Java Serialization Example Tutorial, Serializable, serialVersionUID

Java Serialization Example Tutorial, Serializable, serialVersionUID

Java Serialization Methods

We have seen that java serialization is automatic and all we need is implementing Serializable interface. The implementation is present in the ObjectInputStream and ObjectOutputStream classes. But what if we want to change the way we are saving data, for example we have some sensitive information in the object and before saving/retrieving we want to encrypt/decrypt it. That’s why there are four methods that we can provide in the class to change the serialization behavior.

If these methods are present in the class, they are used for serialization purposes.

1. readObject(ObjectInputStream ois): If this method is present in the class, ObjectInputStream readObject() method will use this method for reading the object from stream.
2. writeObject(ObjectOutputStream oos): If this method is present in the class, ObjectOutputStream writeObject() method will use this method for writing the object to stream. One of the common usage is to obscure the object variables to maintain data integrity.
3. Object writeReplace(): If this method is present, then after serialization process this method is called and the object returned is serialized to the stream.
4. Object readResolve(): If this method is present, then after deserialization process, this method is called to return the final object to the caller program. One of the usage of this method is to implement Singleton pattern with Serialized classes. Read more at Serialization and Singleton.

Usually while implementing above methods, it’s kept as private so that subclasses can’t override them. They are meant for serialization purpose only and keeping them private avoids any security issue.
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