Choice Flow Control Reference

Insert message processors within the dashed line area that signifies the choice flow control scope to define the routing options, making sure to place one of them within the "Default" box to define it as the default routing option. You can place several message processors in a chain for each routing option, as needed. In our example, shown below, we have defined three routing options to reply in Spanish, French, or English:

Click the Choice Router building block to open its Properties Editor. Here, enter Mule expressions to define the routing logic that Mule applies to incoming messages (see table below; detailed instructions follow).

In the table, double-click the first empty row under When:

In the Route Properties dialog, enter: #[flowVars.language == 'Spanish']

Click OK. This expression tells Mule to look for a flow variable called language on the incoming message and check whether it equals Spanish. If this expression evaluates to true, Mule routes the message to the message processor in that path.

Click the next empty row, and enter: #[flowVars.language == 'French']

Click OK to save the routing configurations.

Double-click the Default line item to open its Route Properties panel.

Next, click the topmost Set Payload building block within your Choice Router scope to open its Properties Editor and set Value to: `Hola! `

Click the next Set Payload building block for Reply in French and set the value to:

Bonjour!

Click the Variable Transformer inside the Default box to open its Properties Editor, then configure it as:

Click the Set Payload after the Variable Transformer inside the Default box to open its Properties Editor, then configure it as:

If necessary, drag and drop building blocks within the choice flow control scope on the canvas to reorder routing options.

To the first when element within your choice element, add message processors as child elements to form a routing option to which the choice element can direct messages. Add as many additional when elements as needed.

<http:listener-config name="HTTP_Listener_Configuration" host="localhost" port="8081" doc:name="HTTP Listener Configuration"/>
<flow name="New_Studio_ProjectFlow1" doc:name="New_Studio_ProjectFlow1">
        <http:listener config-ref="HTTP_Listener_Configuration" path="/" doc:name="HTTP"/>
        <expression-filter expression="#[message.inboundProperties.'http.request.uri' != '/favicon.ico']" doc:name="Expression"/>
        <set-variable variableName="language" value="#[message.inboundProperties.'http.query.params'.language]" doc:name="Set Language Variable"/>
        <choice doc:name="Choice">
            <when expression="">
                <set-payload value="Hola!" doc:name="Reply in Spanish"/>
            </when>
            <when expression="">
                <set-payload value="Bonjour!" doc:name="Reply in French"/>
            </when>
            <otherwise>
            </otherwise>
        </choice>
        <logger message="#[payload]" level="INFO" doc:name="Logger"/>
</flow>

Configure the contents of the otherwise child element to define the default routing option to which your choice router can direct messages if all the previous when expressions evaluate to false. Refer to code sample below.

<http:listener-config name="HTTP_Listener_Configuration" host="localhost" port="8081" doc:name="HTTP Listener Configuration"/>
<flow name="New_Studio_ProjectFlow1" doc:name="New_Studio_ProjectFlow1">
        <http:listener config-ref="HTTP_Listener_Configuration" path="/" doc:name="HTTP"/>
        <expression-filter expression="#[message.inboundProperties.'http.request.uri' != '/favicon.ico']" doc:name="Expression"/>
        <set-variable variableName="language" value="#[message.inboundProperties.'http.query.params'.language]" doc:name="Set Language Variable"/>
        <choice doc:name="Choice">
            <when expression="">
                <set-payload value="Hola!" doc:name="Reply in Spanish"/>
            </when>
            <when expression="">
                <set-payload value="Bonjour!" doc:name="Reply in French"/>
            </when>
            <otherwise>
                <set-variable variableName="language" value="English" doc:name="Set Language to English"/>
                <set-payload value="Hello!" doc:name="Reply in English"/>
            </otherwise>
        </choice>
        <logger message="#[payload]" level="INFO" doc:name="Logger"/>
</flow>

For each when element, enter an expression for the choice router to use to evaluate the contents of a message. If, during processing, the expression associated with a routing option evaluates to true, Mule directs the message to that route. Refer to example expression below.

<when expression="#[flowVars.language == 'Spanish']">

As it processes messages, Mule evaluates the expressions defined in your routing options in the order they appear in the config, top down, until one of them evaluates to "true". Adjust the order of the when elements in your flow with this in mind.

Open the Choice Flow Control’s Properties Editor, then, in the table, double-click the line item of whichever routing option that you would like to specify as the new default route.

Check the Otherwise box (see below), then click OK.

Mule applies the Default label to the new default routing option in the table on the Properties Editor (below). (Note that the English routing option now needs a "when" expression defined.)

Define a when expression for the routing option previously identified as the default. (In the example, the English routing option.)