Composite source is a scope available with mule ESB which listens to multiple channels for incoming messages. If any of the receivers or inbound endpoints receive the message, it passes to the next processor and results in triggering the flow. A scope in Mule is also known as a wrapper.

There can be a case where you need to define multiple sources to receive the messages. For example, you can receive purchase orders from various customers and every one has to send a message through different channels like File Share, Web Service or REST Call, JMS, SFTP, etc. But the way of handling or business process defined for each customer is same, so we can use the Composite source in such a case.

Let's walk through how to use Composite source with Mule Flow.

Search for Composite source in Mule Pallette and place it to the source region of flow.

 <flow name="composite-flowFlow">
        <composite-source doc:name="Composite Source"/>
    </flow>

Now you can drag and drop multiple connectors under composite source (i.e. wrap the multiple connectors with Composite source). In this case, we will use two HTTP Listeners and one File Connector as inbound endpoints to receive messages from different sources.

  <http:listener-config name="HTTP_Listener_Configuration" host="0.0.0.0" port="8081" doc:name="HTTP Listener Configuration"/>
    <http:listener-config name="HTTP_Listener_Configuration1" host="0.0.0.0" port="8082" doc:name="HTTP Listener Configuration"/>
    <flow name="composite-flowFlow">
        <composite-source doc:name="Composite Source">
            <http:listener config-ref="HTTP_Listener_Configuration" path="/cs" doc:name="HTTP" allowedMethods="POST"/>
            <http:listener config-ref="HTTP_Listener_Configuration1" path="/cs" doc:name="HTTP" allowedMethods="POST"/>
            <file:inbound-endpoint path="src/test/resources/in" responseTimeout="10000" doc:name="File"/>
        </composite-source>
    </flow>

Now, drag and drop the File connector in message processor region. Whenever an incoming message is received by any listener, it will pass to next processor. In this case, the message will be passed to File connector in message processor region.

<?xml version="1.0" encoding="UTF-8"?>

<mule xmlns:file="http://www.mulesoft.org/schema/mule/file" xmlns:http="http://www.mulesoft.org/schema/mule/http" xmlns="http://www.mulesoft.org/schema/mule/core" xmlns:doc="http://www.mulesoft.org/schema/mule/documentation"
xmlns:spring="http://www.springframework.org/schema/beans" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-current.xsd
http://www.mulesoft.org/schema/mule/core http://www.mulesoft.org/schema/mule/core/current/mule.xsd
http://www.mulesoft.org/schema/mule/http http://www.mulesoft.org/schema/mule/http/current/mule-http.xsd
http://www.mulesoft.org/schema/mule/file http://www.mulesoft.org/schema/mule/file/current/mule-file.xsd">
    <http:listener-config name="HTTP_Listener_Configuration" host="0.0.0.0" port="8081" doc:name="HTTP Listener Configuration"/>
    <http:listener-config name="HTTP_Listener_Configuration1" host="0.0.0.0" port="8082" doc:name="HTTP Listener Configuration"/>
    <flow name="composite-flowFlow">
        <composite-source doc:name="Composite Source">
            <http:listener config-ref="HTTP_Listener_Configuration" path="/cs" doc:name="HTTP" allowedMethods="POST"/>
            <http:listener config-ref="HTTP_Listener_Configuration1" path="/cs" doc:name="HTTP" allowedMethods="POST"/>
            <file:inbound-endpoint path="src/test/resources/in" responseTimeout="10000" doc:name="File"/>
        </composite-source>
        <file:outbound-endpoint path="src/test/resources/out" responseTimeout="10000" doc:name="File"/>
    </flow>
</mule>

Testing The Application

You can use Postman to test the application. In this case, there are two HTTP Listeners and one File endpoint listening to incoming messages.

Similarly, you can use other receivers to trigger the flow.

Now, you know how to use the Composite source in Mule Flow.