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Apache Camel Interview Questions and Answers

Ques 1. What is Apache Camel?

In an enterprise, a number of systems of different types exist. Some of these may be legacy systems while some may be new. These systems often interact with each other, and need to be integrated according to the requirements. This interaction or integration is not easy as the implementations of the systems, their message formats may differ. One way to achieve this is to implement code which bridges these differences (message transformation, rules to integrate, validations etc). However this will be point to point integration. If tomorrow again if there is change in a system the other might also have to be changed which is not good. Instead of this point to point integration which causes tight coupling we can implement an additional layer to mediate the differences between the systems. This results in loose coupling and not affect much our existing systems. Apache Camel is a rule-based routing and mediation engine that provides a Java object- based implementation of the Enterprise Integration Patterns using an API (or declarative Java Domain Specific Language) to configure routing and mediation rules.

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Ques 2. What are routes in Apache Camel?

The core functionality of Apache Camel is its routing engine. It allocates messages based on the related routes. A route contains flow and integration logic. It is implemented using EIPs (Enterprise Integration Patterns) and a specific DSL (Domain Specific Language).

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Ques 3. What are DSLs and which DSLs have you used?

Routes in a variety of domain-specific languages (DSL). The most popular ones are: 

  • Java DSL: A Java based DSL using the fluent builder style. 
  • Spring XML: A XML based DSL in Spring XML files

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Ques 4. What are EIPs in Apache Camel?

EIPs stand for Enterprise Integration Pattern. These are Design patterns for the use of enterprise application integration and message-oriented middleware in the form of a pattern. Various EIPs are used in Apache Camel. Some of them are: 

  • Splitter Pattern: Split the data on the basis of some token and then process it. 
  • Content Based Router: The Content-Based Router inspects the content of a message and routes it to another channel based on the content of the message. Using such a router enables the message producer to send messages to a single channel and leave it to the Content-Based Router to inspect messages and route them to the proper destination. This alleviates the sending application from this task and avoids coupling the message producer to specific destination channels. 
  • Message Filter: A Message Filter is a special form of a Content-Based Router. It examines the message content and passes the message to another channel if the message content matches certain criteria. Otherwise, it discards the message.
  • Recipient List: A Content-Based Router allows us to route a message to the correct system based on message content. This process is transparent to the original sender in the sense that the originator simply sends the message to a channel, where the router picks it up and takes care of everything. 
  • Wire Tap: Wire Tap allows you to route messages to a separate location while they are being forwarded to the ultimate destination.

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Ques 5. What is an exchange in Apache camel?

The message to be routed in Camel route is present in the Exchange. It is the message holder. Apache camel uses Message Exchange Patterns(MEP). Apache camel exchange can hold any kind of message. It supports a variety of formats like XML, JSON etc.

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