) {
            throw new IOException("File is sure bigger than my future");
        }
        byte[] bytes = new byte[buffer.remaining()];
        buffer.get(bytes);
        return bytes;
    }
}

Securing I/O operations

Make sure your I/O streams are safely tucked in bed using a finally block or try-with-resources:

try(InputStream inputStream = new FileInputStream(filePath)) {
    // Byte wrangling here
} // The inputStream will be closed, come hail or high water.

Keeping file size in check

Impose a file size limit to keep memory issues at bay.

Utilizing third-party libraries for advanced conversions

Streamlining with Apache Commons IO

Apache Commons FileUtils - a hacker's multi-tool:

import org.apache.commons.io.FileUtils;
import java.io.File;
import java.io.IOException;

public static byte[] convertFileToByteArrayWithCommonsIo(File file) throws IOException {
    return FileUtils.readFileToByteArray(file); // One-liners for the win!
}

Dealing with edge cases and different methodologies

Maintaining the watch for `read()`

During file reading, always keep an eye for a -1 return value from read() operation:

while ((bytesRead = inputStream.read(buffer)) != -1) {
}

This puts a lid on making sure we have read the entire file.

Full control with RandomAccessFile

Use RandomAccessFile combined with RandomAccessFile#readFully(byte[]) for those times when you need the steering and clutch in your hands:

RandomAccessFile file = new RandomAccessFile("data.bin", "r");
byte[] bytes = new byte[(int) file.length()];
file.readFully(bytes);

Identifying when not to use `Files.readAllBytes()`

Resist the urge to utilize it when:

Engaging with large files, you wouldn’t want OutOfMemoryError to spoil the party.
Your idea of fun is incremental processing of file data.

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