Is Struts ThreadSafe

[Rajendra Prakash]

My interviewer asked , is struts Threadsafe(Is struts Action class thread safe ) . In google am getting different answers.
1. "No Struts is not thread safe " 2. Struts is not only thread-safe but also thread-dependent.
can you give me correct answer with reason.

[Rajendra Prakash]

How to implement Threadsafe and singleton concepts in struts. Is it default or should we implement externally.

[Ulf Dittmer]

Struts is a big framework, and the question of whether or not it's thread-safe can mean different things.

Struts Actions are thread-safe in Struts 2, and NOT thread-safe in Struts 1 unless you make them so (at least that's how I read http://struts.apache.org/2.0.14/docs/comparing-struts-1-and-2.html).

But even Struts 2 is a Java web app, and thus based on objects that are not inherently thread-safe (like HttpSession and ServletContext), so it's perfectly possible to create thread-unsafe web apps using Struts 2. Your code needs to take appropriate measures to guard against any concurrency issues when those are involved.

I generally recommend getting a good book on Java concurrency (the ones by Oaks/Wong and Doug Lea in particular); they're really indispensible for getting a good grounding in the issues and solutions Java provides.

[Ram Charan]

That's true. Struts1 action classes are not thread safe. You have to write thread safe action classes(Have only constants as instance variables).

[Ulf Dittmer]

You have to write thread safe action classes (Have only constants as instance variables).

While that approach is sufficient for achieving thread-safety, it's not a necessary. The crucial aspect is that access to shared mutable state must be guarded. There's nothing wrong with using instance variable in servlets or Struts 1 actions, as long as they are read-only, or access to them is properly synchronized.

Note that there are other potential sources of concurrency problems besides instance variables, like sessions and context attributes.

[David Newton]

This is one of those interview questions where I end up asking the interviewer more questions than s/he asked me in order to be able to actually answer their original question, because as asked, it's a little misleading. They may just be looking for the canonical answer, which in general, makes me not want to work for them.