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Top Mule ESB (MuleSoft) frequently asked interview questions | JavaInUse

Top Mule ESB (MuleSoft) frequently asked interview questions.

In this post we will look at Mule ESB (MuleSoft) Interview questions. Examples are provided with explanations.

Q: What is Mule ?
Mule ESB (a.k.a. Mule) is a lightweight Java-based enterprise service bus (ESB) and integration platform that allows developers to connect applications together 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.

Q: What is ESB ?
An enterprise service bus (ESB) is 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 ends.
Q: What is Shared Context ?
Shared Context: Context is a temporary area which 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 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.

Q: What are Batch Jobs in Mule ESB ?
A batch job is a top-level element in Mule which exists outside all Mule flows. Batch jobs split large messages into records which Mule processes asynchronously in a batch job; just as flows process messages, batch jobs process records.
A batch job contains one or more batch steps which, in turn, contain any number of message processors that act upon records as they move through the batch job. During batch processing, you can use record-level variables (recordVars) and MEL expressions to enrich, route or otherwise act upon records.


Q: What is Transient Context ?
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 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.
Q: What are the different endpoints available in Mule ESB ?
Different types of Endpoints are available in Mule, such as HTTP, JMS, IMAP, SMTP, and AJAX.

Q: How to check if file exists in Mule ESB ?
This can be done using Mule Expression Language(MEL) as follows-
        <when expression="#[xmlFileExists()]">

Q: What are Inbound endpoints and Outbound endpoints in Mule ESB ?
Inbound endpoints are message sources (, which as the name suggests is where messages are created. They can be created based on external events (like an incoming HTTP request or JMS message) or by polling (like files in a directory).
Outbound endpoints and anything else you see in a flow (except exception strategies) are message processors (, which means they do something with the message in-flight the flow.
Q: What is difference between Mule Connectors and Transports Mule ESB ?
Transports are targeted towards a way of transporting data, i.e. a protocol like HTTP or reading/writing files. These are general concepts and the other party behind such a data channel can be anything, a pure data sink or a party with whom data can be exchanged, own company or other.
Connectors are made for using specific APIs, e.g. those from or facebook. Usually, choosing a connector also determines how the data will be transferred in the end, e.g. HTTP.

See Also

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