Struts2 Result, Thread safety, and Action Context?

Question

In Struts2

• actions are thread safe and each request initiate a separate action class object.
• Interceptors are not thread safe as only on object is initiated for all requests. They receive ActionInvocation object in their execute() method and can access action context using this object. Please see "Are Interceptors in Struts2 Thread UNsafe?"

Keeping these things in mind, I believed that

• Results are not thread safe as they receive ActionInvocation object in their execute() method.

I found following line of code in book "Manning Struts2 in Action" while creating a custom result class.

ServletActionContext.getResponse()

I am confused why author did not get response using actionInvocation object i.e.

actionInvocation.getInvocationContext().get(StrutsStatics.HTTP_RESPONSE);

Now I have following questions in my mind.

• Are Results thread safe?
• If Result are not thread safe and there are two different requests, how ServletActionContext returns relevant response?

Answer 1

Contexts use ThreadLocals.

Results are clearly instantiated per-request--look at something simple, like StreamResult: it uses instance variables for things like contentType and so on.