Java - ObjectInputStream read() method

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Description

The Java ObjectInputStream read() method reads a single byte or an array of bytes from the input stream. It is used for reading raw byte data rather than deserializing objects.

Declaration

Following is the declaration for java.io.ObjectInputStream.read() method −

public int read()

Parameters

NA

Return Value

This method returns the byte read, or -1 if the end of the stream is reached.

Exception

IOException − If an I/O error has occurred.

Example - Usage of ObjectInputStream read() method

The following example shows the usage of Java ObjectInputStream read() method.

ObjectInputStreamDemo.java

package com.tutorialspoint;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class ObjectInputStreamDemo {
   public static void main(String[] args) {
      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.writeUTF("Hello World");
         oout.flush();

         // create an ObjectInputStream for the file we created before
         ObjectInputStream ois = new ObjectInputStream(new FileInputStream("test.txt"));

         // read from the stream
         for (int i = 0; i < ois.available();) {
            System.out.print("" + (char) ois.read());
         }
      } catch (Exception ex) {
         ex.printStackTrace();
      }
   }
}

Output

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

Hello World

Example - Reading One Byte at a Time

The following example shows the usage of Java ObjectInputStream read() method. This example writes raw bytes to a file and then reads them one byte at a time using ObjectInputStream.read().

ObjectInputStreamDemo.java

package com.tutorialspoint;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class ObjectInputStreamDemo {
   public static void main(String[] args) {
      try {
         // Writing raw bytes to a file
         FileOutputStream fos = new FileOutputStream("data.dat");
         ObjectOutputStream oos = new ObjectOutputStream(fos);
         oos.write(65); // Writing 'A' (ASCII 65)
         oos.write(66); // Writing 'B' (ASCII 66)
         oos.write(67); // Writing 'C' (ASCII 67)
         oos.close();

         // Reading bytes using ObjectInputStream
         FileInputStream fis = new FileInputStream("data.dat");
         ObjectInputStream ois = new ObjectInputStream(fis);

         int byteRead;
         while ((byteRead = ois.read()) != -1) { // Read until end of stream
            System.out.println("Read byte: " + byteRead + " (" + (char) byteRead + ")");
         }

         ois.close();
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

Read byte: 65 (A)
Read byte: 66 (B)
Read byte: 67 (C)

Explanation

• Writes raw bytes (65, 66, 67) to a file (data.dat).

• Reads bytes one by one using read() until EOF (-1) is reached.

• Each byte is printed as its ASCII character.

Example - Reading Multiple Bytes into a Byte Array

The following example shows the usage of Java ObjectInputStream read() method. This example writes an array of bytes and reads them using read(byte[] b, int off, int len).

ObjectInputStreamDemo.java

package com.tutorialspoint;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class ObjectInputStreamDemo {
   public static void main(String[] args) {
      try {
         // Writing byte array to a file
         FileOutputStream fos = new FileOutputStream("data.bin");
         ObjectOutputStream oos = new ObjectOutputStream(fos);
         oos.write(new byte[]{72, 101, 108, 108, 111}); // "Hello"
         oos.close();

         // Reading bytes using ObjectInputStream
         FileInputStream fis = new FileInputStream("data.bin");
         ObjectInputStream ois = new ObjectInputStream(fis);

         byte[] buffer = new byte[5]; // Buffer to hold 5 bytes
         int bytesRead = ois.read(buffer, 0, buffer.length);

         System.out.println("Bytes Read: " + bytesRead);
         System.out.println("Read String: " + new String(buffer));

         ois.close();
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

Bytes Read: 5
Read String: Hello

Explanation

• Writes the byte array {72, 101, 108, 108, 111} ("Hello") to a file.

• Uses read(byte[] b, int off, int len) to read 5 bytes into a buffer.

• Converts the byte array to a string and prints "Hello".