org.apache.struts2.interceptor
Class ExecuteAndWaitInterceptor

java.lang.Object
  com.opensymphony.xwork2.interceptor.AbstractInterceptor
      com.opensymphony.xwork2.interceptor.MethodFilterInterceptor
          org.apache.struts2.interceptor.ExecuteAndWaitInterceptor

All Implemented Interfaces:

Interceptor, Serializable

public class ExecuteAndWaitInterceptor
extends 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.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:

Serialized Form

Field Summary

protected int	delay
protected int	delaySleepInterval
protected boolean	executeAfterValidationPass
static String	KEY
private static Logger	LOG
private static long	serialVersionUID
private int	threadPriority
static String	WAIT

Fields inherited from class com.opensymphony.xwork2.interceptor.MethodFilterInterceptor

excludeMethods, includeMethods, log

Constructor Summary

ExecuteAndWaitInterceptor()

Method Summary

void	destroy() Does nothing
protected String	doIntercept(ActionInvocation actionInvocation) Subclasses must override to implement the interceptor logic.
protected String	getBackgroundProcessName(ActionProxy proxy) Returns the name to associate the background process.
protected BackgroundProcess	getNewBackgroundProcess(String name, ActionInvocation actionInvocation, int threadPriority) Creates a new background process
void	init() Does nothing
protected void	performInitialDelay(BackgroundProcess bp) Performs the initial delay.
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 not
void	setThreadPriority(int threadPriority) Sets the thread priority of the background process.

Methods inherited from class com.opensymphony.xwork2.interceptor.MethodFilterInterceptor

applyInterceptor, getExcludeMethodsSet, getIncludeMethodsSet, intercept, setExcludeMethods, setIncludeMethods

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

serialVersionUID

private static final long serialVersionUID

See Also:

Constant Field Values

LOG

private static final Logger LOG

KEY

public static final String KEY

See Also:

Constant Field Values

WAIT

public static final String WAIT

See Also:

Constant Field Values

delay

protected int delay

delaySleepInterval

protected int delaySleepInterval

executeAfterValidationPass

protected boolean executeAfterValidationPass

threadPriority

private int threadPriority

Constructor Detail

ExecuteAndWaitInterceptor

public ExecuteAndWaitInterceptor()

Method Detail

init

public void init()

Description copied from class: AbstractInterceptor

Does nothing

Specified by:

init in interface Interceptor

Overrides:

init in class AbstractInterceptor

getNewBackgroundProcess

protected BackgroundProcess getNewBackgroundProcess(String name,
                                                    ActionInvocation actionInvocation,
                                                    int threadPriority)

Creates a new background process

Parameters:

name - The process name

actionInvocation - The action invocation

threadPriority - The thread priority

Returns:

The new process

getBackgroundProcessName

protected String getBackgroundProcessName(ActionProxy proxy)

Returns the name to associate the background process. Override to change the way background processes are mapped to requests.

Returns:

the name of the background thread

doIntercept

protected String doIntercept(ActionInvocation actionInvocation)
                      throws Exception

Description copied from class: MethodFilterInterceptor

Subclasses must override to implement the interceptor logic.

Specified by:

doIntercept in class MethodFilterInterceptor

Parameters:

actionInvocation - the action invocation

Returns:

the result of invocation

Throws:

Exception

destroy

public void destroy()

Description copied from class: AbstractInterceptor

Does nothing

Specified by:

destroy in interface Interceptor

Overrides:

destroy in class AbstractInterceptor

performInitialDelay

protected void performInitialDelay(BackgroundProcess bp)
                            throws InterruptedException

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.

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 from Thread.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