Routing Slip

Camel supports the Routing Slip from the EIP patterns.

How do we route a message consecutively through a series of processing steps when the sequence of steps is not known at design-time and may vary for each message?

image

Attach a Routing Slip to each message, specifying the sequence of processing steps. Wrap each component with a special message router that reads the Routing Slip and routes the message to the next component in the list.

Options

The Routing Slip eip supports 2 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

expression

Required The expression to compute the routing slip of endpoint URIs. The result is a delimited list of endpoint URIs that defines the series of processing steps.

ExpressionDefinition

uriDelimiter

The delimiter used to separate endpoint URIs in the routing slip expression. Default is comma.

,

String

ignoreInvalidEndpoints

If enabled then invalid endpoint URIs are ignored and logged instead of throwing an exception.

false

Boolean

cacheSize

Configures the cache size for ProducerCache which caches producers for reuse. The default cache size is 1000. Set to -1 to turn off caching.

Integer
See the cacheSize option for more details on how much cache to use depending on how many or few unique endpoints are used.

Exchange properties

The Routing Slip eip supports 2 exchange properties, which are listed below.

The exchange properties are set on the Exchange by the EIP, unless otherwise specified in the description. This means those properties are available after this EIP has completed processing the Exchange.

Name Description Default Type

CamelSlipEndpoint

The endpoint uri of this routing slip.

String

CamelToEndpoint

Endpoint URI where this Exchange is being sent to.

String

Using Routing Slip

The Routing Slip EIP allows to route a message through a series of endpoints (the slip).

There can be 1 or more endpoint uris in the slip.

A slip can be empty, meaning that the message will not be routed anywhere.

The following route will take any messages sent to the Apache ActiveMQ queue cheese and use the header with key "whereTo" that is used to compute the slip (endpoint uris).

  • Java

  • XML

  • YAML

from("activemq:cheese")
  .routingSlip(header("whereTo"));
<route>
  <from uri="activemq:cheese"/>
  <routingSlip>
    <header>whereTo</header>
  </routingSlip>
</route>
- route:
    from:
      uri: activemq:cheese
      steps:
        - routingSlip:
            expression:
              header:
                expression: whereTo

The value of the header ("whereTo") should be a comma-delimited string of endpoint URIs you wish the message to be routed to. The message will be routed in a pipeline fashion, i.e., one after the other.

The Routing Slip sets a property, Exchange.SLIP_ENDPOINT, on the Exchange which contains the current endpoint as it advanced though the slip. This allows you to know how far we have processed in the slip.

The Routing Slip will compute the slip beforehand, which means the slip is only computed once. If you need to compute the slip on-the-fly, then use the Dynamic Router EIP instead.

How is the slip computed

The Routing Slip uses an Expression to compute the value for the slip. The result of the expression can be one of:

  • String

  • Collection

  • Iterator or Iterable

  • Array

If the value is a String then the uriDelimiter is used to split the string into multiple uris. The default delimiter is comma, but can be re-configured.

Ignore Invalid Endpoints

The Routing Slip supports ignoreInvalidEndpoints (like Recipient List EIP). You can use it to skip endpoints which are invalid.

  • Java

  • XML

  • YAML

from("direct:start")
  .routingSlip(header("myHeader")).ignoreInvalidEndpoints();
<route>
  <from uri="direct:start"/>
  <routingSlip ignoreInvalidEndpoints="true">
    <header>myHeader</header>
  </routingSlip>
</route>
- route:
    from:
      uri: direct:start
      steps:
        - routingSlip:
            ignoreInvalidEndpoints: "true"
            expression:
              header:
                expression: myHeader

Then let us say the myHeader contains the following two endpoints direct:foo,xxx:bar. The first endpoint is valid and works. However, the second one is invalid and will just be ignored. Camel logs at DEBUG level about it, so you can see why the endpoint was invalid.

Back to top