java - role of multithreading in web application

Question

I am using java(Servlets, JSPs) since 2 years for web application development. In those 2 years I never required to use multithreading(explicitly - as I know that servlet containers uses threading to serve same servlet to different requests) in any project.

But whenever I attend an interview for Web Developer position(java), then there are several questions related to threads in java. I know the basics of java threading so answering the questions is not a problem. But sometimes I get confused whether I am missing something while developing web application by not using mutithreading?

So my question is that what is the role of multithreading in Web Application? Any example where multithreading can be used in web application will be appreciated.

Thanks in advance.

Answer 1

Multi-threading can be used in Web Apps mainly when you are interested in asynchronous calls.

Consider for example you have a Web application that activates a user's state on a GSM network (e.g activate 4G plan) and sends a confirmatory SMS or email message at the end.

Knowing that the Web call would take several minutes - especially if the GSM network is stressed - it does not make sense to call it directly from the Web thread.

So basically, when a user clicks "Activate", the Server returns something like "Thanks for activating the 4G plan. Your plan will be activated in a few minutes and you will receive a confirmation SMS/email".

In that case, you server has to spawn a new thread, ideally using a thread pool, in an asynchronous manner, and immediately return a response to the user.

Workflow:

1- User clicks "Activate" button
2- Servlet receives request and activates a new "Activate 4G Plan" task in a thread pool.
3- Servlet immediately returns an HTML response to the user without waiting for the task to be finalized.
4- End of Http transaction
. . .

Asynchronously, the 4G plan gets activated later and the user gets notified through SMS or email, etc...