WebSphere ESB Interview Question and Answers

1. 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.

2. What are all the Primitives used in Mediation?

     We have different types of primitives in mediation.

1.      Message Filter

2.      Type Filter

3.      Endpoint Lookup

4.      Service Invoke

5.      Fan-out

6.      Fan-in

7.      XSLT

8.      BO Map

9.      Message Element Setter

10.  DB lookup

11.  Data Handler

12.  Custom Mediation

13.  Header Setters

14.  Message Logger

15.  Even Emitter

16.  Stop

17.  Fail

18.  Sub Flow

3. Difference between BO Map and XSLT?

     Both are used for manipulate and transfer the message.

Use XSLT when	Use BO Maps when
You have an existing stylesheet or want to use custom XSLT in the map.	You have an existing BO Map or submap.
You want to use XPath expressions inside the map.	You want to use the relationship service (particularly dynamic relationships).
You want to use Java snippets that use the DOM API to access or update data.	You want to use Java snippets that use the BO API (SDO API) to access or update data.
You want to use built-in XPath or EXSLT functions to access or modify data.	You want to order the completion sequence for the transforms.
You want to combine contents from more than one array (repeating element).	BO Maps can be faster when used with WebSphere® Adapters, because the BO Maps work directly with the SDO API.

Performance with XSLT or BO Maps depends on a number of factors including:

• An XSLT map is fastest when processing web services messages and the incoming data is unmodified between the entrance to the mediation flow and the XSLT primitive.
• A BO map can be faster when the message content has already been accessed in the mediation flow.

4. What is SMO? And wt it contains?

     The SMO model is a pattern for using SDO Data Objects to represent messages. The SMO contains a representation of the following groups of data:

• The business payload of the message. The payload is the application data exchanged between service endpoints.
• Header information associated with the message. For example, Java Message Service (JMS) headers if a message have been conveyed using the JMS API.
• Context information (data other than the message payload).

5. What are Shared, Transient and Correlation 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.

      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.

     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.

6. 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.

o        If the call is successful, the Callout Response node in the response flow receives the response message.

o        If the call is unsuccessful, the Callout can be set to retry service invocations depending on the type of fault received.

7. How can you implement loop in mediation?

     By using Fan-in and Fan-out primitive.

8. 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. 

9. 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.

10. What are all the configurations required for JDBC Adapter implementation?

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

11. Different 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

12. Difference between Stop and fail?

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

            Fail: Generates a failure in the flow.