Serialization and externalization both are the processes of converting an object to stream byte and storing byte stream in database or memory. The class which implements java.io.Serializable interface can be serialized. On the other hand, externalization used for custom serialization based on the requirement in the application. Externalization extends java.io.Serializable.
| Sr. No. | Key | Serialization | Externalization |
|---|---|---|---|
| 1 | Interface | Serialization is a marker interface | Externalization contains two methods readExternal and writeExternal. |
| 2 | Implementation logic | The class which is implementing this interface gives the responsibility to JVM for serializing or persist java object. JVM use readObject and writeObject for serialization | Externalization provides implementation logic control to the application by overriding readExternal and writeExternal methods. |
| 3 | Way to ignore variables | In serialization, JVM ignores transient variable during serialization and deserialization of java object | Programmer can write their own logic to ignore some of the variables during externalization of java object |
| 4 | Performance | In serializable interface uses reflection which causes relatively slow performance. | Externalizable gives full control over the implementation approach. |
| 5 | Object serialization with inheritance | 1. If the superclass is not serializable then the subclass still can be serialized. 2. If a subclass is not serialized but superclass is automatically serializable | We can apply this to externalizable as well. |
Example of Externalizable
class ExternalizableExample implements Externalizable {
Integer id;
@Override
public void writeExternal(ObjectOutput out) throws IOException {
out.writeInt( id );
}
@Override
public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
this.id = in.readInt();
}
}Example of Serializable
class SerializableExample implements Serializable {
private static final long serialVersionUID = 5081877L;
String name;
}