Class ExecuteAndWaitInterceptor
- All Implemented Interfaces:
Serializable
,ConditionalInterceptor
,Interceptor
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 separate 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.getSession().
The thread kicked off by this interceptor will be named in the form actionNameBackgroundProcess. 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=<s:url includeParams="all" />"/> </head> <body> Please wait while we process your request. Click <a href="<s: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>
- See Also:
-
Field Summary
FieldsModifier and TypeFieldDescriptionprotected int
protected int
protected boolean
static final String
static final String
Fields inherited from class org.apache.struts2.interceptor.MethodFilterInterceptor
excludeMethods, includeMethods
-
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionvoid
destroy()
Does nothingprotected String
doIntercept
(ActionInvocation actionInvocation) Subclasses must override to implement the interceptor logic.protected String
Returns the name to associate the background process.protected BackgroundProcess
getNewBackgroundProcess
(String name, ActionInvocation actionInvocation, int threadPriority) Creates a new background processvoid
init()
Does nothingprotected void
Performs the initial delay.void
setContainer
(Container container) void
setDelay
(int delay) Sets the initial delay in millis (msec).void
setDelaySleepInterval
(int delaySleepInterval) Sets the sleep interval in millis (msec) when performing the initial delay.void
setExecuteAfterValidationPass
(boolean executeAfterValidationPass) Whether to start the background process after the second pass (first being validation) or notvoid
setExecutorProvider
(ExecutorProvider executorProvider) void
setThreadPriority
(int threadPriority) Sets the thread priority of the background process.Methods inherited from class org.apache.struts2.interceptor.MethodFilterInterceptor
applyInterceptor, getExcludeMethodsSet, getIncludeMethodsSet, intercept, setExcludeMethods, setIncludeMethods
Methods inherited from class org.apache.struts2.interceptor.AbstractInterceptor
setDisabled, shouldIntercept
-
Field Details
-
KEY
- See Also:
-
WAIT
- See Also:
-
delay
protected int delay -
delaySleepInterval
protected int delaySleepInterval -
executeAfterValidationPass
protected boolean executeAfterValidationPass
-
-
Constructor Details
-
ExecuteAndWaitInterceptor
public ExecuteAndWaitInterceptor()
-
-
Method Details
-
setContainer
-
setExecutorProvider
-
getNewBackgroundProcess
protected BackgroundProcess getNewBackgroundProcess(String name, ActionInvocation actionInvocation, int threadPriority) Creates a new background process- Parameters:
name
- The process nameactionInvocation
- The action invocationthreadPriority
- The thread priority- Returns:
- The new process
-
getBackgroundProcessName
Returns the name to associate the background process. Override to change the way background processes are mapped to requests.- Parameters:
proxy
- action proxy- Returns:
- the name of the background thread
-
doIntercept
Description copied from class:MethodFilterInterceptor
Subclasses must override to implement the interceptor logic.- Specified by:
doIntercept
in classMethodFilterInterceptor
- Parameters:
actionInvocation
- the action invocation- Returns:
- the result of invocation
- Throws:
Exception
- in case of any errors
-
performInitialDelay
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 milliseconds 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.- Parameters:
bp
- the background process- Throws:
InterruptedException
- is thrown by Thread.sleep
-
setThreadPriority
public void setThreadPriority(int threadPriority) Sets the thread priority of the background process.- Parameters:
threadPriority
- the priority fromThread.XXX
-
setDelay
public void setDelay(int delay) Sets the initial delay in millis (msec).- Parameters:
delay
- in millis. (0 for not used)
-
setDelaySleepInterval
public void setDelaySleepInterval(int delaySleepInterval) Sets the sleep interval in millis (msec) when performing the initial delay.- Parameters:
delaySleepInterval
- in millis (0 for not used)
-
setExecuteAfterValidationPass
public void setExecuteAfterValidationPass(boolean executeAfterValidationPass) Whether to start the background process after the second pass (first being validation) or not- Parameters:
executeAfterValidationPass
- the executeAfterValidationPass to set
-
init
public void init()Description copied from class:AbstractInterceptor
Does nothing- Specified by:
init
in interfaceInterceptor
- Overrides:
init
in classAbstractInterceptor
-
destroy
public void destroy()Description copied from class:AbstractInterceptor
Does nothing- Specified by:
destroy
in interfaceInterceptor
- Overrides:
destroy
in classAbstractInterceptor
-