Init and Destroy
Just like applets, servlets can define
init()
and destroy()
methods. A servlet’s init(ServletConfig)
method is called by the server immediately after the server
constructs the servlet’s instance. Depending on the server and
its configuration, this can be at any of these times:
When the server starts
When the servlet is first requested, just before the
service()
method is invokedAt the request of the server administrator
In any case, init()
is guaranteed to be called
before the servlet handles its first request.
The init()
method is typically used to perform
servlet initialization—creating or loading objects that are
used by the servlet in the handling of its requests. Why not use a
constructor instead? Well, in JDK 1.0 (for which servlets were
originally written), constructors for dynamically loaded Java classes
(such as servlets) couldn’t accept arguments. So, in order to
provide a new servlet any information about itself and its
environment, a server had to call a servlet’s
init()
method and pass along an object that
implements the ServletConfig
interface. Also, Java
doesn’t allow interfaces to declare constructors. This means
that the javax.servlet.Servlet
interface cannot
declare a constructor that accepts a ServletConfig
parameter. It has to declare another method, like
init()
. It’s still possible, of course, for
you to define constructors for your servlets, but in the constructor
you don’t have access to the ServletConfig
object or the ability to throw ...
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