1. Struts Framework
ExecuteAndWait Interceptor
Introduction
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execAndWait
 The ExecuteAndWaitInterceptor is used for running long-lived
actions in the background while showing the user a
progress meter(loader image using JavaScript) .
 This also prevents the HTTP request from timing out when
the action takes more than 5 or 10 minutes.

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execAndWait
 Using this interceptor is pretty straight forward.
 Assuming that you are including struts-default.xml, and this
interceptor is already configured but is not part of any of the
default stacks then it wont work.
 Because of the nature of this interceptor, it must be
the last interceptor in the stack.

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execAndWait
 This interceptor works on a per-session basis.
 It means, same action name ( DemoAction.class ) cannot be
run more than once at a time in a given session. On the
initial request or any subsequent requests (before the action
has completed), the wait result will be returned.
 The wait result is responsible for issuing a subsequent
request back to the action, giving the effect of a self-updating
progress meter.

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execAndWait
 If no "wait" result is found, Struts will automatically
generate a wait result on the fly.
 But this result is written in FreeMarker and cannot run
unless FreeMarker is installed.
 If you don't want to use it with FreeMarker then must
provide a wait page as a result.

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execAndWait
 Whenever the wait result is returned, the action that is
currently running in the background will be placed on top of
the stack.
 This allows you to display progress data, such as a count, in
the wait page. By making the wait page automatically reload
the request to the action (which will be short-circuited by
the interceptor), can give the appearance of an automatic
progress meter.

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execAndWait
 Whenever the wait result is returned, the action that is
currently running in the background will be placed on top of
the stack.
 This allows you to display progress data, such as a count, in
the wait page. By making the wait page automatically reload
the request to the action (which will be short-circuited by
the interceptor), can give the appearance of an automatic
progress meter.

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execAndWait
 This interceptor also supports using an initial wait delay. An
initial delay is a time in milliseconds let the server wait
before the wait page is shown to the user.
 During the wait this interceptor will wake every 100 milii
second to check if the background process is done
premature, thus if the job for some reason doesn't take to
long the wait page is not shown to the user.

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execAndWait
 This is useful for e.g. search actions that have a wide span of
execution time. Using a delay time of 2000 millis we ensure
the user is presented fast search results immediately and for
the slow results a wait page is used.
 Important: Because the action will be running in a separate
thread, We can't use ActionContext because it is a
ThreadLocal.

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execAndWait
 The thread kicked off by this interceptor will be named in
the form actionNameBackgroundProcess.
 This means if we need to access session data, we need to
implement SessionAware rather than calling
ActionContext.getSession().

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execAndWait
 Parameters:threadPriority (optional) - the priority to
assign the thread. Default is Thread.NORM_PRIORITY.
 delay (optional) - an initial delay in millis to wait before the
wait page is shown (returning wait as result code). Default is
no initial delay.
 delaySleepInterval (optional) - only used with delay. Used
for waking up at certain intervals to check if the background
process is already done. Default is 100 millis.

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execAndWait
<action name=“abc" class="com.abc.DemoAction
<interceptor-ref name="execAndWait"/>
<result name="wait">wait.jsp</result>
<result name="success">success.jsp</result>
</action>

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