Mule ESB Interview Questions And Answers

Are you planning to attend an interview for the Mulesoft role but confused on how to crack that interview and also what would be the most probable Mule ESB Interview Questions that the interviewer may ask? Well, you have reached the right place. Tekslate has collected the most frequently asked Mulesoft Interview Questions and Answers which are often asked in multiple interviews.

Categories Of Mule ESB Interview Questions

Q1) What is Mule?

Ans: Mule ESB (a.k.a. Mule) is a lightweight Java-based enterprise service bus (ESB) and integration platform that allows developers to connect applications quickly and easily, enabling them to exchange data. Mule ESB enables easy integration of existing systems, regardless of the different technologies that the applications use, including JMS, Web Services, JDBC, HTTP, and more.

Q2) What is ESB?

Ans: An enterprise service bus (ESB) is a software architecture for middleware that provides fundamental services for more complex architectures. For example, an ESB incorporates the features required to implement a service-oriented architecture (SOA). In a general sense, an ESB can be thought of as a mechanism that manages access to applications and services (especially legacy versions) to present a single, simple, and consistent interface to end-users via Web- or forms-based client-side front end.

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Q3) What are all the Primitives used in Mediation?

Ans: We have different types of primitives in mediation.

  • Message Filter
  • Type Filter
  • Endpoint Lookup
  • Service Invoke
  • Fan-out
  • Fan-in
  • XSLT
  • BO Map
  • Message Element Setter
  • DB lookup
  • Data Handler
  • Custom Mediation
  • Header Setters
  • Message Logger
  • Even Emitter
  • Stop
  • Fail
  • Sub Flow

Q4) What is  Shared Context?

Ans: Shared Context: Context is a temporary area that is created along with Service Message Object (SMO) in the Mediation Flows. Shared Context is a type of context which is present in the SMO. Shared Context is mainly used when we are using the Aggregation process where we need to Iterate the BO for Certain times. Shared Context maintains Aggregation data between Aggregation (FanOut and FanIn) primitives. The Content (data) which is present in the shared context BO does not persist across Request and Response flows i.e. The Data in the Shared Context which is used in Request flow can not be used again in Response flow.

Q5) What is Transient Context?

Ans: Transient Context: Used for passing values between Mediation primitives within the current flow — either the request flow or the responses flow. The transient context cannot link requests and responses and hence cannot be used across.

Used when you want to save an input message before a service invokes a call (within a request or response flow). After the services invoke call, the next primitive can create another message by combining the service invoke response and the original message stored in the transient context.

MuleSoft Interview Questions And Answers

Q6) What is the Correlation Context?

Ans: Correlation Context: Used when Mediation primitives want to pass values from the request flow to the response flow.

Used to pass values from the request message onto the response.

Q7) Difference between Callout and Service Invoke?

Ans: Service Invoke: The Service Invoke primitive is used to make a service request in either a request or response mediation flow. The service may be Request/Response or One-Way. Multiple instances of the Service Invoke primitive are permitted in a flow, allowing a series of service invocations to be performed.

Callout: The Callout receives the message and calls the requested service and operation. There is a Callout node for each connected target operation in the mediation flow.

  • If the call is successful, the Callout Response node in the response flow receives the response message.
  • If the call is unsuccessful, the Callout can be set to retry service invocations depending on the type of fault received.

Q8) How can you implement a loop in mediation?

Ans: By using Fan-in and Fan-out primitive.

Q9) What is the functionality of Fan-in and Fan-out?

Ans: Fan-out: We can use the Fan Out primitive to fire the output terminal once (with the input message) or fire the output terminal multiple times. You can use Fan Out in isolation or as part of a Fan-Out and Fan In combination.

Fan-In: Fan In is always partnered with a Fan-Out in the same flow and acts as a decision point for when to continue flow execution. It receives a number of messages until a decision point is reached, at which point the last message to be received is propagated to the output terminal. The Fan In primitive may only be used in combination with Fan-Out.

Q10) How can you change the runtime changes using mediation primitive?

Ans: We have a future called Promotable properties in ESB training Bangalore. We can configure this future while developing. Then we can make it changed at runtime without restarting the server it can be published.

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Q11) What are all the configurations required for JDBC Adapter implementation?

Ans: Data Source needs to be created and needs to configure with DB. If we have security, then need to created security authentication.

Q12) What is the Difference between SDO and SMO?

Ans: SDO: Service Data Object is the representation of the variable or Object.

SMO: The SMO model is a pattern for using SDO Data Objects to represent messages

Q13) What is the difference between Stop and fail?

Ans: Stop: Stops a particular path in the flow, without generating an exception.

Fail: Generates a failure in the flow.

Q14) Why am I getting 'Unable to get resource from repository' while building the Mule examples?

Ans: If you are getting this error message while building the Mule examples:

[WARNING] Unable to get resource from repository atlassian-m2-repository (


[WARNING] Unable to get resource from repository atlassian-m1-repository (


[WARNING] Unable to get resource from repository Codehaus (


[WARNING] Unable to get resource from repository codehaus-snapshots (

[INFO] ------------------------------------------------------------------------


[INFO] ------------------------------------------------------------------------

[INFO] Failed to resolve artifact.

You may need to change the version value of the dependency in the pom.xml, for instance,





The issue regarding dependencies review is tracked at MULE-1446.

Q15) How to use Mule HQ with Mule?

Ans: Mule Configuration

Add the following code snippet to your Mule configuration:


   <!-- starts an RMI registry on the default port 1099. -->















  • Start your Mule instance.
  • Ensure the HQ agent is running on the server the Mule instance is configured on and is pointing to the desired HQ server.
  • Check the Mule HQ server page to see if information about the Mule instance is being received.

Mule ESB Interview Questions For Freshers

Q16) What is a Mule UMO?

Ans: A Mule UMO is a Universal Message Object

UMO is now a legacy term. What was once referred to as UMO Components are now referred to as Service Components

Q17) A mule won't start? Check your Environment?

Ans: The java and mule environment variables must be set up correctly for a mule to start. If you are experiencing problems check the following variables:

  • MULE_HOME - should be the location of the mule install
  • JAVA_HOME - should be the location of the JDK
  • PATH - should have both JAVA_HOMEbin and MULE_HOMEbin in the path.
  • Check all of the above carefully.  Some systems with multiple JDK's installed can end up with incorrect mappings between the PATH and the JAVA_HOME, which will stop the mule from loading.

Q18) How to add classes/jars to the Mule classpath?


  • Use the MULE_LIB variable (generally set in the run script)
  • To include JAR file(s) in a mule classpath, declare each dependent jar file in the MULE_LIB entry.
  • For spring resource, if the XML bean declaration is placed within a project, including the project JAR file in the classpath too (i.e., if not included, Mule will throw a **.xml not found on the classpath)

Q19) How to configure a simple FTP handler in Mule?

Ans: ftp_handler-config.xml

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

<!DOCTYPE mule-configuration PUBLIC "-//MuleSource //DTD mule-configuration XML V1.0//EN"


<mule-configuration id="ftp_handler"version="1.0">


   Ftp get to a remote server and place into a local directory on the MULE server



  An interceptor is a piece of code that can be configued to execute

   before and/or after an event is received fora component.

   You can define a stack of interceptors that will be executed in sequence.

   You can then configure the stack on your components.


 <interceptor-stack name="default">

     <interceptor className="org.mule.interceptors.LoggingInterceptor"/>

     <interceptor className="org.mule.interceptors.TimerInterceptor"/>



    The Mule model initialises and manages your UMO components


 <model name="Retrieve_File">


         A Mule descriptor defines all the necessary information about how your components will
interact with the framework, other components in the system and external sources. 
Please refer to the Configuration Guide fora full description of all the parameters.


  <mule-descriptor name="ftpInbound"



          <endpoint address="ftp://mule:mule@localhost/ftp">

     <filter pattern="*.txt"



         <property name="binary"value="false"/>

         <property name="pollingFrequency"value="1000"/>

         <property name="filename"value="document.txt"/>

         <property name="outputPattern"value="FtpFile-${DATE}.done"/>





      <router className="org.mule.routing.outbound.OutboundPassThroughRouter">

          <endpoint address="file:///C:/MULE/inbound"/>




      Here we tell thiscomponent to use the interceptor stack defined above


   <interceptor name="default"/>




Q20) What is Mule Data Integrator?

Ans: Mule has released a data integrator tool, it is a visual mapping tool that supports flat-file, java object, XML mappings, etc. Coding complex mappings can be very tedious and additionally difficult to maintain, the mule data integrator with drag and drop facilities makes building and maintaining mappings very simple.

The mapping is done in eclipse (plugins required) and executed on a data integrator runtime that sits on top of Mule ESB - this requires a license.

Q21) Where to find the class Abstract Mule TestCase?

Ans: This is in 1.4/1.4.1 distributions but was missing from the 1.3.3 distribution - the class is defined in <mulehome>/lib/mule/mule-core-<version>.jar.

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Q22) What is a Web service API?

Ans: Application Programming Interface (API) is the means to write code by third parties to interface with another system. A Web Service is one of the types of API that always operates over HTTP like SOAP and other transports like SMTP. What is Flow Processing Strategies? The strategies of Flow Processing are majorly seven in number as follows:

  • Synchronous Flow Processing Strategy
  • Custom Processing Strategy
  • Queued Flow Processing Strategy
  • Thread Per Processing Strategy