ExecuteAndWaitInterceptorpublic class ExecuteAndWaitInterceptor extends com.opensymphony.xwork2.interceptor.MethodFilterInterceptor
The ExecuteAndWaitInterceptor is great for running long-lived actions in the background while showing the user a nice
progress meter. This also prevents the HTTP request from timing out when the action takes more than 5 or 10 minutes.
Using this interceptor is pretty straight forward. Assuming that you are including struts-default.xml, this
interceptor is already configured but is not part of any of the default stacks. Because of the nature of this
interceptor, it must be the last interceptor in the stack.
This interceptor works on a per-session basis. That means that the same action name (myLongRunningAction, in the
above example) 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.
If no "wait" result is found, Struts will automatically generate a wait result on the fly. This result is
written in FreeMarker and cannot run unless FreeMarker is installed. If you don't wish to deploy with FreeMarker, you
must provide your own wait result. This is generally a good thing to do anyway, as the default wait page is very
plain.
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), you can give
the appearance of an automatic progress meter.
This interceptor also supports using an initial wait delay. An initial delay is a time in milliseconds we let the
server wait before the wait page is shown to the user. During the wait this interceptor will wake every 100 millis
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.
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 seperate thread, you can't use ActionContext because it
is a ThreadLocal. This means if you need to access, for example, session data, you need to implement SessionAware
rather than calling ActionContext.getSesion().
The thread kicked off by this interceptor will be named in the form actionNameBrackgroundProcess.
For example, the search action would run as a thread named searchBackgroundProcess.
Interceptor 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.
Extending the interceptor:
If you wish to make special preparations before and/or after the invocation of the background thread, you can extend
the BackgroundProcess class and implement the beforeInvocation() and afterInvocation() methods. This may be useful
for obtaining and releasing resources that the background process will need to execute successfully. To use your
background process extension, extend ExecuteAndWaitInterceptor and implement the getNewBackgroundProcess() method.
Example code:
<action name="someAction" class="com.examples.SomeAction">
<interceptor-ref name="completeStack"/>
<interceptor-ref name="execAndWait"/>
<result name="wait">longRunningAction-wait.jsp</result>
<result name="success">longRunningAction-success.jsp</result>
</action>
<%@ taglib prefix="s" uri="/struts" %>
<html>
<head>
<title>Please wait</title>
<meta http-equiv="refresh" content="5;url=<a:url includeParams="all" />"/>
</head>
<body>
Please wait while we process your request.
Click <a href="<a:url includeParams="all" />"></a> if this page does not reload automatically.
</body>
</html>
Example code2:
This example will wait 2 second (2000 millis) before the wait page is shown to the user. Therefore
if the long process didn't last long anyway the user isn't shown a wait page.
<action name="someAction" class="com.examples.SomeAction">
<interceptor-ref name="completeStack"/>
<interceptor-ref name="execAndWait">
<param name="delay">2000<param>
<interceptor-ref>
<result name="wait">longRunningAction-wait.jsp</result>
<result name="success">longRunningAction-success.jsp</result>
</action>
Example code3:
This example will wait 1 second (1000 millis) before the wait page is shown to the user.
And at every 50 millis this interceptor will check if the background process is done, if so
it will return before the 1 second has elapsed, and the user isn't shown a wait page.
<action name="someAction" class="com.examples.SomeAction">
<interceptor-ref name="completeStack"/>
<interceptor-ref name="execAndWait">
<param name="delay">1000<param>
<param name="delaySleepInterval">50<param>
<interceptor-ref>
<result name="wait">longRunningAction-wait.jsp</result>
<result name="success">longRunningAction-success.jsp</result>
</action>
|
| Fields Summary |
|---|
| private static final long | serialVersionUID | | private static final Log | LOG | | public static final String | KEY | | public static final String | WAIT | | protected int | delay | | protected int | delaySleepInterval | | protected boolean | executeAfterValidationPass | | private int | threadPriority |
| Methods Summary |
|---|
| public void | destroy()
| | protected java.lang.String | doIntercept(com.opensymphony.xwork2.ActionInvocation actionInvocation)
ActionProxy proxy = actionInvocation.getProxy();
String name = getBackgroundProcessName(proxy);
ActionContext context = actionInvocation.getInvocationContext();
Map session = context.getSession();
Boolean secondTime = true;
if (executeAfterValidationPass) {
secondTime = (Boolean) context.get(KEY);
if (secondTime == null) {
context.put(KEY, true);
secondTime = false;
} else {
secondTime = true;
context.put(KEY, null);
}
}
synchronized (session) {
BackgroundProcess bp = (BackgroundProcess) session.get(KEY + name);
if ((!executeAfterValidationPass || secondTime) && bp == null) {
bp = getNewBackgroundProcess(name, actionInvocation, threadPriority);
session.put(KEY + name, bp);
performInitialDelay(bp); // first time let some time pass before showing wait page
secondTime = false;
}
if ((!executeAfterValidationPass || !secondTime) && bp != null && !bp.isDone()) {
actionInvocation.getStack().push(bp.getAction());
Map results = proxy.getConfig().getResults();
if (!results.containsKey(WAIT)) {
LOG.warn("ExecuteAndWait interceptor has detected that no result named 'wait' is available. " +
"Defaulting to a plain built-in wait page. It is highly recommend you " +
"provide an action-specific or global result named '" + WAIT +
"'! This requires FreeMarker support and won't work if you don't have it installed");
// no wait result? hmm -- let's try to do dynamically put it in for you!
ResultConfig rc = new ResultConfig(WAIT, "org.apache.struts2.views.freemarker.FreemarkerResult",
Collections.singletonMap("location", "/org/apache/struts2/interceptor/wait.ftl"));
results.put(WAIT, rc);
}
return WAIT;
} else if ((!executeAfterValidationPass || !secondTime) && bp != null && bp.isDone()) {
session.remove(KEY + name);
actionInvocation.getStack().push(bp.getAction());
// if an exception occured during action execution, throw it here
if (bp.getException() != null) {
throw bp.getException();
}
return bp.getResult();
} else {
// this is the first instance of the interceptor and there is no existing action
// already run in the background, so let's just let this pass through. We assume
// the action invocation will be run in the background on the subsequent pass through
// this interceptor
return actionInvocation.invoke();
}
}
| | protected java.lang.String | getBackgroundProcessName(com.opensymphony.xwork2.ActionProxy proxy)Returns the name to associate the background process. Override to change the way background processes
are mapped to requests.
return proxy.getActionName();
| | protected BackgroundProcess | getNewBackgroundProcess(java.lang.String name, com.opensymphony.xwork2.ActionInvocation actionInvocation, int threadPriority)Creates a new background process
return new BackgroundProcess(name + "BackgroundThread", actionInvocation, threadPriority);
| | public void | init()
/* (non-Javadoc)
* @see com.opensymphony.xwork2.interceptor.Interceptor#init()
*/
| | protected void | performInitialDelay(BackgroundProcess bp)Performs the initial delay.
When this interceptor is executed for the first time this methods handles any provided initial delay.
An initial delay is a time in miliseconds we let the server wait before we continue.
During the wait this interceptor will wake every 100 millis 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.
if (delay <= 0 || delaySleepInterval <= 0) {
return;
}
int steps = delay / delaySleepInterval;
if (LOG.isDebugEnabled()) {
LOG.debug("Delaying for " + delay + " millis. (using " + steps + " steps)");
}
int step;
for (step = 0; step < steps && !bp.isDone(); step++) {
Thread.sleep(delaySleepInterval);
}
if (LOG.isDebugEnabled()) {
LOG.debug("Sleeping ended after " + step + " steps and the background process is " + (bp.isDone() ? " done" : " not done"));
}
| | public void | setDelay(int delay)Sets the initial delay in millis (msec).
this.delay = delay;
| | public void | setDelaySleepInterval(int delaySleepInterval)Sets the sleep interval in millis (msec) when performing the initial delay.
this.delaySleepInterval = delaySleepInterval;
| | public void | setExecuteAfterValidationPass(boolean executeAfterValidationPass)Whether to start the background process after the second pass (first being validation)
or not
this.executeAfterValidationPass = executeAfterValidationPass;
| | public void | setThreadPriority(int threadPriority)Sets the thread priority of the background process.
this.threadPriority = threadPriority;
|
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