Between declaration tag and scriptlet which one is threadsafe?

[shankhas sanyal]

Hi all
recently i attended an interview and the interviewer asked me :
Between

 <%!=  %>  

declaration tag and

  <%  %>  

scriptlet tag which one is threadsafe? and why?


thanks for your help!

Shankha

[Abimaran Kugathasan]

If I asked, Where will those scriplets go in the generated servlet?

[Lester Burnham]

Both may be threadsafe, or both may not be threadsafe - it depends on what the code does.

[Abimaran Kugathasan]

Lester Burnham wrote:Both may be threadsafe, or both may not be threadsafe - it depends on what the code does.

How is it possible? Method local variable is Thread-Safe!?

[shankhas sanyal]

Abimaran Kugathasan wrote:If I asked, Where will those scriplets go in the generated servlet?

as i know the system generated servlet has 3 methods:

init()

_JspService()

and
destroy()

this is what i think, please correct me if i am wrong

inside the init() method the

  <%! %>  

declaration tag is declared.

inside the _JspService() method the scriptlet tag is declared.

my question now is: Is everything declared within the init() method threadsafe?

[Lester Burnham]

Abimaran Kugathasan wrote:How is it possible? Method local variable is Thread-Safe!?

Who's talking about method local variables? As I said, it depends on what the code does.

[Abimaran Kugathasan]

shankhas sanyal wrote:
inside the init() method the

  <%! %>  

declaration tag is declared.

inside the _JspService() method the scriptlet tag is declared.

my question now is: Is everything declared within the init() method threadsafe?

Declaration means, you are declaring it as a instance variable to that generated servlet. (It's also a Java Object!) And other thing, thread, which are created by the container for servicing won't access the init() method! It's there to initialize the servlet initialization parameters of the servlet, moreover it'll be invoked by the container.

[Abimaran Kugathasan]

Lester Burnham wrote:
Who's talking about method local variables? As I said, it depends on what the code does.

Where will the scriplets land in the generated servlet?

[Lester Burnham]

shankhas sanyal wrote:my question now is: Is everything declared within the init() method threadsafe?

Not necessarily. But the init method is not generally of concern when it comes to thread-safety - it is executed just once at a time when requests are not yet being accepted for the resulting servlet to be run.

But neither code in the declaration tag nor code in scriptlets ends up in the init method, so it doesn't hold the answer to what you were asked by the interviewer, nor does it answer what Abimaran asked you.

[Lester Burnham]

Abimaran Kugathasan wrote:

Lester Burnham wrote:
Who's talking about method local variables? As I said, it depends on what the code does.

Where will the scriplets land in the generated servlet?

I don't understand what this question has to do with the part of my post that you quoted.

[Abimaran Kugathasan]

Lester Burnham wrote:
I don't understand what this question has to do with the part of my post that you quoted.

If we declare a variable in scriptlets, then that will land in the service() method of the generated servlet. Then that will be a method local variable, and it's Thread-safe!

So that, I asked!

[Lester Burnham]

Abimaran Kugathasan wrote:If we declare a variable in scriptlets, then that will land in the service() method of the generated servlet. Then that will be a method local variable, and it's Thread-safe!

Again: Nobody is talking about declaring variables. If you look at the first post, you'll see that the place where the code would go is empty - so we don't know what it does. Maybe it does something threadsafe like using local variables; maybe it uses shared mutable state in a way that is not threadsafe - we simply don't know. Thread safety is not about where code lives, it's about what it does.

[Abimaran Kugathasan]

Lester Burnham wrote:
Again: Nobody is talking about declaring variables. If you look at the first post, you'll see that the place where the code would go is empty - so we don't know what it does. Maybe it does something threadsafe like using local variables; maybe it uses shared mutable state in a way that is not threadsafe - we simply don't know. Thread safety is not about where code lives, it's about what it does.

Yea! Correct! Thanks...

[Bear Bibeault]

But, of course, the most correct answer is "This isn't 2002, I'd never use either one in a modern JSP!"

[Abimaran Kugathasan]

Bear Bibeault wrote:But, of course, the most correct answer is "This isn't 2002, I'd never use either one in a modern JSP!"

Accept it Bear! But what is the usage of scriptlets in these days? Just curious to know! Thanks!