Java ObjectInputStream Class

August 4, 2023

What is Java ObjectInputStream Class?

Java ObjectInputStream class is a class that is used to deserialize Java objects from an input stream.It is commonly used in client-server applications and in file handling.

It is a part of the Java IO package and is used to read Java objects that have been previously serialized. ObjectInputStream reads the serialized objects and reconstructs them into their original state.

To understand the Java ObjectInputStream, Read the Complete Article.

Working of ObjectInputStream

Here’s how ObjectInputStream works:
- ObjectInputStream reads a stream of bytes from an input source, such as a file or a network socket.
- The stream of bytes must contain data that was previously serialized using ObjectOutputStream.
- ObjectInputStream uses a combination of reflection and metadata embedded in the serialized data to reconstruct the original object.
- As it reads the serialized data, ObjectInputStream checks the class hierarchy to ensure that the serialized data matches the expected type.
- ObjectInputStream also performs some security checks to prevent malicious code from being executed during deserialization.
- Once the deserialization process is complete, the reconstructed object can be used just like any other Java object.
- It is important to note that the deserialization process can be resource-intensive, especially for large or complex objects. Therefore, it is important to use ObjectInputStream judiciously and to avoid deserializing untrusted data.

Create an ObjectInputStream

How to create an ObjectInputStream in Java:

First, open an input stream from a data source, such as a file or a network socket.
Next, create a new ObjectInputStream object, passing the input stream to its constructor.
Wrap the ObjectInputStream constructor in a try-catch block to handle any potential exceptions, such as IOException or ClassNotFoundException.
Use the readObject() method of the ObjectInputStream to read serialized objects from the input stream.
Once you have finished reading objects from the input stream, close the ObjectInputStream to release any resources it may be holding.

Method Of ObjectInputStream:

Methods	Description
readObject():	Reads and deserializes the next object from the input stream.
read():	Reads a byte of data from the input stream.
readByte():	Reads a byte value from the input stream.
readShort():	Reads a short value from the input stream.
close():	Closes the ObjectInputStream and releases any system resources associated with it.
remove(element):	Removes the first occurrence of the specified element from the Vector.
readFloat():	Reads a float value from the input stream.
available():	Returns an estimate of the number of bytes that can be read from the input stream.

There are many more methods available, but these are the most commonly used ones.

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Example 1: Java ObjectInputStream

Run

import java.io.FileInputStream;

import java.io.FileOutputStream;

import java.io.ObjectInputStream;

import java.io.ObjectOutputStream;

 
class Main
{
  
public static void main (String[]args)
  {
    
 
int data1 = 72;
    
String data2 = "PrepInsta is a e-learning Platform";
    
 
try
    {
      
FileOutputStream file = new FileOutputStream ("file.txt");
      
ObjectOutputStream output = new ObjectOutputStream (file);
      
 
	// Writing to the file using ObjectOutputStream
	output.writeInt (data1);
      
output.writeObject (data2);
      
 
FileInputStream fileStream = new FileInputStream ("file.txt");
      
	// Creating an object input stream
	ObjectInputStream objStream = new ObjectInputStream (fileStream);
      
 
	//Using the readInt() method
	System.out.println ("Integer data :" + objStream.readInt ());
      
 
	// Using the readObject() method
	System.out.println ("String data: " + objStream.readObject ());
      
 
output.close ();
      
objStream.close ();
    
} 
catch (Exception e)
    {
      
e.getStackTrace ();

} 
} 
}

Output

Integer data :72
String data: PrepInsta is a e-learning Platform

Explanation:

The program first writes an int and a String to a file using ObjectOutputStream, and then reads them back using ObjectInputStream. It uses the writeInt() and writeObject() methods of ObjectOutputStream to write the int and String to the file, and the readInt() and readObject() methods of ObjectInputStream to read them back.

Example 2 : Java ObjectInputStream Class

Run

import java.io.*;

public class Main {
    public static void main(String[] args) {
        // Create an object to be written to a file
        Person person = new Person("John", "Doe", 30);

        try {
            // Write the object to a file using ObjectOutputStream
            FileOutputStream fileOutputStream = new FileOutputStream("person.dat");
            ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream);
            objectOutputStream.writeObject(person);

            // Read the object from the file using ObjectInputStream
            FileInputStream fileInputStream = new FileInputStream("person.dat");
            ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);
            Person readPerson = (Person) objectInputStream.readObject();

            // Print the read object
            System.out.println("Name: " + readPerson.getFirstName() + " " + readPerson.getLastName());
            System.out.println("Age: " + readPerson.getAge());

            // Close the streams
            objectOutputStream.close();
            objectInputStream.close();
        } catch (IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

class Person implements Serializable {
    private String firstName;
    private String lastName;
    private int age;

    public Person(String firstName, String lastName, int age) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.age = age;
    }

    public String getFirstName() {
        return firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public int getAge() {
        return age;
    }
}

Output

Name: John Doe
Age: 30

Explanation:

we create a Person object and write it to a file using ObjectOutputStream. Then we read the Person object from the file using ObjectInputStream and print its properties.

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Java ObjectInputStream Class

What is Java ObjectInputStream Class?

Working of ObjectInputStream

Create an ObjectInputStream

Method Of ObjectInputStream:

Example 1: Java ObjectInputStream

Output

Example 2 : Java ObjectInputStream Class

Output

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