Apache Camel Interview Questions

Apache Camel Interview Questions | Freshers & Experienced

  • Subrata Dutta
  • 12th Apr, 2021
  • 586 Followers

Key Features of Apache Camel

Below are few major features of Apache Camel

Open source framework

Pluggable data formats

POJO model

Message-oriented middleware

Ease of testing

Eclipse based tooling

Type converters for marshaling and unmarshalling

100+ Components

Message Exchange Patterns

Apache Camel Interview Questions

Q1. What is Apache Camel?

Apache Camel is used to integrating the EIP. Companies really have a lot of data exchange daily and for that purpose, even multiple applications are integrated. This is simply done to make the process in a standard format. It is an open-source framework for message-oriented operations. It is basically the implementation of the Enterprise integration patterns (EIP), to the Java code. It simplifies the method of the complex integration process.

Q2. What are routes in Apache Camel?

The Route in the Apache Camel is one of the main building blocks that is used to contain flow and integration logic. You can specify sources and the endpoint of the route using the DSL. The transformations that need to be taken place during the routing can also be defined in the route. The URI’s to receive data from different sources can also be denied in the route.

The route can be configured by extending the RouteBuilder class and overriding the configure() method. The from() and to() method is used inside the configure() method to define the sources and endpoint of the routing.

//example of routing using RouteBuilder class
Public class MyRouteBuilder extends RouteBuilder{ @Override Public void configure() throws Exception { //define your route } }

Q3. What is EIP in Apache Camel?

The integration of applications for the data exchanges that take place in a company is really complex. For that purpose, the enterprise integration patterns (EIP), has become the best and standard method to practice in this case. The Apache Camel just uses to implement this EIP’s to the Java code that too really easily and with great simplicity. It is really helpful for the developers with its rule-based routing and also the mediation engine.

Q4. What is Seda in camel?

It is known as the Stage event-driven architecture (SEDA). This basically divides the workflow into stages and then it just follows the queue so that the load is not on the single area. This also makes the task easy and simple to complete. It is also fast in response. It allows you to join routes or say multiple routes using the simple queue. It is a very simple replacement option for the JMS queues.

Q5. What is Processor in Apache Camel?

Here, with the help of this processor, you get complete access to the exchange process or the message exchange that takes place. It allows you to write in the routes of the camel and also you can reuse the existing file. Also, the custom message processors also provide you with a platform where you can just do anything while working on Java. Herewith the help of this processor the message translator and also the consumer message exchange both can be implemented.

Q6. What are DSLs in Apache Camel?

It is basically a language that is used in Java known as the Domain-specific language (DSL). It just helps you to create the EIP or routes and used in any domain-specific language. It is designed for certain specific tasks.

  • Java DSL: Here it basically uses the developer’s style. It is a Java-based DSL.
  • Blueprint XML: It is an XML based DSL and it follows the OSGi Blueprint XML files.

Q7. How to rollback transaction in Apache Camel DSL?

Q8. Enlist few good uses for Apache Camel?

Q9. What is CamelContext?

Q10. What is RouterContext?

The router context is the tag that is used to define routes outside the <camelcontext/> tag in XML. A new route can be defined by the <routeContext/> tag. The definition of the route that is created in the <routeContext/> tag can be reused by different <camelContext/>. But at runtime, the camel context will create its own route instance based on the definition.

Q11. What is registry in Apache Camel?

Camel registries are basically used to locate the existing files. The beans that are used in the Camel routes are basically used for using the existing components that are already present in the routes. It is better to use a lightweight and at the same time simple programming tools in the camel routes. So in this all process it is necessary to register the beans initially that will help you anytime to locate your file and with camel, the registry is already done automatically.

Q12. What is name of default registry in Apache Camel?

Q13. Enlist the error handlers provided by Apache Camel?

Q14. What is use of stream component in Apache Camel?

Q15. What Is Camel Exchange?

Camel Exchange is the messaging process of exchanging messages which involves a request message and its corresponding reply or an exception message. It allows you to send the message and can also receive the reply to the same. It has a unique ID that gives you permission for the exchange. It also has a pattern called the MEP which just can denote you whether you can just send the message or can reply also using the InOnly like for example the JMS messaging and the InOut messaging like the HTTP based transports.

Q16. What are components in Apache Camel?

The component in Apache Camel is the factory that is used to model the endpoint of the message channels that either consume or send a message. The component can be created by implementing the org.apache.camel.Component by a class.

Some of the pre-built components in the Camel are,

  • Bean – It invokes Java bean in the registry.
  • Direct – It is used to synchronously call other endpoints.
  • File – It is used to read or write to a file.
  • Log – It is used to log messages.
  • Mock – It tests the messages that flow through the route.
  • SEDA – It is used to asynchronously call another endpoint.
  • Timer – It sends a message at regular intervals in the route.

Q17. How to pass data between the routes in Apache Camel?

The data can be passed between thee endpoints using the routes. You need to define the from and to location and use RouteBuilder to define the route in Java DSL. The source of the route starts at one point and ends at one or more points. Between the two endpoints, you need to define the processing logic using the configure method.

//example of route creation with the source and endpoints for passing data
context.addRoutes(new RouteBuilder() {
  @Override
  public void configure() throws Exception {
     from("direct:DistributeOrderDSL")
     .to("stream:out");
  }
}

Q18. What is a camel context?

The Camel context in the Apache camel is the loading container of all the resources that are required for the execution of the routing. It is the runtime system. It provides all the resources and access to all other services in the Apache camel. The different resources in the camel context are type converters, registry, components, endpoints, routes, data formats, and languages.

These resources in the context allow the user to execute the routing logic. It is described by org.apache.camel.CamelContext interface.

Q19. How does Apache Camel work with ActiveMQ?

The ActiveMQ component is used to embed Apache Camel inside the ActiveMQ broker. It provides good flexibility in extending the message broker. The ActiveMQ component also avoids the serialization and network cost of connecting to ActiveMQ remotely.

This component is based on the JMS component and allows the messages to be sent or consumed using the JMS Queue.

Q20. How do I disable JMX in Apache Camel?

The JMX instrumentation agent is enabled in Camel by default. To disable the JMX instrumentation agent, set the following property in the Java VM system property,

Dorg.apache.camel.jmx.disabled=true

Another way of disabling is by adding the JMX agent element inside the camel context element in the Spring configuration,

<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring">
 <jmxAgent id="agent" disabled="true"/>
   ...
</camelContext>

Q21. How to restart CamelContext?

The camel context provides different methods like start, stop, suspend, resume to control the camel lifecycle. Restarting a service can be achieved by using two different methods. One is using stop the context and then starting the context. It is called cold restart and it makes all the endpoints obsolete by clearing the internal state, cache, etc. Another method is by using suspend and resume operations. It keeps all the endpoints, so you can use them after restarting.

Q22. How to enable debug logging in Apache Camel?

To enable the debug logging, the log4j is used. Then, enable the DEBUG level logging in the log4j property file for the org.apache.camel package. To enable the debugging in the log4j.properties file add the following line.

log4j.logger.org.apache.camel = DEBUG

About Author :

  • Author of Apache Camel Interview Questions

    Subrata Dutta

    Subrata Dutta is IT Project Manager from Noida, Uttar Pradesh, India. He is an exceptional team player who is proactive, efficient, methodical and has strong interpersonal & people management skills.

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