Java ObjectInputStream and ObjectOutputStream Example

Anirudh BhatnagarOctober 6th, 2014Last Updated: October 6th, 2014

0 240 2 minutes read

In this example we will see how we can use Java’s ObjectInputStream and ObjectOutputStream classes to serialize objects and store them as a file or any other storage accessible by Output Stream; read them again, deserialize it into an object and use it.

ObjectOutputStream Example

So, first we will see how to write an object into a File using FileOutputStream object. We will wrap FileOutputStream in a ObjectOutputStream and write into the file using ObjectOutputStream's writeObject() method.

Important thing to not here is that the object which is to be serialised needs to implement java.io.Serializable interface and hence implement the toString() method.

Lets see this in example :

User.java

package com.javacodegeeks.example;
 
import java.io.Serializable;
 
public class User implements Serializable {
 
    /**
     * @author anirudh
     */
    private static final long serialVersionUID = 8309080721495266420L;
    private String firstName;
    private String lastName;
    private String email;
 
    public User(String firstName, String lastName, String email) {
        super();
        this.firstName = firstName;
        this.lastName = lastName;
        this.email = email;
    }
 
    //..getters and setters...
 
    /**
     * Two users are equal if their firstName, lastName and email address is
     * same.
     */
    @Override
    public boolean equals(Object obj) {
        return (this.firstName.equals(((User) obj).firstName)
                && this.lastName.equals(((User) obj).lastName) && this.email
                    .equals(((User) obj).email));
    }
 
    @Override
    public String toString() {
        return getFirstName() + " " + getLastName() + " " + getEmail();
    }
 
}

JavaObjectInputOutputStreamExample.java

package com.javacodegeeks.example;
 
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
 
/**
 * 
 * @author anirudh
 */
public class JavaObjectInputOutputStreamExample {
 
    public static void main(String[] args) {
 
        try {
 
            // Store Serialized User Object in File
            FileOutputStream fileOutputStream = new FileOutputStream(
                    "/Users/anirudh/user.txt");
            User user = new User("Anirudh", "lastName", "email");
            ObjectOutputStream output = new ObjectOutputStream(fileOutputStream);
            output.writeObject(user);
            output.close();
 
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } 
    }
 
}

ObjectInputStream Example

In the above example we wrote the user object into a file. In order to read from this file , we will use ObjectInputStream. This class enables us to read Java Objects from InputStream instead of only bytes. We can wrap an InputStream in a ObjectInputStream and then can read objects from it.

Lets see this in the example :

JavaObjectInputOutputStreamExample.java

package com.javacodegeeks.example;
 
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
 
/**
 * 
 * @author anirudh
 * 
 */
public class JavaObjectInputOutputStreamExample {
 
    public static void main(String[] args) {
 
        try {
 
            //Read from the stored file
            FileInputStream fileInputStream = new FileInputStream(new File(
                    "/Users/anirudh/test.txt"));
            ObjectInputStream input = new ObjectInputStream(fileInputStream);
            User user2 = (User) input.readObject();
            System.out.println(user2.getFirstName());
            input.close();
 
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
 
}

Output :

Anirudh

In the example we read a file which was previously written by ObjectOutputStream as a serialised object. Here, we have deserialised it using ObjectInputStream.readObject() method.

This was an example of using ObjectInputStream and ObjectOutputStream classes in Java.

Download
You can download the full source code of this example here : JavaObjectInputOutputStreamExample.zip