THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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Camel supports implementing the Polling Consumer from the EIP patterns using the PollingConsumer interface which can be created via the Endpoint.createPollingConsumer() method.
So in your Java code you can do
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There are 3 main polling methods on PollingConsumer
Method name | Description |
|---|---|
Waits until a message is available and then returns it; potentially blocking forever | |
Attempts to receive a message exchange, waiting up to the given timeout and returning null if no message exchange could be received within the time available | |
Attempts to receive a message exchange immediately without waiting and returning null if a message exchange is not available yet |
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Since this a such a common pattern, polling components can extend the ScheduledPollConsumer base class which makes it simpler to implement this pattern.
There is also the Quartz Component which provides scheduled delivery of messages using the Quartz enterprise scheduler.
For more details see:
- PollingConsumer
- Scheduled Polling Components
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About error handling and scheduled polling consumers
ScheduledPollConsumer is scheduled based and its run method is invoked periodically based on schedule settings. But errors can also occur when a poll being executed. For instance if Camel should poll a file network, and this network resource is not available then a java.io.IOException could occur. As this error happens before any Exchange has been created and prepared for routing, then the regular Error handling in Camel does not apply. So what does the consumer do then? Well the exception is propagated back to the run method where its handled. Camel will by default log the exception at WARN level and then ignore it. At next schedule the error could have been resolved and thus being able to poll the endpoint successfully.
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