Java - ObjectOutputStream write(byte[] buf) method

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Description

The Java ObjectOutputStream write(byte[] buf) method writes an array of bytes. This method will block until the bytes are actually written.

Declaration

Following is the declaration for java.io.ObjectOutputStream.write(byte[] buf) method.

 public void write(byte[] buf) 

Parameters

buf − The data to be written.

Return Value

This method does not return a value.

Exception

• IOException − If I/O errors occur.

Example - Usage of ObjectOutputStream write(byte[] buf) method

The following example shows the usage of ObjectOutputStream write(byte[] buf) method.

ObjectOutputStreamDemo.java

 package com.tutorialspoint; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; public class ObjectOutputStreamDemo { public static void main(String[] args) { byte b = 'a'; try { // create a new file with an ObjectOutputStream FileOutputStream out = new FileOutputStream("test.txt"); ObjectOutputStream oout = new ObjectOutputStream(out); // write something in the file oout.write(b); // close the stream oout.close(); // create an ObjectInputStream for the file we created before ObjectInputStream ois = new ObjectInputStream(new FileInputStream("test.txt")); // read and print a string System.out.println("" + (char) ois.readByte()); } catch (Exception ex) { ex.printStackTrace(); } } } 

Output

Let us compile and run the above program, this will produce the following result −

 a 

Example - Write raw byte array data to a file using ObjectOutputStream

The following example shows the usage of ObjectOutputStream write(byte[] buf) method.

ObjectOutputStreamDemo.java

 package com.tutorialspoint; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; public class ObjectOutputStreamDemo { public static void main(String[] args) throws IOException { byte[] data = "Hello, byte stream!".getBytes(); FileOutputStream fos = new FileOutputStream("raw_bytes1.bin"); fos.write(data); // Write raw byte array System.out.println("Byte array written to file."); FileInputStream fis = new FileInputStream("raw_bytes1.bin"); byte[] dat = fis.readAllBytes(); String content = new String(dat); System.out.println("Content after skipping header: " + content); } } 

Output

Let us compile and run the above program, this will produce the following result−

 Byte array written to file. Content after skipping header: Hello, byte stream! 

Explanation

• The byte array is written directly to the file.

• This is not serialized as an object, just raw binary data.

• You could read it back using a FileInputStream.

Example - Write a byte array followed by a serialized object

The following example shows the usage of ObjectOutputStream write(byte[] buf) method. We're combining low-level byte writing and object serialization in the same stream.

ObjectOutputStreamDemo.java

 package com.tutorialspoint; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; public class ObjectOutputStreamDemo { public static void main(String[] args) { byte[] header = {0x01, 0x02, 0x03}; // custom header before object data try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("mixed_data.bin"))) { oos.write(header); // write raw bytes (e.g. versioning info) oos.flush(); // write a serializable object afterward oos.writeObject(new Message("Hello from serialized object!")); System.out.println("Header and object written to file."); } catch (IOException e) { e.printStackTrace(); } } static class Message implements Serializable { private static final long serialVersionUID = 1L; String content; public Message(String content) { this.content = content; } } } 

Output

Let us compile and run the above program, this will produce the following result−

 Header and object written to file. 

Explanation

• The stream starts with raw bytes (you could use them as a custom protocol header).

• Then it writes a serialized Java object.

• On deserialization, you'd read the header with InputStream.read() before calling readObject().