Module 9: Controlling Event Flow

Table of Contents

About

1.

Objectives

  • Multicast events
  • Route events based on conditions
  • Validate events

Notes

Intro

Module 4: Controlling event flow

Two ways of retrieving data by providing the ability to retrieve

  • The combined results of all airlines
  • A single airline or combined

At the end of this module, you should be able to

  • Multicast events
  • Route events based on conditions
  • Validate events

Routing events

Topic video

  • Routers

    • Routers send events to one or more groups of event processors (routes)
    • Choice: one route executed based on conditional logic
    • First Successful: routes executed sequentially until one is successfully executed
    • Round Robin: one route executed, which one is selected by iterating through a list maintained across executions
    • Scatter-Gather: all routes executed concurrently

Extras

  • Topic slides

  • Event Flow Control Explained | Lightboard session

    • Choice

      • Provides multiple paths


        Choice Router

      • Functions like a switch statement in Java and other languages

      • How it works

        • A condition is specified on each path, and then a default path is set
        • It runs from top to bottom looking or a successful condition to execute
        • Any successful condition in one of the before the default path is executed, otherwise the default is executed

    • Scatter-Gather

      • Provides multi-threaded functionality
      • Very useful when there is need to cut down the response time

      • How it works

        • One thread in, Multithreaded, one thread out the other side


          Scatter-Gather

        • Use if A, B and C can be executed in parallel without having to wait for the result of one in order to call the next step

        • Scatter

          • It spins up multiple threads
          • All parts are executed, each with their own thread

        • Gather part

          • Then the ‘gather part’ combines the results that came out of each of the paths into a unified single event coming out

    • Round Robin

      • Useful when communicating with a system that doesn’t have a load balancer to distribute load
      • E.g. if you need it to distribute different order between two different JMS queues, or to talk to two different servers without load balancers
      • It does the load balancing or the load distributing by different paths
      • Not necessary if there is a load balancer between Mule (client) and the system you’re communicating with (consumer)

      • How it works


        Round Robin

        • When the first request comes in, it goes down path A
        • When another request comes in, new event, goes down path B…
        • And then it loops back to the top

    • First Successful

      • It has to do with the errors returned i.e. if errors are returned by any of the paths, it will keep moving down the list
      • It doesn’t need a condition, neither is it doing multi-threaded execution

      • How it works

        • It will first try the top most one, if that fails
        • It tries the second…

Multicasting events

Topic video

  • The Scatter-Gather router

    • Scatter-Gather sends the event to each route concurrently and returns a collection of all results

    • Collection is an object of objects

      • Each object contains attributes and payload from each Mule event returned from a flow

  • Walkthrough 4-1: Multicast an event

    • Use a Scatter-Gather router to concurrently call all three flight services
    • Use DataWeave to flatten multiple collections into one collection

Routing events based on conditions

Topic video

  • The Choice router


    Choice Router

    • Sends the event to one route based on conditional logic
    • The conditions are written with DataWeave

  • Walkthrough 4-2: Route events based on conditions

    • Use a Choice router
    • Use DataWeave expressions to set the router paths
    • Route all flight requests through the router

Validating events

Topic video

  • Validators

    • Provide a way to test some conditions are met and throw an error if the validation failes

    • To use

      • Add the Validation module to a project
      • Select a validation operation

  • Walkthrough 4-3: Validate events


    Validate Events

    • Add the Validation module to a project
    • Use an Is true validator to check if a query parameter called code with a value of SFO, LAX, CLE, PDX or PDF is sent with a request
    • Return a custom error message if the condition is not met

Summary

Use different routers and validators to control event flow

Use the Choice router to send an event to one route based on conditional logic

Use the Scatter-Gather router to send an event concurrently to multiple routes

  • A collection of all results is returned
  • Use DataWeave to flatten the collection

Use the Validation module to specify whether an even can proceed in a flow

Test your knowledge

What module and operation will throw an error if a Mule event’s payload is not a number?

  • Validation module’s Is number operation

An event contains a payload that is an Array of Objects. How is the event routed in a Scatter-Gather?

  • The ENTIRE event is sent to each route and passed in PARALLEL

Refer to the exhibits. What happens to this flow when the Validation module’s Is not null operation throws an error?

[[/img/Validation-question.png]

  • The flow stops processing its Mule event and returns an error message to the HTTP Listener operation

A Scatter-Gather processes three separate HTTP requests. Each request returns a Mule event with a JSON payload. What is the final output of the Scatter-Gather?

  • An Object containing all three Mule event Objects

How are multiple conditions used in a Choice router to route events?

  • To find the FIRST true condition, then distribute the event to the ONE matched route

Anki

References

  1. . “Module 9: Controlling event flow”. Available at: . (Accessed: [2025-03-09 Sun 20:47]). ↩︎

Random Posts