Apache Camel interview Questions and Answers

Apache camel interview questions.

1. What is Apache Camel ? 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. To better understand what is apache camel, lets first understand what are Enterprise Applications and Enterprise Integration Patterns.

2. How to implement Error Handling using Apache Camel ? Error handling in Camel can roughly be separated into two distinct types:non transactional Transactional What is a Message in Apache Camel ? Message implements the Message pattern and represents an inbound or outbound message as part of an Exchange.It contains the data being transferred using Routes- It consists of the following fields-Unique Identifier Headers Body Fault Flag

3. What is an exchange in Apache Camel ? Camel Exchange represents an abstraction for an exchange of messages which involves a request message and its corresponding reply or an exception message. It consists of-Exchange ID Message Exchange Pattern InOnly message InOut message Exception Properties How to read data from queues using Apache Camel ? We make use of Apache Camel JMS Component. We will be reading from one JMS Queue and sending the message to another jms queue. Also we will be making use of ActiveMQ queues.

4. What are Components in Apache Camel ? Component  act as an endpoint factory using which we can interact with external systems. Camel provides a large number of components using which we can interact with externals systems. For example here we have to transfer files from one folder to another, so we make use of the file component at both the end of the message channel. What is CamelContext ? We cannot run our Camel Application only using the route. We also need the camel context which acts as a runtime system that runs and manages the routes. It is responsible for all managing all aspects of a route. What is Quartz Library? How to use it with Apache Camel Quartz is a richly featured, open source job scheduling library that can be integrated within virtually any Java application - from the smallest stand-alone application to the largest e-commerce system.

5. How to implement Exception Handling in Apache Camel ? Using Apache Camel Exception Handling can be implemented using-Using Do Try Catch Block Using OnException Block Enlist few good uses for Apache Camel? Apache Camel  is a good choice when you want to integrate several applications with different protocols and technologies. You can use it with Java, Scala, Groovy or Spring XML. What is Processor in Apache Camel? Processor is Apache Camel  is an interface that is used to implement consumers of message exchanges or Message Translator.

6. What are Components in Apache Camel? A  Component in Apache Camel  is a factory or collection of Endpoint instances. We can configure Component instances explicitly and add them to a CamelContext in an IoC container like Spring or Guice . Components can be auto-discovered using URIs. Apache Camel provides numerous pre-built components. Below we have listed some important Camel components from the core module. Bean Direct File Log SEDA Timer

7. What are routes in Apache Camel? Routes plays  a critical role in Apache Camel. The application flow and logic are specified here.In Camel we can define routing rules using a Java DSL. How to rollback transaction in Apache Camel DSL? To rollback transaction in  Apache Camel DS L, you can perform the following steps: Remove Spring transaction manager. Remove Spring transaction policy. Remove transacted() from Camel route. What Are Eips In Apache Camel? EIPS (ENTERPRISE INTEGRATION PATTERNS)  is an architectural design pattern that defines code-agnostic workflows for common business tasks.

8. What is Messaging? Messaging is a communication mechanism used for system interactions. In software development messaging enables distributed communication that is loosely coupled. A messaging client can send messages to, and receive messages from, any other client.  What is Advanced Message Queuing Protocol (AMQP) ? The Advanced Message Queuing Protocol (AMQP) is an open standard application layer protocol for message-oriented middleware. AMQP 0-9-1 is a binary messaging protocol and semantic framework for microservices and enterprise messaging.

9.   How to start the execution of routes Apache Camel? To start the execution of routes Apache Camel, you can perform the following steps: Create a CamelContext . Optionally, configure components or endpoints. Add whatever routing rules you wish using the DSL and RouteBuilder or using XML DSL. Start the Camel context. 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 What is an ESB? Have you deployed camel on any ESB? ESB stands for Enterprise Service Bus. It can be defined as a tool designed to help implement an application using SOA principles Not for all projects projects is the use of ESB an optimum solution ESB should be used when projects involve integrating a number of Endpoints like Webservices, JMS, FTP etc. Have deployed JBoss Fuse ESB for Apache Camel Deployement .

10. Apache camel Kafka It is basically an open-source framework. It basically or mainly focuses on making things easier. Also, they make the integration process very simple and sorted for the developers. It has a very unique design messaging system. It is a log service that is distributed and partitioned. It basically focuses on enterprise integration patterns. Also, it is really and highly configurable. It has a very high and reliable performance efficiency. Also, it is really scalable. What is basic differences between Apache Camel and Kafka?

11. What are endpoints in apache camel? Camel supports the Message Endpoint pattern using the Endpoint interface. Endpoints are usually created by a Component and Endpoints are usually referred to in the DSL via their URIs. What are various components in apache camel? Which ones have you used? Apache camel provides us with a number of components. These components make interacting create endpoints with which a system can interact with other external systems. For example using an ActiveMQ component we expose an ActiveMQ endpoint for interaction with external system. There are more than 100 components provided by Apache Camel. Some of them are FTP,JMX, Webservices, HTTP. Apache camel also allows users to create custom components.

12. How are exception handled using Apache Camel? Exception can be handled using the <try> <catch> block, < OnException > block or the < errorHandler > block. The errorHandler is used to handle any uncaught Exception that gets thrown during the routing and processing of a message. Conversely, onException is used to handle specific Exception types when they are thrown. 

13. What is Redelivery policy in Apache Camel? A redelivery policy defines rules when Camel Error Handler perform redelivery attempts. For example you can setup rules that state how many times to try redelivery, and the delay in between attempts, and so forth. What is RouterContext ? It is now possible to define routes outside < camelContext /> which you do in a new < routeContext /> tag. The routes defined in < routeContext /> can be reused by multiple < camelContext />. However its only the definition which is reused. At runtime each CamelContext will create its own instance of the route based on the definition.

14. What is Apache Camel Idempotent Consumer pattern? In Apache Camel we use the Idempotent Consumer pattern to filter out duplicate messages. Consider a scenario where we have to process files only once. If there are any duplicates they should be skipped. Using Apache Camel we can use Idempotent Consumer directly within the component so it will skip files that are processed once. This feature is be enabled by setting the idempotent=true option. In order to achieve this Apache Camel keeps track of the consumed files using a message id which is stored in the repository called Idempotent Repository. Apache Camel provides the following types of IdempotentRepository .

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