Java Object Serialization by using Java I/O Streams

The task is to store different objects of classes in a physically located file on hard disk. For this to store objects and their states (including the values of their data members) we have to make those classes serializeable. Use Standard Java I/O streams FileOutputStream, ObjectOutputStream to write/store to file and FileInputStream, ObjectInputStream streams to read objects from the file. After reading all objects from the file, have to type caste to their original class type and then get data from these casted objects.

Following is the code that you can see and can also download. MyObjects.java

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.NotSerializableException;
import java.io.EOFException;

public class MyObjects {

private static FileOutputStream fos = null;
private static ObjectOutputStream oos = null;
private static FileInputStream fis = null;
private static ObjectInputStream ois = null;

public static void main(String args[]) {
// Creating Serialized Objects those we will write to file
Student student = new Student();
student.setStudent_id(100);
student.setName(“Faisal”);
student.setTemp(“This field will not be serialized”);

Teacher teacher = new Teacher();
teacher.setTeacher_id(99);
teacher.setName(“Tahir”);
teacher.setTemp(“This field will not be serialized”);

Subject subject = new Subject();
subject.setBook_id(999);
subject.setBook_name(“Thinking in Java”);
subject.setTemp(“This field will not be serialized”);

// Specifing the path of file. Its relative to java source file
File file = new File(“Object.txt”);
try {
// Writing Objects to file
fos = new FileOutputStream(file);
oos = new ObjectOutputStream(fos);
oos.writeObject(student);
oos.writeObject(teacher);
oos.writeObject(subject);

oos.flush();// Pushing the data into the file
oos.close();// Closing the output stream
// Opening input stream from the file
fis = new FileInputStream(file);
ois = new ObjectInputStream(fis);
Object obj = null;
// Reading & Iterating the object from file
while ((obj = ois.readObject()) != null) {
if (obj instanceof Student) {
student = (Student) obj;
System.out.println(student.toString());
} else if (obj instanceof Teacher) {
teacher = (Teacher) obj;
System.out.println(teacher.toString());
} else if (obj instanceof Subject) {
subject = (Subject) obj;
System.out.println(subject.toString());
}
}
ois.close();// Closing the Input streams
student = null;
teacher = null;
subject = null;
file = null;
obj = null;
} catch (NotSerializableException e) {
System.out.println(e.getMessage());
e.printStackTrace();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (EOFException e) {
System.out.println(“Finished File Reading”);
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
} finally {
if (ois != null) {
ois = null;
}
if (oos != null) {
oos = null;
}
}
}
}

class Student implements Serializable {
private int student_id;
private String name;
private transient String temp;

// Getters & Setters Methods
public int getStudent_id() {
return student_id;
}

public void setStudent_id(int student_id) {
this.student_id = student_id;
}

public String getName() {
return name;
}

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

public String getTemp() {
if (this.temp == null)
return “Transient & Can’t be serialzied”;
return temp;
}

public void setTemp(String temp) {
this.temp = temp;
}

// toString() method for returning the current object’s concatinated values
public String toString() {
return “[Student -> ID: " + getStudent_id() + " , Name: " + getName()
+ " , " + getTemp() + " ]“;
}
}

class Teacher implements Serializable {
private int teacher_id;
private String name;
private transient String temp;

// Getters & Setters Methods
public int getTeacher_id() {
return teacher_id;
}

public void setTeacher_id(int teacher_id) {
this.teacher_id = teacher_id;
}

public String getName() {
return name;
}

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

// toString() method for returning the current object’s concatinated values
public String toString() {
return “[Teacher -> ID: " + getTeacher_id() + " , Name: " + getName()
+ " , " + getTemp() + " ]“;
}

public String getTemp() {
if (this.temp == null)
return “Transient & Can’t be serialzied”;
return temp;
}

public void setTemp(String temp) {
this.temp = temp;
}
}

class Subject implements Serializable {
private int book_id;
private String book_name;
private transient String temp;

// Getters & Setters Methods
public int getBook_id() {
return book_id;
}

public void setBook_id(int book_id) {
this.book_id = book_id;
}

public String getBook_name() {
return book_name;
}

public void setBook_name(String book_name) {
this.book_name = book_name;
}

// toString() method for returning the current object’s concatinated values
public String toString() {
return “[Book -> ID: " + getBook_id() + " , Name: " + getBook_name()
+ " , " + getTemp() + " ]“;
}

public String getTemp() {
if (this.temp == null)
return “Transient & Can’t be serialzied”;
return temp;
}

public void setTemp(String temp) {
this.temp = temp;
}
}