Java provides a mechanisms to represent an object as a sequence of bytes, including
After a serialized object has been written into a file, it can be read from the file and deserialized.
The entire process is JVM independent, meaning an object can be serialized on one platform and deserialized on an entirely different platform.
It's all about
ObjectInputStream and ObjectOutputStreamThe classes ObjectInputStream and ObjectOutputStream are high-level streams that contain the methods for serializing and deserializing an object.
ObjectOutputStream has a method to serialize an Object and sends it to the output stream.
public final void writeObject(Object x) throws IOExceptionSimilarly, ObjectInputStream contains the following method to deserialize an object from an input stream.
public final Object readObject() throws IOException, ClassNotFoundExceptionThe return value is Object, so you will need to cast it to its appropriate data type.
SerializableTo serialize instances of a class, we need to
Serializable interface, and public class Employee implements java.io.Serializable {
public String name;
public transient int SSN;
public Employee(String name, int SSN) {
this.name = name;
this.SSN = SSN;
}
public void mailCheck() {
System.out.println("Mailing a check to " + name + ". ");
}
}When serializing an object to a file, the standard convention in Java is to give the file a .ser extension.
import java.io.*;
public class SerializerDemo {
public static void main(String [] args) {
String fileName = "resources/employee.ser";
Employee e1 = new Employee("Rick", 131241);
Employee e2 = new Employee("Morty", 12314);
Employee e3 = new Employee("Summer", 512512);
try (ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(fileName))){
out.writeObject(e1);
out.writeObject(e2);
out.writeObject(e3);
System.out.printf("Serialized data is saved in %s",fileName);
}catch(IOException i) {
i.printStackTrace();
}
}
}The return value of readObject() is cast to an Employee reference.
If the JVM can't find a class during the deserialization of an object, it throws a ClassNotFoundException
The deserialized employees all have their SSNs set to 0 because the SSN field is transient
public class DeserializerDemo {
public static void main(String[] args) {
ArrayList<Employee> employees = new ArrayList<>();
String fileName = "resources/employee.ser";
try (ObjectInputStream in = new ObjectInputStream(new FileInputStream(fileName))) {
try {
while (true)
employees.add((Employee) in.readObject());
} catch (IOException e) {
System.out.println("Finished reading file.");
} catch (ClassNotFoundException e) {
System.out.println("Employee class not found");
e.printStackTrace();
return;
}
} catch (IOException i) {
i.printStackTrace();
return;
}
System.out.println("Deserialized employees...");
employees.forEach(e -> System.out.printf("Name: %s, SSN: %s%n", e.name, e.SSN));
}
}