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 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:
    Serialized Form

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected int` | `delay`
    `protected int` | `delaySleepInterval`
    `protected boolean` | `executeAfterValidationPass`
    `static String` | `KEY`
    `static String` | `WAIT`

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

      `excludeMethods, includeMethods`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `ExecuteAndWaitInterceptor()`

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `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
    `protected void` | `performInitialDelay(BackgroundProcess bp)` 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 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 com.opensymphony.xwork2.interceptor.AbstractInterceptor

      `destroy, init`

    - ### Methods inherited from class java.lang.Object

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

- - ### Field Detail

    - #### 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

  - ### Constructor Detail

    - #### ExecuteAndWaitInterceptor

          public ExecuteAndWaitInterceptor()

  - ### Method Detail

    - #### setContainer

          public void setContainer(Container container)

    - #### 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.
      Parameters:
        `proxy` - action proxy
      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` - in case of any errors

    - #### 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 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 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

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