The document discusses Java serialization and the Externalizable interface. It provides examples of how to serialize and deserialize objects to allow their state to be written to a stream and restored later. The key points covered include: - Using the Serializable interface to allow object serialization - Implementing Externalizable for more control and better performance than Serializable - Techniques for serializing singletons, enums, and collections for Externalizable - Performance comparisons showing Externalizable can provide significant speed improvements over Serializable

1. JOURNEY INTO THE WORLD OF JAVA:
JAVA SERIALIZATION

2. public class Vehicle{
public String number = "";
public Vehicle(){
System.out.println("Vehicle::Vehicle()");
}
}public class Car extends Vehicle implements Serializable{
public String mark = "";
public String model = "";
public Car(){
System.out.println("Car::Car()");
}
public Car(String mark, String model){
System.out.println("Car::Car(String, String)");
this.mark = mark;
this.model = model;
}
}
Serializable

3. public class Vehicle{
public String number = "";
public Vehicle(){
System.out.println("Vehicle::Vehicle()");
}
}
Serializable

4. public class Car extends Vehicle implements Serializable{
public String mark = "";
public String model = "";
public Car(){
System.out.println("Car::Car()");
}
public Car(String mark, String model){
System.out.println("Car::Car(String, String)");
this.mark = mark;
this.model = model;
}
}
Serializable

5. System.out.println("Creating...");
Car car = new Car("Zaz", "Forza");
car.number = "AA0001BP";
ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
ObjectOutputStream objectOutputStream = new ObjectOutputStream(byteArrayOutputStream);
System.out.println("Serializing...");
objectOutputStream.writeObject(car);
objectOutputStream.flush();
byteArrayOutputStream.flush();
objectOutputStream.close();
byteArrayOutputStream.close();
ByteArrayInputStream bais = new ByteArrayInputStream(byteArrayOutputStream.toByteArray());
ObjectInputStream ois = new ObjectInputStream(bais);
System.out.println("Deserializing...");
Car car2 = (Car)ois.readObject();
System.out.println("car2.number=" + car2.number);
System.out.println("car2.mark=" + car2.mark);
System.out.println("car2.model=" + car2.model);
Serializable

6. System.out.println("Creating...");
Car car = new Car("Zaz", "Forza");
car.number = "AA0001BP";
Serializable

7. ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
ObjectOutputStream objectOutputStream = new ObjectOutputStream(byteArrayOutputStream);
System.out.println("Serializing...");
objectOutputStream.writeObject(car);
objectOutputStream.flush();
byteArrayOutputStream.flush();
objectOutputStream.close();
byteArrayOutputStream.close();
Serializable

8. ByteArrayInputStream bais = new
ByteArrayInputStream(byteArrayOutputStream.toByteArray());
ObjectInputStream ois = new ObjectInputStream(bais);
System.out.println("Deserializing...");
Car car2 = (Car)ois.readObject();
System.out.println("car2.number=" + car2.number);
System.out.println("car2.mark=" + car2.mark);
System.out.println("car2.model=" + car2.model);
Serializable

9. Creating...
Vehicle::Vehicle()
Car::Car(String, String)
Serializing...
Deserializing...
Vehicle::Vehicle()
car2.number=
car2.mark=Zaz
car2.model=Forza
Serializable

10. Serializable. Secure
private void writeObject(java.io.ObjectOutputStream stream) throws java.io.IOException;
private void readObject(java.io.ObjectInputStream stream) throws java.io.IOException,
ClassNotFoundException;
private void java.io.ObjectInputStream.defaultWriteObject(java.io.ObjectOutputStream stream)
throws java.io.IOException;
private void java.io.ObjectInputStream.defaultReadObject(java.io.ObjectInputStream stream)
throws java.io.IOException,
ClassNotFoundException;
public interface java.io.ObjectInputValidation {
public void validateObject() throws InvalidObjectException;
}

11. Serializable. Features
public class ArrayList extends AbstractList implements List,
Cloneable,Serializable {
private transient Object elementData[];
private int size;
...
}
class List implements Serializable {
List next;
private static final ObjectStreamField[] serialPersistentFields
= {new ObjectStreamField("next", List.class)}
};

12. • Adding new fields to a class
• Changing the fields from static to nonstatic
• Changing the fields from transient to nontransient
Serializable. Can Manage Automatically
private static final long serialVersionUID = 3329999866918906824L;

13. private/public/protected Object readResolve() throws ObjectStreamException
private/public/protected Object writeReplace() throws ObjectStreamException
Serializable. Singleton

14. Serializable. Singleton
public class Singleton implements Serializable {
private static final long serialVersionUID = 8413502725007695828L;
private static Singleton instance = null;
public String name = "";
private Singleton(){};
public static Singleton getInstance(){
if (instance == null){
instance = new Singleton();
}
return instance;
}
private Object readResolve() throws ObjectStreamException{
instance.name = this.name;
return instance;
}
}

15. Serializable. Singleton
private Object readResolve() throws ObjectStreamException{
instance.name = this.name;
return instance;
}
}

16. Serializable. Singleton
Singleton instance1 = Singleton.getInstance();
instance1.name = "instance1";
............................................................................
System.out.println("Serializing...");
System.out.println("instance1.name:" + instance1.name);
..............................................................................
objectOutputStream.writeObject(instance1);
............................................................................
instance1.name = "instance2";
............................................................................
System.out.println("Deserializing...");
Singleton instance2 = (Singleton)ois.readObject();
if(instance1 == instance2){
System.out.println("instance1 == instance2");
}else{
System.out.println("instance1 != instance2");
}
System.out.println("instance2.name:" + instance2.name);

17. Serializable. Singleton
Singleton instance1 = Singleton.getInstance();
instance1.name = "instance1";
............................................................................
System.out.println("Serializing...");
System.out.println("instance1.name:" + instance1.name);
..............................................................................
objectOutputStream.writeObject(instance1);
............................................................................
instance1.name = "instance2";

18. Serializable. Singleton
............................................................................
System.out.println("Deserializing...");
Singleton instance2 = (Singleton)ois.readObject();
if(instance1 == instance2){
System.out.println("instance1 == instance2");
}else{
System.out.println("instance1 != instance2");
}
System.out.println("instance2.name:" + instance2.name);

19. Serializable. Singleton
Serializing...
instance1.name:instance1
Deserializing...
instance1 == instance2
instance2.name:instance1

20. Serializable. ENUM
public enum Color {
RED("red"),GREEN("green"),BLUE("blue");
private Color(String name){
this.name = name;
}
public String getName(){
return name;
}
private String name;
}

21. Serializable. ENUM
Color red1 = Color.RED;Color green1 = Color.GREEN;Color blue1 = Color.BLUE;
.....................................
System.out.println("Serializing...");
objectOutputStream = new ObjectOutputStream(byteArrayOutputStream);
objectOutputStream.writeObject(red1);
objectOutputStream.writeObject(green1);
objectOutputStream.writeObject(blue1);
.....................................
System.out.println("Deserializing...");
Color red2 = (Color)ois.readObject();
Color green2 = (Color)ois.readObject();
Color blue2 = (Color)ois.readObject();
if(red1 == red2) System.out.println("red1 == red2");
if(green1 == green2) System.out.println("green1 == green2");
if(blue1 == blue2) System.out.println("blue1 == blue2");

22. Serializable. ENUM
Color red1 = Color.RED;
Color green1 = Color.GREEN;
Color blue1 = Color.BLUE;
.....................................
System.out.println("Serializing...");
objectOutputStream = new ObjectOutputStream(byteArrayOutputStream);
objectOutputStream.writeObject(red1);
objectOutputStream.writeObject(green1);
objectOutputStream.writeObject(blue1);

23. Serializable. ENUM
.....................................
System.out.println("Deserializing...");
Color red2 = (Color)ois.readObject();
Color green2 = (Color)ois.readObject();
Color blue2 = (Color)ois.readObject();
if(red1 == red2) System.out.println("red1 == red2");
if(green1 == green2) System.out.println("green1 == green2");
if(blue1 == blue2) System.out.println("blue1 == blue2");

24. Serializable. ENUM
Serializing...
Deserializing...
red1 == red2
green1 == green2
blue1 == blue2

25. Serializable. ENUM
writeObject
writeReplace
serialPersistentFields
serialVersionUID

26. public interface Externalizable extends java.io.Serializable {
void writeExternal(ObjectOutput out) throws IOException;
void readExternal(ObjectInput in) throws IOException, ClassNotFoundException;
}
Externalizable

27. Externalizable. Performance
public class ItemExt implements Externalizable{
private int fieldInt;
private boolean fieldBoolean;
private long fieldLong;
private float fieldFloat;
private double fieldDouble;
private String fieldString;
public ItemExt(){
this(0,true,0,0,0,"");
}
..................................................

28. Externalizable. Performance
public void writeExternal(ObjectOutput out) throws IOException {
out.writeInt(fieldInt);
out.writeBoolean(fieldBoolean);
out.writeLong(fieldLong);
out.writeFloat(fieldFloat);
out.writeDouble(fieldDouble);
out.writeUTF(fieldString);
}
public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
fieldInt = in.readInt();
fieldBoolean = in.readBoolean();
fieldLong = in.readLong();
fieldFloat = in.readFloat();
fieldDouble = in.readDouble();
fieldString = in.readUTF();
}

29. Externalizable. Performance
public abstract class ContainerExt implements Externalizable{
protected List<ItemExt> items;
public ContainerExt(){
items = new LinkedList<ItemExt>();
}
public void addItem(ItemExt item){
items.add(item);
}
..................................................
}

30. /*ContainerExt1*/public void writeExternal(ObjectOutput out) throws IOException {
out.writeObject(items);
}
public void readExternal(ObjectInput in) throws
IOException, ClassNotFoundException {
items = (List<ItemExt>)in.readObject();
}
Externalizable. Performance

31. Externalizable. Performance
/*ContainerExt2*/
public void writeExternal(ObjectOutput out) throws IOException {
out.writeInt(items.size());
for(Externalizable ext : items)
out.writeObject(ext);
}
public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
int count = in.readInt();
for(int i=0; i<count; i++){
ItemExt ext = (ItemExt)in.readObject();
items.add(ext);
}
}

32. /*ContainerExt3*/
public void writeExternal(ObjectOutput out) throws IOException {
out.writeInt(items.size());
for(Externalizable ext : items)
ext.writeExternal(out);
}
public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException{
int count = in.readInt();
for(int i=0; i<count; i++){
ItemExt ext = new ItemExt();
ext.readExternal(in);
items.add(ext);
}
}
Externalizable. Performance

33. [java] Creating 100000 objects
[java] Serializable: written in 971ms, readed in 1353
[java] Externalizable1: written in 1026ms, readed in 1129
[java] Externalizable2: written in 909ms, readed in 1876
[java] Externalizable3: written in 49ms, readed in 268
06/16/2013 08:24 PM 5,547,651 cont.ser
06/16/2013 08:24 PM 5,747,559 contExt1.ser
06/16/2013 08:24 PM 5,747,521 contExt2.ser
06/16/2013 08:24 PM 4,871,155 contExt3.ser
Externalizable. Performance

34. https://github.com/MikhailGevak/Serialize