This looked like an interesting problem, and I already had most of the pieces in place, so here's my first attempt, which is implemented in a single class (also attached, along with some test files):
http://code.google.com/p/gaevfs/source/browse/trunk/src/com/newatlanta/appengine/taskqueue/Deferred.java
I'm more than happy to contribute this for inclusion in the SDK.
Some caveats:
1) Because of issue #2097
(http://code.google.com/p/googleappengine/issues/detail?id=2097), this
doesn't work on the development server (it does work in production).
So go star that issue!
2) I've only done minimal testing on the production server (see the
attached test files).
3) This post is the only documentation that's currently available.
First, add the following your your web.xml:
<servlet>
<servlet-name>Deferred</servlet-name>
<servlet-class>com.newatlanta.appengine.taskqueue.Deferred</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>Deferred</servlet-name>
<url-pattern>/_ah/queue/deferred</url-pattern>
</servlet-mapping>
Second, define the "deferred" queue within queue.xml (use whatever
rate you want):
<queue>
<name>deferred</name>
<rate>10/s</rate>
</queue>
Next, create a class that implements the
com.newatlanta.appengine.taskqueue.Deferred.Deferrable interface; the
"doTask()" method of this class is where you implement your task
logic.
Then, invoke the com.newatlanta.appengine.taskqueue.Deferred.defer()
method to queue up your task:
TestDeferred testDeferred = new TestDeferred(); // implements Deferrable
Deferred.defer( testDeferred, "one", "two", "three", 1, 2, 3 );
(Note that it would be possible to pass arguments as attributes to
your Deferrable instance, rather than using varargs; I'm not sure it
makes much difference which you choose).
Just as for the Python implementation, if the arguments size exceeds
10KB, the arguments are stored in a datastore entity, which is then
deleted when the task is executed. Also, your doTask() method can
throw a PermanentTaskFailure exception to halt retries; any other
exceptions cause the task to be retried.
Let me know if you find this useful, have any questions or encounter
any problems.
Vince
On Fri, Oct 30, 2009 at 6:13 PM, Jason (Google) <[email protected]> wrote:
> Hi David. This may be coming to Java eventually, but it hasn't been started
> yet. If you or anyone else is interested in contributing, let me know.
>
> - Jason
>
> On Wed, Oct 28, 2009 at 7:52 AM, David Chandler <[email protected]>
> wrote:
>>
>> Re: http://code.google.com/appengine/articles/deferred.html
>>
>> Will this be coming to AppEngine for Java?
>>
>> David Chandler
>> http://turbomanage.wordpress.com
>>
>>
>
>
> >
>
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TestDeferred.java
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testDeferred.jsp
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Deferred.java
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