CODEWITHSUNDEEP
javagoogle-app-enginetask-queue
Katedral Pillon
Katedral Pillon

Reputation: 14844

Use POJO in app engine Task Queue

Is it possible to use POJOs in App-Engine Task Queues? Or must the values always be String?

Queue queue = QueueFactory.getQueue("my_queue");
queue.add(withUrl("/my_worker").param("my_key", obj));

What if my POJO is complex, such that one of the fields in the POJO is an ArrayList?

Upvotes: 1

Views: 681

Answers (2)

Deviling Master
Deviling Master

Reputation: 3113

You can use a deferred task which is an object launched on a queue like a regular task. Basically, it is a different Thread which is launched through the TaskQueue options and you can pass a serializable object instead of plain http parameters.

https://cloud.google.com/appengine/docs/java/taskqueue/overview-push#Java_Deferred_tasks

While the DeferredTask API is a convenient way to handle serialization

You need to create a class which extends DeferredTask (which has a constructor receiving your POJO).

public class MyDeferredTask implements DeferredTask {

    private MyPojo pojo;

    public MyDeferredTask(MyPojo pojo) {
        this.pojo = pojo;
    }

    @Override
    public void run() {
        // TODO Do stuff with pojo
    }
}

and then launch the task

MyDeferredTask task = new MyDeferredTask(pojo);
TaskOptions taskOptions = TaskOptions.Builder.withPayload(task);
TaskManager.getQueue("my-queue").add(taskOptions);

The good thing about this is that the if the payload is greater than 100kb, the POJO is automatically persisted on the datastore (up to 1 MB, as datastore entry limit) and then retrieved when your task starts.

Upvotes: 3

Alex Martelli
Alex Martelli

Reputation: 881575

TaskOptions' param method has two overloads: one takes a String, the other one takes a byte[]. POJOs implement java.io.Serializable, so you can serialize one to a byte[] as shown e.g at Java Serializable Object to Byte Array (and upon reception deserialize the byte[] back).

The maximum task size, per https://cloud.google.com/appengine/docs/python/taskqueue/overview-push#Python_Quotas_and_limits_for_push_queues , is 100 KB (so the max size of the byte[] payload will have to be somewhat less than that). If that's a problem for you, you could consider stashing the POJO as an entity in the datastore and just sending the corresponding key...

Upvotes: 3

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