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Why HttpServlet implements Serializable interface

Bishnu Mishra

Joined: Sep 01, 2006
Posts: 2
GenericServlet implements Serializable and HttpServlet extends GenericServelet then Serialization facility available to HttpServlet.. Then why HttpServlet implements Serializable interface?
Stefan Evans

Joined: Jul 06, 2005
Posts: 1580
Why not?
It is probably more for documentation purposes than anything else - ie just so the javadoc will explicitly state it, rather than the reader having to KNOW that it extends a class that implements serializable.
Cameron Wallace McKenzie
author and cow tipper
Saloon Keeper

Joined: Aug 26, 2006
Posts: 4968

Serializable - The Breakfast Interface

Because Serializable is a marker interface, any class that is indeed serializable should include this interface in its class declaration.

I can create a class with all, boring Java data types and call it serializable. Then I can subclass it and add an instance variable that is of type DataSource or DatabaseConnection, which isn't declared as being transient, and isn't serializable. In this case, I have extended a class that IS serializable, but my own class is indeed NOT serializable.

Does that make any sense?

By the way, if you extended a Serializable class, but added instance variables that weren't Serializable, would you be a "serial killer?"

Christophe Verré

Joined: Nov 24, 2005
Posts: 14688

I'm not satisfied with the above answers
There must be a decent reason to decide to set this class Serializable. Servlets are not supposed to hold states, so I can't understand either why it has to be Serializable. Any relation to distributed environments ?

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David O'Meara

Joined: Mar 06, 2001
Posts: 13459

Servlets are allowed to hold state, they just shouldn't hold user state. I can think of better ways to do it, but a cluster may require Servlets to be Serializable.
It is sorta covered in the JavaRanch Style Guide.
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