Recipient List

Overview

A recipient list, shown in Figure 5.3, is a type of router that sends each incoming message to multiple different destinations. In addition, a recipient list typically requires that the list of recipients be calculated at run time.

Figure 5.3. Recipient List Pattern

Recipient list with fixed destinations

The simplest kind of recipient list is where the list of destinations is fixed and known in advance, and the exchange pattern is InOnly. In this case, you can hardwire the list of destinations into the to() Java DSL command.

	Note
	The examples given here, for the recipient list with fixed destinations, work only with the InOnly exchange pattern (similar to a pipeline). If you want to create a recipient list for exchange patterns with Out messages, use the multicast pattern instead.

Java DSL example

The following example shows how to route an InOnly exchange from a consumer endpoint, queue:a, to a fixed list of destinations:

from("seda:a").to("seda:b", "seda:c", "seda:d");

XML configuration example

The following example shows how to configure the same route in XML:

<camelContext id="buildStaticRecipientList" xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="seda:a"/>
    <to uri="seda:b"/>
    <to uri="seda:c"/>
    <to uri="seda:d"/>
  </route>
</camelContext>

Recipient list calculated at run time

In most cases, when you use the recipient list pattern, the list of recipients should be calculated at runtime. To do this use the recipientList() processor, which takes a list of destinations as its sole argument. Because FUSE Mediation Router applies a type converter to the list argument, it should be possible to use most standard Java list types (for example, a collection, a list, or an array). For more details about type converters, see Built-In Type Converters in Programmer's Guide.

Java DSL example

The following example shows how to extract the list of destinations from a message header called recipientListHeader, where the header value is a comma-separated list of endpoint URIs:

from("direct:a").recipientList(header("recipientListHeader").tokenize(","));

In some cases, if the header value is a list type, you might be able to use it directly as the argument to recipientList(). For example:

from("seda:a").recipientList(header("recipientListHeader"));

However, this example is entirely dependent on how the underlying component parses this particular header. If the component parses the header as a simple string, this example will not work. You must know how the underlying component parses its header data (see ????).

XML configuration example

The following example shows how to configure the preceding route in XML, where it is assumed that the underlying component parses the foo header as a list type:

<camelContext id="buildDynamicRecipientList" xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="seda:a"/>
    <recipientList>
      <header>recipientListHeader</header>
    </recipientList>
  </route>
</camelContext>