Choice Flow Control Reference

Insert message processor 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 options. Note that 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.

Double-click to open the choice Flow Control’s Pattern Properties panel (below).

Mule displays a table with two columns: When and Route Message to. Notice, in the image above, that Mule displays a line item for each routing option. Mule identifies each routing option by its first message processor. Double-click the first empty line item in the Route Message to column to open the Route Properties panel (below).

In the Expression field, enter an expression for the choice router to use to evaluate the contents of a message. For example: #[payload['name'] == null]

Repeat the two preceding steps until you have supplied the choice flow control with a When expression for each non-default routing option (see example below).

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

Click OK to save the routing configurations.

As it processes messages, Mule evaluates the expressions defined in your routing options in order, top down, until one of them evaluates to "true". 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. In the code sample below, we have added an expression-transformer and a session-variable-transformer.

<flow name="New_Studio_ProjectFlow1" doc:name="New_Studio_ProjectFlow1">
        <http:inbound-endpoint exchange-pattern="request-response" host="localhost" port="8081" doc:name="HTTP"/>
        <choice doc:name="Choice">
            <when expression="">
                <expression-transformer doc:name="Expression"/>
                <session-variable-transformer doc:name="Session Variable"/>
            </when>
            <otherwise>
            </otherwise>
        </choice>
        <scripting:component doc:name="Groovy">
            <scripting:script engine="Groovy"/>
        </scripting:component>
</flow>

Configure the contents of one or more additional when elements to define multiple routing options for your choice element. Refer to code sample below.

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.

<flow name="New_Studio_ProjectFlow1" doc:name="New_Studio_ProjectFlow1">
        <http:inbound-endpoint exchange-pattern="request-response" host="localhost" port="8081" doc:name="HTTP"/>
        <choice doc:name="Choice">
            <when expression="">
                <expression-transformer doc:name="Expression"/>
                <session-variable-transformer doc:name="Session Variable"/>
            </when>
            <when expression="">
                <attachment-transformer doc:name="Attachment"/>
             </when>
            <otherwise>
                 <ftp:outbound-endpoint host="localhost" port="21" responseTimeout="10000" doc:name="FTP"/>
            </otherwise>
        </choice>
        <scripting:component doc:name="Groovy">
            <scripting:script engine="Groovy"/>
        </scripting:component>
    </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="#[payload['name'] == null]">

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.

Double-click to open the choice flow control icon, 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 pattern properties panel (below). (Note that the FTP routing option now needs a "when" expression defined.)

Mule applies the new routing order to the building blocks on the canvas. The new default routing option appears at the bottom of the scope.

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