The document summarizes a MuleSoft meetup in Patna, India about exception handling in Mule 4. The agenda includes introductions, an overview of exception handling, how to implement exception handling in Mule 4 using various techniques like error handlers, on error continue/propagate, try scope, and raising errors. It also discusses system exception handling, differences between Mule 3 and 4, and error handling generated by APIkit routers. The meetup includes interactive examples and a quiz with prizes for participants.

1. Patna, India
[09th May 2020]
[ Exception handling in Mule 4 & Develop a Simple API,
Deploy it to Hub]

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Welcome to Patna MuleSoft Meetup Group
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Introductions
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• About the organizer:
– Patna MuleSoft Meetup Group
• About the speakers:
Welcome everyone! Thanks for joining us!

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participants and let’s show on social channels #MuleSoftMeetup
We are connected. Thank you!

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Agenda
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 Introductions
 What is Exception handling
 How to do Exception Handling in Mule 4
 Error Handler
 On Error Continue , On Error Propagate
Try scope
 Raise Error
 Error handling generate by API-Kit Router
 Develop a Simple API, Deploy it to Hub Networking time

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Surprises!
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• Participate in an online
Quiz to win the
instructor-led training
classes and certification
exam vouchers. (3
Winners!)
• Be geared up for the
quiz sessions at the end


8. [Exception Handling]

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What is Exception Handling
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• An exception occurs when an unexpected event happens while
processing.
• Exception handling is the process of responding to exceptions when a
computer program runs.
• Exception handling attempts to gracefully handle these situations so
that a program (or worse, an entire system) does not crash.
• Exception handling can be performed at both the software (as part of
the program itself) and hardware levels (using mechanisms built into
the design of the CPU).

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Different type of Errors/Exceptions
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• In General Errors/Exceptions are categorized in 2 groups
– Message Exception
• Thrown with in a flow when mule event is involved
– System Exception
• Thrown with in a flow when no mule event is involved
• Error that occur
– During Mule Start up
– When connection to External system fails

11. [Exception Handling in Mule 4]

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Message Exception Handling in Mule 4
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• Like any programming language Mule also provide ways to handle
exception.
• In Mule we can handle the message exception at different level.
– At Project level using Default error handler
– At Project level using Custom Global error handler
– At Flow level in exception handling using On Error Continue and On Error
Propagate, Raise Error
– With in Flow or at processor level using try scope

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Message Exception Handling in Mule 4
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• When an event is being processed through a Mule flow that throws
an error
– Normal flow execution stops
– The event is passed to the first processor in the error handler

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Information about error
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• When a error is thrown, an error object is created
• Two of error object properties are
– error.description – a string
– error.errorType – an object
• Error type is identified by namespace and indentifier
– HTTP:UNATHORIZED

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Error Type hierarchy
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• Like in Java class/object follow hierarchy in mule error types also
follow hierarchy
• Each Error type has a parent
• The error type ANY is the most general parent like Object class is
the parent class of all the classes in java by default.

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Error Type hierarchy reference
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17. [Error Handler]

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Error Handler in Java
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Try {
//Processing
//...
//...
} Catch (err) {
//Catch exception and do processing
//...
//...
}

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Default Global Error Handler
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• If there is no error handling written at any of the levels, the Mule
Default Error Handler is used, which stops the execution of the
flow and logs the exception.
• The Mule Default Error Handler is not configurable but, can be
replaced by our Custom Global error handler by creating a
Configuration global element.

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Custom Global Error Handler
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• To handle errors at the application level, we can add an error handler
in the global.xml (or simply outside a flow).
• Then, create a Configuration element in the global elements, which
sets the Global Error Handler as the Default Error Handler.

21. [On Error Propagate]

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On Error Propagate
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• All processors within error handling scope are executed
• At the end of the flow
– Rest of the flow that threw error does not executed
– The error is rethrown up to the next level and handled there
• An HTTP listener return error response with default status code 500

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Visualize On Error Propagate like Java
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Try {
//Processing
//...
//...
} Catch (err) {
//Catch exception and do processing
//...
//Re-Thorough error
}

24. [On Error Continue]

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On Error Continue
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• All processor within error handling scope executed
• At the end of the flow
– Rest of the flow that threw error does not executed
– The event is passed up to the next level as if flow execution had completed
successfully
• An HTTP listener return success response with default status code
200

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Visualize On Error Continue like Java
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Try {
//Processing
//...
//...
} Catch (err) {
//Catch exception and do processing
//...
//Success and continue normal path
}

27. Lets get our hands dirty 

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Error handling scenario 0
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Error handling scenario 0 - Execution
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Error handling scenario 1
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Error handling scenario 1 - Execution
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Error handling scenario 2
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Error handling scenario 2 - Execution
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Error handling scenario 3
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Error handling scenario 3 - Execution
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Error handling scenario 4
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Error handling scenario 4 - Execution
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38. How Can we Make a For loop
keep Running even if a record
fails during looping ?

39. [Try scope]

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Handling errors with flow – Try Scope
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• Using try scope we can handle error within a
flow
• Try scope give us more control to handle
error at processor level
• One and more processors can be added in
try scope
• Try scope have its own error handling
section

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Handling errors with flow - Execution
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Custom error types
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• When you have same processor which can throw exception in a flow
at multiple places we can use custom error types to
distinguish/differentiate which component/processor have raised the
exception
• You assign custom namespace and identifier to differentiate them
from other existing types
• Do not use existing module namespaces

43. [Raise Error]

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Raising custom errors
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• Apart from mapping existing error to custom
error mule also provide to raise custom
exceptions
• Raise error give us freedom to raise custom
exception

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Raising custom errors - Execution
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46. [Error handling generate by
API-Kit Router]

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Error handling generate by API-Kit Router
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• By default, interfaces created with APIkit have error handlers with
multiple On Error Propagate scopes that handle API-kit errors
– The error scopes set HTTP status codes and response messages
• The main routing flow has six error scopes
– APIKIT: BAD_REQUEST > 400
– APIKIT:NOT_FOUND > 404
– APIKIT:METHOD_NOT_ALLOWED > 405
– APIKIT:NOT_ACCEPTABLE > 406
– APIKIT:UNSUPPORTED_MEDIA_TPYE > 415
– APIKIT: NOT_IMPLEMENTED > 501

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Error handling generate by API-Kit Router
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• In most cases the default
generated error scopes are
sufficient
• You can modify default
generated error scopes and
even can add new error scopes
as per your requirement

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System Exception Handling in Mule 4
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• System exceptions can be handled in mule using retry/reconnection
and Until Successful

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Difference between Error Handling in Mule 3 & 4
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Mule 4 Mule 3
On Error Continue, On Error Propagate, Try
Scope are new options available
Catch, Choice and Reference exception
strategy are the few option available
Error handling can be done at processor level
using try scope
It was not possible in Mule 3
Error Handling at sub-flow is possible using
try scope
It was not possible in Mule 3
Transaction are possible using try scope Rollback strategy need to use to undo
transaction in case of errors
Custom Errors can be raised using Raise
Error
It was not possible in Mule 3
Custom Error mapping of existing exception
is possible
It was not possible in Mule 3
Easier and more granular error handling is
possible
It was little bit difficult to implement error
handling

51. Q & A

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Take a stand !
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• Nominate yourself for the
next meetup speaker and
suggest a topic as well.
• Share your interest:
bit.ly/SpeakersPatnaMotihari
• Either for our virtual meetup
speaker, or in-person
meetup speaker in Bihar.
• Surprise swag for upcoming
Speakers.

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What’s next
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• Share:
– Tweet/share in LinkedIn , facebook, Instagram with your pictures with the hashtag
#PatnaMuleMeetup #MuleSoftMeetup
– Also use #BringMuleSoftConnectToPatna to reach our wish to MuleSoft 
– Invite your network to join: https://meetups.mulesoft.com/Patna/
• Feedback:
– Please fill out the slips with details like are you new to Mule? If so what technology you are
currently working , What makes you to think of adopting MuleSoft and what topic you are
expecting in future Meetups
– Contact MuleSoft at meetup@mulesoft.com for ways to improve the program
– Instagram Page for Patna to be created
– Your Feedback is Food for us
• Our next meetup:
– Date: TBD
– Location: Patna/Virtual
– Topic: TBD

54. THANK YOU 
#Everyone
for becoming a part of such a great
#community.

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MuleSoft CONNECT Digital is a live virtual experience — bringing
you a full program of educational sessions and content, streamed
online for free.
AMER: May 20, 2020
EMEA: June 4, 2020
JAPAC: June 25, 2020
Register for free: https://connect.mulesoft.com

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Meet the MuleSoft Community at:
- Our digital community booth
- Q&A sessions with MuleSoft Ambassadors
- Our special Developer Meetup
JOIN ONLINE FOR FREE:
AMER: May 20, 2020
EMEA: June 4, 2020
JAPAC: June 25, 2020
Register: https://connect.mulesoft.com

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Developer Meetup @ CONNECT AMER
● UCSF
○ Veera Gopalakrishnan, System Integration Engineer
○ Dynamic DataWeave for secure access to UCSF EHR
data
● MuleSoft Ambassador
○ Joshua Erney
○ The best thing to happen to DataWeave since sliced
bread: the Update Function.
JOIN FOR FREE: May 20, 2020 (12:30-2:30pm PST)
Register: https://connect.mulesoft.com

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MuleSoft Training
COVID-19 Response
April 2020

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MuleSoft Training is open for business!
● All MuleSoft courses and certification exams can be taken
virtually in every region
● In response to COVID-19, all current certifications that expire
between February 1 - July 31, 2020 will remain valid through
July 31, 2020
● Certification exam online proctoring requirements:
○ Webcam (you can use the one in your computer!)
○ Reliable internet connection
○ For more details, go to our Certification Help Center
Check out our blog post for more info on training and certification!

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How long does it run?
From the week of April 13 - until the end of May.
Who can attend?
Any learner who enrolls or is currently enrolled in:
Development Fundamentals (Mule 4)
How can I attend?
Sign up for your desired sessions at:
https://training.mulesoft.com/covid19-lecture-series
Global schedule of webinars:
JAPAC - 15:00-17:00 AEST
EMEA - 10:00-12:00 BST / 11:00-13:00 CET
AMER - 9:00-11:00 PST / 12:00-14:00 EST
Free Instructor Lecture Series for MuleSoft.U
60
Mondays
● Module 1: Introducing Application Networks and API-Led
Connectivity
● Module 2: Introducing Anypoint Platform
● Module 3: Designing APIs
Tuesdays
● Module 4: Building APIs
● Module 5: Deploying and Managing APIs
● Module 6: Accessing and Modifying Mule Events
Wednesdays
● Module 7: Structuring Mule Applications
● Module 8: Consuming Web Services
● Module 9: Controlling Event Flow
Thursdays
● Module 10: Handling Errors
● Module 11: Writing DataWeave Transformations
Fridays
● Module 12: Triggering Flows
● Module 13: Processing Records
Note that these are not full instructor-led courses, but rather review sessions to cover the material you
will learn in our self-paced course.

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Quiz
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○Win 1 of 3 free instructor-led training courses & Certification voucher

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What’s next
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• Share:
– Tweet your pictures with the hashtag #MuleSoftMeetup
– Invite your network to join: meetups.mulesoft.com/patna
• Feedback:
– Suggest the topics and nominate your self as our next Meetup
Speakerbit.ly/SpeakersPatnaMotihari
– Contact MuleSoft at meetup@mulesoft.com for ways to improve the program
• Our next meetup:
– Date: TBD
– Location: Patna/Virtual
– Topic: TBD

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Networking Time
Share Anything

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See you next time!
Please send topic suggestions to the organizer:
bit.ly/SpeakersPatnaMotihari
Thank you everyone for joining us today