Question

I want to create a Thread safe JSP page. It is possible in Servlet by implementing SingleThreadModel interface but I don’t know how to do it in JSP page.

Answer 1

Theoretically, JSP pages can be indicated as threadsafe via the isThreadSafe page directive attribute. Setting a value of false, will get the container to synchronize access to page level objects (and not to session and application scoped objects or objects of any other variety). Obviously, it is still the responsibility of the developer to ensure that synchronous access to thread unsafe regions of code.

Morevoer, the SingleThreadModel interface has also been deprecated in the Servlet Specification release 2.4. The SingleThreadModel interface is used to implement the supposed thread safety in JSPs as well – generated servlet classes will implement the SingleThreadModel for JSPs that use the threadsafe attribute. The specification itself outlines why the interface is deprecated:

SRV.2.2.1 Note About The Single Thread Model

The use of the SingleThreadModel
interface guarantees that only one
thread at a time will execute in a
given servlet instance’s service
method. It is important to note that
this guarantee only applies to each
servlet instance, since the container
may choose to pool such objects.
Objects that are accessible to more
than one servlet instance at a time,
such as instances of HttpSession, may
be available at any particular time to
multiple servlets, including those
that implement SingleThreadModel.

It is recommended that a developer
take other means to resolve those
issues instead of implementing this
interface, such as avoiding the usage
of an instance variable or
synchronizing the block of the code
accessing those resources. The
SingleThreadModel Interface is
deprecated in this version of the
specification.