Over a million developers have joined DZone.

Parallel Processing in Mule

DZone's Guide to

Parallel Processing in Mule

In parallel processing, a list of actions is executed concurrently but independently. Learn to achieve this with Scatter-Gather in Mule in this tutorial.

· Integration Zone ·
Free Resource

WSO2 is the only open source vendor to be named a leader in The Forrester Wave™: API Management Solutions, Q4 2018 Report. Download the report now or try out our product for free.

Parallel processing is a technique where a list of actions can be executed concurrently but independently and the parent flow will not continue until all actions are completed. This can be done in Mule using Scatter and Gather flow control. 

Consider an example: a flow should call 2 REST services concurrently and combine the result and return.


We are going to use the below REST API in our flow, which returns a post per call and takes Post Id in the URI. Below is a screenshot from POSTMAN tool.

Image title

Code Sample

Start your flow with an HTTP Listener and configure it with 8081 port; following that, drag a Scatter-Gather Flow control. In each flow, get an HTTP connector like below to call a REST Service.

Image title

After the Scatter-Gather flow control, get a DataWeave Transform connector which does the actual transformation. Our transform shape would look like below. We could access the output of Scatter-Gather like an arraylist in the transformation.

Image title

Our flow would look like this:

Image title

Our successful run of this flow from POSTMAN would look like this:

Image title

Code View

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

<mule xmlns:dw="http://www.mulesoft.org/schema/mule/ee/dw" xmlns:json="http://www.mulesoft.org/schema/mule/json" xmlns:scripting="http://www.mulesoft.org/schema/mule/scripting" 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"
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/json http://www.mulesoft.org/schema/mule/json/current/mule-json.xsd
http://www.mulesoft.org/schema/mule/scripting http://www.mulesoft.org/schema/mule/scripting/current/mule-scripting.xsd
http://www.mulesoft.org/schema/mule/ee/dw http://www.mulesoft.org/schema/mule/ee/dw/current/dw.xsd">
    <http:listener-config name="HTTP_Listener_Configuration" host="" port="8081" doc:name="HTTP Listener Configuration"/>
    <http:request-config name="HTTP_Request_Configuration" host="jsonplaceholder.typicode.com" port="80" doc:name="HTTP Request Configuration"/>
    <flow name="scattergathersampleFlow">
        <http:listener config-ref="HTTP_Listener_Configuration" path="/samples" allowedMethods=" GET" doc:name="HTTP"/>
        <scatter-gather doc:name="Scatter-Gather">
            <http:request config-ref="HTTP_Request_Configuration" path="/posts/1" method="GET" doc:name="Get Post1"/>
            <http:request config-ref="HTTP_Request_Configuration" path="/posts/2" method="GET" doc:name="Get Post2"/>
        <dw:transform-message doc:name="Transform Message">
            <dw:set-payload><![CDATA[%dw 1.0
%output application/json
flatten payload]]></dw:set-payload>

Scatter Gather is a costly operation because it uses multiple threads to complete the list of actions, but it executes the actions concurrently and independently. It will not complete until all the actions are completed in all the branches. 

Using the transform shape, we could create a single output from different types of message and we could access them like an ArrayList:

%dw 1.0
%output application/json
post1: payload[0].body,
post2: payload[1].body


Or we could just combine all the ResultSets using the below code snippet:

%dw 1.0
%output application/json
flatten payload

Handling exceptions inside scatter gather

if you have a direct call or a subflow inside the scatter gather your parent flow's exception handling will take effect. If you need to take care of the exceptions individually have a flow in the place of subflow like below.

Image title

In the "combine-all-3-responses" transform component now either I will receives each component's failure or successful payload. My each flow will be similar to this.

Image title

IAM is now more than a security project. It’s an enabler for an integration agile enterprise. If you’re currently evaluating an identity solution or exploring IAM, join this webinar.

mule esb ,mule flow ,integration ,tutorial ,mule ,scatter-gather

Opinions expressed by DZone contributors are their own.

{{ parent.title || parent.header.title}}

{{ parent.tldr }}

{{ parent.urlSource.name }}