Mule ESB Interview Questions
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 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.
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 end.
What are all the Primitives used in Mediation?
We have different types of primitives in mediation.
- Message Filter
- Type Filter
- Endpoint Lookup
- Service Invoke
- BO Map
- Message Element Setter
- DB lookup
- Data Handler
- Custom Mediation
- Header Setters
- Message Logger
- Even Emitter
- Sub Flow
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.
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.
What is Correlation Context?
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.
Difference between Callout and Service Invoke?
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.
How can you implement a loop in mediation?
By using Fan-in and Fan-out primitive.
What is the functionality of Fan-in and Fan-out?
Fan-out: We can use the Fan Out primitive to fire the output terminal once (with the input message) or to 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.
How can you change the runtime changes using mediation primitive?
We have future called Promotable properties in ESB. We can configure this future while development. Then we can make it changed at runtime without restarting the server it can be published.
What are all the configurations required for JDBC Adapter implementation?
Data Source needs to be created and need to configure with DB. If we have security, then need to created security authentication.
What is the Difference between SDO and SMO?
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
What is the Difference between Stop and fail?
Stop: Stops a particular path in the flow, without generating an exception.
Fail: Generates a failure in the flow.
Why am I getting ‘Unable to get resource from repository’ while building the Mule examples?
If you are getting this error message while building the Mule examples:
[WARNING] Unable to get resource from repository atlassian-m2-repository (http://repository.atlassian.com/maven2) Downloading: http://repository.atlassian.com/org.apache.maven.plugins/poms/maven-dependency-plugin-2.0-20060907.213033-3.pom [WARNING] Unable to get resource from repository atlassian-m1-repository (http://repository.atlassian.com) Downloading: http://repository.codehaus.org//org/apache/maven/plugins/maven-dependency-plugin/2.0-SNAPSHOT/maven-dependency-plugin-2.0-20060907.213033-3.pom [WARNING] Unable to get resource from repository Codehaus (http://repository.codehaus.org/) Downloading: http://snapshots.repository.codehaus.org/org/apache/maven/plugins/maven-dependency-plugin/2.0-SNAPSHOT/maven-dependency-plugin-2.0-20060907.213033-3.pom [WARNING] Unable to get resource from repository codehaus-snapshots (http://snapshots.repository.codehaus.org) [INFO] ------------------------------------------------------------------------ [ERROR] BUILD ERROR [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.
How to use Mule HQ with Mule?
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.
What is a Mule UMO?
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.
Mule won’t start? Check your Environment?
The java and mule environment variables must be setup correctly for 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_HOME\bin and MULE_HOME\bin 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 mule from loading.
How to add classes/jars to the Mule class path?
- Use the MULE_LIB variable (generally set in the run script)
- To include JAR file(s) in a mule class path, declare each dependent jar file in the MULE_LIB entry.
- For spring resource, if the XML bean declaration is placed within a project, include the project JAR file in the class path too (i.e., if not included, Mule will throw a **.xml not found on class path)
How to configure a simple FTP handler in Mule?
What is Mule Data Integrator?
Mule has released a data integrator tool, it is a visual mapping tool which 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 which sits on top of Mule ESB – this requires a license.
Where to find the class Abstract Mule TestCase?
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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