FileOutputStream Class in Java

In this article, we'll dive deep into understanding and effectively using the FileOutputStream class in Java.

1. Introduction to FileOutputStream 

FileOutputStream creates an OutputStream that you can use to write bytes to a file. This class is ideal for writing byte-oriented data, such as binary files, though it can be used for text files as well. 

2. Getting Started with FileOutputStream 

Basic Usage: 

Creating an instance of FileOutputStream is straightforward. You can initialize it with either a filename or a File object.

FileOutputStream fos = new FileOutputStream("output.txt");

Writing Bytes: 

To write bytes to a file, you can use the write() method.

fos.write(65);  // Writes the byte 'A' to the file

Writing Arrays of Bytes: 

To write larger data or chunks of bytes, you can utilize byte arrays.

byte[] data = {65, 66, 67};
fos.write(data);  // Writes 'ABC' to the file

3. Handling Exceptions 

File I/O operations are prone to errors. The main exception you'll encounter with FileOutputStream is IOException.

try (FileOutputStream fos = new FileOutputStream("output.txt")) {
    // write data
} catch (IOException e) {

The try-with-resources statement ensures the stream closes automatically, promoting best practices and preventing potential resource leaks. 

4. Advantages of FileOutputStream 

Flexibility: Works seamlessly with both binary and text data. 

Performance: Delivers efficient write operations, especially when used with buffering. 

5. When to Use FileOutputStream?

Writing Binary Data: Opt for FileOutputStream when you need to write raw binary data to a file, such as saving images, audio files, or any other non-textual data. 

Direct File Interactions: When you need a straightforward mechanism to write data byte-by-byte to a file without any buffering or character conversion, FileOutputStream is the go-to choice. 

Stream Chaining & Processing: FileOutputStream is essential when you need a byte-based stream as the destination in stream chaining or processing, such as when using BufferedOutputStream or CipherOutputStream for encryption. 

Note: For writing character data with potential encoding considerations, it's often better to use character-based streams like FileWriter.

6. Enhancing FileOutputStream with BufferedOutputStream 

For even faster write operations, you can wrap a FileOutputStream with a BufferedOutputStream. This approach provides additional buffering.

try (BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("output.txt"))) {
    // write bytes
} catch (IOException e) {

7. Complete Code

Let's combine all the steps into a single FileOutputStreamExample class. 
This class will: 
  • Create a FileOutputStream object. 
  • Write bytes using both methods (single byte and array of bytes). 
  • Handle exceptions. 
  • Enhance FileOutputStream with BufferedOutputStream.

public class FileOutputStreamExample {

    public static void main(String[] args) {
        String filePath = "output.txt";
        // Step 2: Basic Usage
        try (FileOutputStream fos = new FileOutputStream(filePath)) {
            // Writing Single Byte
            fos.write(65);  // Writes the byte 'A' to the file
            System.out.println("Wrote single byte 'A' to the file.");

            // Writing Arrays of Bytes
            byte[] data = {66, 67, 68};
            fos.write(data);  // Writes 'BCD' to the file
            System.out.println("Wrote byte array 'BCD' to the file.");
        } catch (IOException e) {
            System.out.println("Error writing to the file: " + e.getMessage());

        // Step 6: Enhancing FileOutputStream with BufferedOutputStream
        try (BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(filePath, true))) {
            byte[] moreData = {69, 70, 71};  // 'EFG'
            System.out.println("Appended byte array 'EFG' to the file using BufferedOutputStream.");
        } catch (IOException e) {
            System.out.println("Error writing to the file using BufferedOutputStream: " + e.getMessage());

// Sample Output:
// Wrote single byte 'A' to the file.
// Wrote byte array 'BCD' to the file.
// Appended byte array 'EFG' to the file using BufferedOutputStream.

Related Java I/O Classes