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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.
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The isThreadSafe option marks a page as being thread-safe. By default, all JSPs are considered thread-safe. If you set the isThreadSafe option to false, the JSP engine makes sure that only one thread at a time is executing your JSP.
A thread-safe JSP/servlet is one that works correctly when more than one thread is running at the same time. To make your JSPs thread-safe, you can implement the SingleThreadModel interface that prevents two threads from accessing the service method at the same time.
Single Thread Model Interface was designed to guarantee that only one thread is executed at a time in a given servlet instance service method. It should be implemented to ensure that the servlet can handle only one request at a time. It is a marker interface and has no methods.
JSP (JavaServer Pages) is server side technology to create dynamic java web application. JSP can be thought as an extension to servlet technology because it provides features to easily create user views. JSP Page consists of HTML code and provide option to include java code for dynamic content.
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.
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