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51.7. gtask

gtask Component
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The gtask component contributes to the Camel Components for Google App Engine (GAE). It supports asynchronous message processing on GAE by using the task queueing service as message queue. For adding messages to a queue it uses the task queue API. For receiving messages from a queue it installs an HTTP callback handler. The handler is called by an HTTP POST callback (a web hook) initiated by the task queueing service. Whenever a new task is added to a queue a callback will be sent. The gtask component abstracts from these details and supports endpoint URIs that make message queueing on GAE as easy as message queueing with JMS or SEDA.

URI format
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gtask://queue-name
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Options
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Expand
Name Default Value Context Description
workerRoot worker Producer The servlet mapping for callback handlers. By default, this component requires a callback servlet mapping of /worker/*. If another servlet mapping is used e.g. /myworker/* it must be set as option on the producer side: to("gtask:myqueue?workerRoot=myworker").
inboundBindingRef reference to GTaskBinding Consumer Reference to an InboundBinding<GTaskEndpoint, HttpServletRequest, HttpServletResponse> in the Registry for customizing the binding of an Exchange to the Servlet API. The referenced binding is used as post-processor to org.apache.camel.component.http.HttpBinding.
outboundBindingRef reference to GTaskBinding Producer Reference to an OutboundBinding<GTaskEndpoint, TaskOptions, void> in the Registry for customizing the binding of an Exchange to the task queueing service.
On the consumer-side, all options of the Servlet component are supported.

Message headers
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On the consumer-side all headers of the Servlet component component are supported plus the following.
Expand
Name Type Context Description
GTaskBinding.GTASK_QUEUE_NAME String Consumer Name of the task queue.
GTaskBinding.GTASK_TASK_NAME String Consumer Name of the task (generated value).
GTaskBinding.GTASK_RETRY_COUNT int Consumer Number of callback retries.

Message body
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On the producer side the in message body is converted to a byte[] and is POSTed to the callback handler as content-type application/octet-stream.

Usage
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Setting up tasks queues is an administrative task on Google App Engine. Only one queue is pre-configured and can be referenced by name out-of-the-box: the default queue. This queue will be used in the following examples. Please note that when using task queues on the local development server, tasks must be executed manually from the developer console.

Default queue
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...
.to(gtask:default) // add message to default queue

from(gtask:default) // receive message from default queue (via a web hook)
...
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This example requires the following servlet mapping.
web.xml
    ...
    <servlet>
        <servlet-name>CamelServlet</servlet-name>
        <servlet-class>org.apache.camel.component.servlet.CamelHttpTransportServlet</servlet-class>
        ...
    </servlet>
    ...
    <servlet-mapping>
        <servlet-name>CamelServlet</servlet-name>
        <url-pattern>/worker/*</url-pattern>
    </servlet-mapping>
    ...
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Dependencies
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Maven users will need to add the following dependency to their pom.xml.
pom.xml
<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-gae</artifactId>
    <version>${camel-version}</version>
</dependency>
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where ${camel-version} must be replaced by the actual version of Apache Camel (2.1.0 or higher).
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