Re: [cinjug-users] tag handler reuse question

["Mike Ball" <mwball@xxxxxxxxx>]

Tag handler pooling/reuse is implemented differently in many
containers.  For example Websphere has a few strategies you can choose
from like thread level, page level, etc.

If you are using pooling/reuse it is best practice to get your tag
back to it's original state before it is returned to the pool.  But in
Websphere the release() method is not called before the tag is reused,
it is called at the end of the page/request/whatever, but the doEndTag
is always called.

I don't know if Weblogic supports tag pooling/reuse, but Tomcat does
as well as some other servlet containers.  It's probably in your best
interest to have the release and doEndTag methods implemented to
ensure that the tag is returned to it's original state so your
application can take advantage of whatever optimization the container
provides.



On 3/27/07, Mitchell, John <jlmitchell@xxxxxxxx> wrote:
> I just noticed some code in a doEndTag() which raised my eyebrows.
>
> In J2EE, I understand that the container (implementation of the spec) can
> pool session beans, and that this is configurable.  ...likewise with
> connection pools.
>
> Everything else I had thought was either...(1) a static class (rather,
> static methods in a class) which would have application scope (more than one
> session can affect the same attributes, raising some coding considerations),
> or...(2) an instance of a class, having - at the most - session scope via a
> reference put in the session (unless explicitly given a reference in the
> application scope).
>
> The following code implies that the container (weblogic, in my case) might
> decide to keep a tag handler instance for reuse by other sessions, or at
> least by my session once again (not sure if the former).
>
> If the former, that would seem to put the responsibility on the developer to
> 'clean up' or null-out attributes before being done, and even synchronize
> the scope from doStartTag() through doEndTag().  If the later, puts the same
> responsibility on the developer (apparently), but of course there is no
> concurrence concern.
>
> Any input on this?  I had never heard of this before.  (...assuming the
> logic was placed there by someone correctly understanding the container
> capability/discretion to reuse an instance...)
>
> Thanks,
>
> John Mitchell
>
>   public int doEndTag() throws JspException {
>     //reinit properties in case tag instance reused by container
>     crudOperation = null;
>     crudOperationBean = null;
>         [ ...etc. ]
>
> users@xxxxxxxxxx
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