Difference Between ObjectInputStream and ObjectOutputStream in Java

In a software project, in many instances, there are necessities to transfer the data, and it can be handled by using ObjectOutputStream and ObjectInputStream from Java IO packages. Usually, the data is written in binary format and hence we cannot view the contents. Serialization is the process of writing an object to an output stream. We can write a class object itself, which contains a combination of primitive datatype and graphs of Java objects. Deserialization is the process of reconstructing an object from an input stream.

Implementation: Let us see the ObjectOutputStream with an is illustrated for which we create a POJO class called “VehicleSpecifications”. 

Note: It should implement Serializable, otherwise, java.io.NotSerializableException will be thrown.

Example 1:

Java

// Java Program simply illustrating POJO / Model class

// Importing input output class
import java.io.Serializable;

// Class 1
// Implements Serializable  for POJO class to avoid
// NotSerializableException will be thrown
public class VehicleSpecifications implements Serializable {

    // Member variables of this class
    private String color;
    private String type;
    private String name;
    private double price;

    // Constructors of this class

    // Constructor- 1
    // Default constructor
    public VehicleSpecifications() {}

    // Constructor- 2
    // Parameterized constructor accepting all attributes and
    // helps to create a VehicleSpecifications class
    public VehicleSpecifications(String color, String type,
                                 String name, double price)
    {

        // This keyword refers to current object itself
        this.color = color;
        this.type = type;
        this.name = name;
        this.price = price;
    }

    // Methods of this class
    // Specifically  Getter and Setter methods

    // Method 1
    public double getPrice() { return price; }

    // Method 2
    public void setPrice(double price)
    {
        this.price = price;
    }

    // Method 3
    public String getName() { return name; }

    // Method 4
    public void setName(String name) { this.name = name; }

    // Method 5
    public String getColor() { return color; }

    // Method 6
    public void setColor(final String color)
    {
        this.color = color;
    }

    // Method 7
    public String getType() { return type; }

    // Method 8
    public void setType(final String type)
    {
        this.type = type;
    }
}

No output is as till now by far we have implemented just the constructors and defined body of methods including getters and setters. 

Now let us create a few vehicle specifications and write them in a file. As VehicleSpecifications implemented Serializable functionality, the data can be written to a file in a binary format. For this we will be using “writeObject” function and by using that we can write class attributes using write methods provided by ObjectOutputStream.

Example 2:

Java

// Class 2
// Java Program to Create Few VehicleSpecification and
// Writing in a File

// Importing required classes from packages
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.util.ArrayList;
import java.util.List;

// Main class
public class VehicleSpecificationsSerializer {

    // main driver method
    public static void main(String[] args)
    {

        // Output file been passed in a string
        String sampleOutputFile = "VehicleSpecification.db";

        // Try block to check for exceptions
        try {

            // Create a objectoutputstream accepting the
            // file name as VehicleSpecification.db
            ObjectOutputStream vehicleObjectOutput
                = new ObjectOutputStream(
                    new FileOutputStream(sampleOutputFile));

            // Create a list of VehicleSpecifications class
            List<VehicleSpecifications> listSpecifications
                = new ArrayList<VehicleSpecifications>();

            // Add the necessary data using standard add()
            // method Custom input
            listSpecifications.add(
                new VehicleSpecifications("Radiant Red",
                                          "SUV", "WR-V",
                                          1700000f));

            listSpecifications.add(
                new VehicleSpecifications("Metallic Blue",
                                          "SUV", "WR-V",
                                          1800000f));

            listSpecifications.add(
                new VehicleSpecifications(
                    "Black", "SUV", "WR-V", 1900000f));

            // We are writing the whole object into the file
            // which is a list item of VehicleSpecifications
            // object
            vehicleObjectOutput.writeObject(
                listSpecifications);

            // Closing the connection to release memory
            vehicleObjectOutput.close();
        }

        // Catch block to handle the exceptions
        catch (IOException ex) {

            // Print the exceptions along with line number
            // using printStackTrace() method
            ex.printStackTrace();
        }
    }
}

Note: On execution of the above code, we can see that the data is written in a binary format that means, it is a non-readable format only.

So In order to get the data in a readable format, we are using ObjectInputStream and as we have to retrieve the class object data(i.e. VehicleSpecifications data), we need to use readObject() method, which can read class attributes using read() methods provided by ObjectInputStream.

Example 3:

Java

// Java Program to make above code human-readable

// Importing classes from required packages
import java.io.FileInputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.util.ArrayList;
import java.util.List;

// Main class
public class VehicleSpecificationsDeSerializer {

    // main driver method
    public static void main(String[] args)
    {

        // Input file
        String sampleInputFile = "VehicleSpecification.db";

        // Try block to check for exceptions
        try {

            // Creating an object of ObjectInputStream class
            ObjectInputStream vehicleObjectInputStream
                = new ObjectInputStream(
                    new FileInputStream(sampleInputFile));

            // Creating a List class object
            // Declaring object of user defined type
            // (VehicleSpecifications)
            List<VehicleSpecifications>
                vehicleSpecificationsListData
                = new ArrayList<VehicleSpecifications>();

            // Using readObject, bringing back the whole
            // list item of VehicleSpecifications into scope

            // readObject which can read class attributes
            // using read methods provided by
            // ObjectInputStream.
            vehicleSpecificationsListData
                = (ArrayList<VehicleSpecifications>)
                      vehicleObjectInputStream.readObject();

            // Iterating over above object created
            for (int i = 0;
                 i < vehicleSpecificationsListData.size();
                 i++) {

                VehicleSpecifications vehicleSpecifications
                    = vehicleSpecificationsListData.get(i);

                // Print and display commands
                System.out.println(
                    "Color .."
                    + vehicleSpecifications.getColor());
                System.out.println(
                    "Name .."
                    + vehicleSpecifications.getName());
                System.out.println(
                    "Price .."
                    + vehicleSpecifications.getPrice());
                System.out.println(
                    "Type .."
                    + vehicleSpecifications.getType());
            }
            // Closing the resources to free up memory space
            vehicleObjectInputStream.close();
        }

        // Catch block to handle the exceptions

        // Catch block 1
        // Handling input output  exceptions
        catch (IOException ex) {

            // Printing the line number where exception
            // occurred using printStackTrace() method
            ex.printStackTrace();
        }

        // Catch block 2
        // Handle exception if class not found
        catch (ClassNotFoundException e) {

            // Again, printing the line number where
            // exception occurred using printStackTrace()
            // method
            e.printStackTrace();
        }
    }
}

Output:

Output explanation:

So, we are seeing the output in a human-readable format. So our entire set of class objects can be portable using ObjectInput and ObjectOutput streams provided by java.io packages. Hence, now let us finally discuss out the differences between ObjectOutputStream and ObjectInputStream after having an internal workflow understanding of them. They are illustrated below in a tabular format shown as below:

ObjectOutputStream	ObjectInputStream
Writes Java objects	Reads Java objects
Using ArrayList, we can write multiple Java objects	Via ArrayList, we can read and retrieve multiple Java objects
By default, ArrayList is serializable, and hence no need to implement serializable if we are writing ArrayList of objects like String, but the elements should be serializable. writeObject() is used to write ArrayList of data	During deserialization of ArrayList object, readObject() is used to read the ArrayList of data
If we are using a class object(like the example as we discussed above), the class should implement serializable and then only while using writeObject() method, java.io.NotSerializableException will not be thrown	We need to cast the same format of object while using readObject()
writeObject() method writes the serialized data in binary format	readObject() method deserializes and reads the data
The binary format is not readable. Though we are passing primitive data like String, double, etc., while writing, the data is getting stored in binary format.	In order to get the data in perfect class format, we need to use ObjectInputStream which deserializes data and we can get all primitive data that is written
As a whole object, it is getting written, there is no loss of data provided the object is serialized and written in a proper format	Similarly, whole object is read, there is no loss of data, and we can easily iterate the data also.
Not only writing class objects by means writeObject(), it also supports other write methods like as depicted below and many more methods to write for each and every data type.  write(byte[] buffer)-> Writes an array of bytes. writeBoolean(boolean value) -> Write boolean value writeDouble(double value)-> Write 64 bit double value writeInt(int value)-> Writes 32 bit int	Not only reading class objects by means readObject(), it also supports other read methods like depicted as below and many more methods to read each and every datatype. read()-> Reads byte of data readBoolean() -> To read  a boolean. readDouble()-> To read a 64 bit double. readInt()->To Read a 32 bit int.
Possible exceptions for ObjectOutputStream is as follows: IOException – in case of any I/O error occurs during writing stream header SecurityException  NullPointerException – if OutputStream not initialized and hence it may be null	Possible exceptions for ObjectInputStream is as follows: StreamCorruptedException – Incorrect stream header IOException – In case of any I/O error occurs while reading stream header SecurityException  NullPointerException – if Inputstream not initialized and hence it may be null
Possible exceptions for writeObject is as follows: InvalidClassException – Serialization of class should be correct and if something is wrong. NotSerializableException – Some object to be serialized does not implement the java.io.Serializable interface. This will commonly occur and hence it is mandatory to make the class to implement Serializable IOException – During writing, if IO error occur by the underlying OutputStream.	Possible exceptions for readObject is as follows: InvalidClassException – Serialization of class should be correct and if something is wrong. ClassNotFoundException – Class of a serialized object should be available and if cannot be found. IOException – During reading, if IO error occur by the underlying InputStream StreamCorruptedException  OptionalDataException