Poll

Camel supports the Content Enricher from the EIP patterns .

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In Camel the Content Enricher can be done in several ways:

The Poll EIP is a simplified Poll Enrich which only supports:

  • Static Endpoints

  • No custom aggregation or other advanced features

  • Uses a 20 seconds timeout (default)

Options

The Poll eip supports the following options which are listed below.

Name Description Default Type

note

The note for this node.

String

description

The description for this node.

String

disabled

Whether to disable this EIP from the route during build time. Once an EIP has been disabled then it cannot be enabled later at runtime.

false

Boolean

variableReceive

To use a variable to store the received message body (only body, not headers). This makes it handy to use variables for user data and to easily control what data to use for sending and receiving.

String

uri

Required The uri of the endpoint to poll a single message from. The result is stored in the original message body (or in a variable if variableReceive is set).

String

timeout

Timeout in millis when polling from the external service. The default value is 20000 (20 seconds).

20000

String

Exchange properties

The Poll eip has no exchange properties.

Polling a message using Poll EIP

poll uses a Polling Consumer to obtain the data. It is usually used for Event Message messaging, for instance, to read a file or download a file using FTP.

We have three methods when polling:

  • receive : Waits until a message is available and then returns it. Warning that this method could block indefinitely if no messages are available.

  • receiveNoWait : Attempts to receive a message exchange immediately without waiting and returning null if a message exchange is not available yet.

  • receive(timeout) : Attempts to receive a message exchange, waiting up to the given timeout to expire if a message is not yet available. Returns the message or null if the timeout expired.

Timeout

By default, Camel will use the receive(timeout) which has a 20 seconds timeout.

You can pass in a timeout value that determines which method to use:

  • if timeout is -1 or other negative number then receive is selected ( Important: the receive method may block if there is no message)

  • if timeout is 0 then receiveNoWait is selected

  • otherwise, receive(timeout) is selected

The timeout values are in milliseconds.

Using Poll

For example to download an FTP file:

  • Java

  • XML

  • YAML 

from("direct:payload")
  .poll("ftp:myserver.com/myfolder?fileName=report-file.pdf");
<route>
    <from uri="direct:payload"/>
    <poll uri="ftp:myserver.com/myfolder?fileName=report-file.pdf"/>
</route>
- route:
    from:
      uri: direct:payload
      steps:
        - poll:
            uri: ftp:myserver.com/myfolder
            parameters:
              fileName: report-file.pdf
You can use dynamic values using the simple language in the uri, as shown below:

  • Java

  • XML

  • YAML 

from("direct:payload")
  .poll("ftp:myserver.com/myfolder?fileName=report-${header.id}.pdf");
<route>
    <from uri="direct:payload"/>
    <poll uri="ftp:myserver.com/myfolder?fileName=report-${header.id}.pdf"/>
</route>
- route:
    from:
      uri: direct:payload
      steps:
        - poll:
            uri: ftp:myserver.com/myfolder
            parameters:
              fileName: "report-${header.id}.pdf"

Using Poll with Rest DSL

You can also use poll with Rest DSL to, for example, download a file from AWS S3 as the response of an API call.

  • Java

  • XML

  • YAML 

rest("/report")
  .get("/{id}/payload")
    .to*("direct:payload");

from("direct:payload")
  .poll("aws-s3:xavier-dev?amazonS3Client=#s3client&amp;deleteAfterRead=false&amp;fileName=report-file.pdf")
<rest path="/report" desription="Report REST API">
    <get path="/{id}/payload">
        <to uri="direct:payload"/>
    </get>
</rest>

<route>
    <from uri="direct:payload"/>
    <poll uri="aws-s3:xavier-dev?amazonS3Client=#s3client&amp;deleteAfterRead=false&amp;fileName=report-file.pdf"/>
</route>
- rest:
    path: /report
    get:
      - path: /{id}/payload
        to:
          uri: direct:payload
- route:
    from:
      uri: direct:payload
      steps:
        - poll:
            uri: aws-s3:xavier-dev
            parameters:
              amazonS3Client: "#s3client"
              deleteAfterRead: false
              fileName: report-file.pdf

Using Poll with file based components

When using poll or pollEnrich with the file based components, then the eagerLimitMaxMessagesPerPoll option has changed default from false to true from Camel 4.13 onwards. Only use-cases where you need to sort the files first, requires to explicit set the option eagerLimitMaxMessagesPerPoll=false to make Camel scan for all files first before sorting, and then poll or pollEnrich will then pick the top file after the sorting.

This improves performance for use-cases without need for sorting first.

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