Apache Camel Interview Questions

Apache Camel is an open-source integration framework. Mainly, it is a message-based middleware that works only based on rules. Apache Camel's rule-based engine handles accepting, processing, and delivering messages to destinations. With Apache Camel, you can quickly connect to various applications and systems and pass information.

Apache Camel is a popular messaging middleware widely used by many companies. So there is an ever-growing demand for professionals who are experts in Apache Camel. MindMajix content team has curated these top 50 Apache Camel interview questions and answers in three categories to help the aspirants of Apache Camel. You can go directly to the relevant questions and answers based on your expertise.

• For Freshers  
• Intermediate 
• Advanced Learners
• Apache Camel FAQs
• Tips
• Conclusion

Top 10 Frequently Asked Apache Camel Interview Questions

1. What is Apache Camel?
2. What are the uses of Apache Camel?
3. How is Apache Camel different from Apache Kafka?
4. What are the pros and cons of Apache Camel?
5. How will you roll back a transaction in Camel DSL?
6. Can we use REST API with Apache Camel?
7. What are the various JAR files used in Apache Camel?
8. Compare Apache Camel with Spring Integration
9. Can we use Apache Camel with Java Spring?
10. What are the different ways to define routing rules in Apache Camel?

Apache Camel Interview Questions For Freshers 

1. What is Apache Camel?

Apache Camel is an open-source, lightweight, and integrated framework. It works based on enterprise integration patterns. It is a rule-based routing engine that uses Domain Specific Languages (DSL) to configure routing rules. The DSLs can be Java, YAML, Groovy,  etc. It is an integration tool that smoothly integrates with many applications. Moreover, Apache Camel offers a lot of components to create routes so we can process messages efficiently.

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2. Explain: Components in Apache Camel.

A component is a collection of endpoint instances. We can configure components and add them in a CamelContext in an IoC container. Not only that, we can auto-discover the components using URIs.

3. Mention the various components used in Camel.

File, JMS, HTTP, ActiveMQ, Bean, SEDA, Log, and FTP are a few components used in Apache Camel. These components are used to connect with external systems. No wonder you can create custom components using Apache Camel.

Below is the use of a few components of Apache Camel.

File: we can use this component to read and write files.

HTTP: we can use this component to send and receive HTTPS requests

JMS: we can use this component to send and receive messages from a JMS component.

4. What are the uses of Apache Camel?

 Following are a few uses of Apache Camel.

• It is used to integrate with many applications
• It supports DSLs such as Groovy, Java, etc.
• It is used to transform messages from one format to another
• It is used to route messages from a JMS queue to file systems
• It easily handles the complexities of codes

5. What are the key features of Apache Camel?

Here are the key features of apache camel.

• Apache Camel is a lightweight integration framework
• It is easy to use and scale
• It supports over 50 data formats
• It handles errors automatically
• It comes with robust redelivery policies
• It can manage complex aggregations
• It can run anywhere – on-premises or cloud
• It can be embedded as a library within spring boot as well as application servers.
• It comes with many components used to access APIs, Databases, etc.
• It can process streaming as well as event-based messages seamlessly
• It supports various Enterprises Integration Patterns (EIPs)and protocols

6. How is Apache Camel different from Apache Kafka?

Apache Camel	Apache Kafka
It is an open-source integration framework	It is a distributed messaging system
It is an integration tool. So it simplifies integrating with other tools and applications.	It is a message queuing tool. It offers a unique messaging system.
It is used for application integration, message transfer, pattern-based development, etc.	In a way, Kafka is a log service. It is used for log commits, stream processing, and so on.
It is highly configurable.	It is highly scalable and reliable.

7. What do you mean by EIPs in Apache Camel?

EIP stands for Enterprise Integration Patterns. They help to resolve integration issues. Apache Camel uses many EIPs and resolves many integration problems.

8. What do you mean by a processor in Apache Camel?

A processor is nothing but a node that exists in the routing of Apache Camel. It is an essential building block of Apache Camel. Generally, processors create, use, and change exchanges. And the exchanges flow from one processor to another with the support of endpoints as well as components.

9. What do you understand by message in Apache Camel?

A message in Apache Camel contains a header, body, and also attachments. The header contains information about the sender, content encoding, as well as authentication. The body includes the raw data or, in other words, the payload. Attachments are the extra information and are optional.

10. What do you mean by Exchange in Apache Camel?

An exchange in Apache Camel is a message holder. It carries the message that it is routed in the Apache Camel route. It includes the request message as well as the corresponding reply message. An exchange consists of many elements such as exchange ID, ‘InOnly’ message, message exchange pattern, exception, ‘InOut’ message, and properties. It doesn't matter whether it is a JSON or XML – Apache Camel supports any message since it uses the Message Exchange Pattern (MEP).

11. Describe Routes in Camel

A route in the Apache channel is a message channel connecting two endpoints together. One endpoint is the produced message, and another is the consumed message. Every route has a flow as well as integration logic. It is essential to note that you can implement routes using EIPs and DSLs.

12. Describe: CamelContext?

CamelContext is highly important in Apache Camel since routing is not just enough to pass messages. We need features like CamelContext to perform routing effectively. Essentially, CamelContext is the runtime system used to execute routes. It contains all the elements connected with a route, such as type converters, endpoints, data formats, languages, etc.

13. What do you understand by ESB?

 ESB is the short form of Enterprise Service Bus. It is the tool used to implement applications using SOA principles. For example, JBoss Fuse ESB can be used for Apache Camel deployment. It would be best to use ESB when using endpoints such as FTP, Webservices, etc.

14. What do you mean by Endpoints?

Components in Apache Camel generally create endpoints. They indicate the destinations of messages. 

15. List the different types of routing used in Apache Camel.

Following are the different routing used in Apache Camel.

• Content-based Routing
• Multicast Routing
• Recipient list Routing
• Static Routing
• Dynamic Routing
• Template Routing

16. What do you mean by DSLs?

DSL stands for Domain Specific Languages. Java DSL, as well as Spring XML, are the two widely used DSLs.

Related Article: Top XML Interview Questions And Answers

17. What do you understand about the Idempotent Consumer Pattern in Apache Camel?

We generally use the idempotent consumer pattern to remove duplicate data. In other words, it acts as a message filter to remove duplicate patterns. As a result, we can avoid consuming the same message multiple times.

18. Why is Apache Camel known as a routing framework?

 Apache Camel receives messages from one endpoint and sends them to another endpoint. This is done with the help of EIPs. A typical route or router may consist of an event-driven consumer along with a polling consumer. Besides, there can be more than one processor instance that will help send messages to endpoints.

19. What platforms does Apache Camel support?

 Apache Camel supports the following platforms:

• Apache Camel 2. x supports the platform JDK 8
• Apache Camel 3. x supports the platform JDK 8 
• Apache Camel 3. x supports the platform JDK 11

20. What are the pros and cons of Apache Camel?

 Pros

• In Apache camel, rules drive efficient routing between sender and receiver.
• It is an easy and reliable integration framework
• We can quickly transform messages
• It comes with efficient testing tools

Cons

• It lacks a graphical user interface
• The learning curve is very steep
• Integration with big data is not good
• Deployment is a bit hard.

Intermediate Apache Camel Interview Questions

21. How will you roll back a transaction in Camel DSL?

If you want to roll back the transaction in a camel DSL, you need to follow the below steps:

• First, you need to remove the Spring rollback manager
• Next, you need to remove the Spring transaction policy
• Finally, you can remove the transacted ( ) from the Apache Camel route.

22. What are the different message exchange patterns of Apache Camel?

 There are two types of message exchange patterns used in Apache Camel as follows:

• Event message
• Request reply

23. How can you perform exception handling in Apache Camel?

In Apache Camel, the exception handling can be performed in two ways as follows:

• Using Do Try Block: This block is similar to the ‘Java Try Catch block in many ways. 
• Using OnException Block:  This block is written as a separate block. So the exception will be caught immediately, and messages will stop retrying. 

 It is essential to note that we can use the spring configuration file to write codes for exception handling in Apache Camel. Besides, we can use Java DSL for writing codes for exception handling.

24. Can we make database calls using Apache Camel?

 Yes. We can make database calls using Apache Camel. For instance, we use SQL queries to fetch from /update data into MySQL tables. Similarly, we can connect with Oracle database procedure with Apache Camel. You can perform this with the support of Spring Boot.

25. Can we use REST API with Apache Camel?

Yes. We can use REST API with Apache Camel because Apache Camel provides a REST-styled DSL. It allows end-users to use REST services using GET, DELETE, and POST statements. We can use various camel components such as camel-rest, camel-jetty, camel-netty-http, camel servlet, camel-platform-HTTP, and camel undertow in this regard.

26. Can we integrate a database with Apache Camel?

Yes. We can integrate a database with Apache Camel. We can connect camel with the Postgres database using the JDBC driver. Also, we can use JDBC queries to connect with databases.

27. What do you understand by the Redelivery Policy?

The redelivery policy includes rules to direct the Apache Camel Error Handler. We can apply the rules when the error handler attempts to redeliver messages. For example, you can set up rules such as the maximum number of attempts allowed to redeliver messages, the delay between the successive attempts, and so on.

28. Can we use Apache Camel with Spring Boot?

Yes. We can use Apache Camel with Spring Boot. Spring Boot helps to configure Apache Camel automatically. Also, it helps to identify the spring routes. Besides, it uses Camel components such as producer templates and type converters as Java Beans.

29. How will you execute JUnit test cases for Apache Camel?

 Apache Camel executes test cases with the support of many endpoints such as Mock, Dataset test, and Dataset. We can use Camel spring test support to perform JUnit tests.

30. What are the different Message Exchange Patterns (MEPs) used in Apache Camel?

There are two types of MEPs used in Apache Camel. They are ‘In Only’ and ‘In Out’. When it comes to ‘In Only’, users create an MEP that uses the ‘In Only’ message. When it comes to ‘In Out’, users create a synchronous pattern that contains the caller’s response message.

31. Why do we connect Apache Camel with ActiveMQ?

We connect Apache Camel with the message broker ActiveMQ to create powerful message-based applications. As a result, these applications can manage any message format and protocols effortlessly. Also, we can achieve POM dependency and build the camel route to read and write messages from ActiveMQ. 

32. What are the various JAR files used in Apache Camel?

The following are the JAR files used in Apache Camel. They are listed below:

• Camel-api
• Camel-cloud
• Camel-base
• Camel Management API
• Camel-jaxp
• Camel util

33. What do you mean by Event-Driven consumer in Apache Camel?

Essentially, an event-driven consumer is a type of consumer. This customer receives messages from a producer, processes the messages, and then finally sends the messages to a destination. 

34. At what levels, Apache Camel is configured?

Apache Camel is configured at two levels:

• Component level
• Endpoint level

35. When can you restart a CamelContext?

We can restart a CamelContext when it is deployed on a server. Restarting a CamelContext can be done in two ways. In one way, you can stop the context and then start the context. It is known as a cold restart. Another way is to suspend the operations and then resume the operations later. Note that all the endpoints become obsolete in the cold restart, whereas endpoints are kept at the same level in the latter.

Advanced Learners Apache Camel Interview Questions

36. How can you enable and disable Apache Camel JMX?

 We can enable Apache Camel JMX by including the Apache Camel management JAR file in the classpath. If you want to remove the JMX file, then you need to remove the JAR file from the classpath.

 You can disable JMX from the CamelContext using the below codes:                         

37. How will you enable debug logging in Apache Camel?

We can use log4j for logging files to enable debug logging. And then, we need to ensure that the  log4j.properties file triggers debug-level logging. This is to be done for the org.apache.camel package.

38. How can you pass data between the routes?

You can pass data between the routes using an object, as shown below.

39. How can you create a new default exchange in Apache Camel?

We can use create a new default exchange using the below codes.

40.  What is the use of the Quartz component in Apache Camel?

Quartz is nothing but a job-scheduling library. It helps to connect with any java application. With this component, you can easily schedule the delivery of messages. You can also use Apache Camel to start a job at the scheduled time every day.

41. Compare Apache Camel with Spring Integration

Apache Camel	Spring Batch
It makes integration simpler	It enables the development of batch applications
Spring boot, as well as Quarkus, integrate with Apache Camel	Spring boot, as well as MongoDB, integrates with spring batch.

42. What is the key difference between Apache Camel and Fuse Mediation Router?

Apache Camel is an open-source and lightweight framework. On the other hand, Fuse Mediation Router is a robust as well as feature-rich tool.

43. What will happen if a processor throws an exception while running inside an Apache CamelContext?

If a processor throws an exception, the route's error handler will be invoked immediately. The error handler's role is to try to rectify the error and continue message processing. If the error handler cannot solve the error, it will stop the route and intimate the details to the caller.

44. Can we use Apache Camel with Java Spring?

Yes. We can use Apache Camel with Java Spring. As a result, it allows using the features such as transaction management, spring dependency injection, etc.

45. How will you use SOAP services in Apache Camel?

 Apache Camel uses two components to work with SOAP services. The components are the CXF component and SOAP data format. The CXF component acts as the wrapper for Apache CXF. For example, you can use the CXF component to send messages to a SOAP service as well as receive messages from a SOAP service.

 Another one, the SOAP component, is a data format used to read and write SOAP messages.

46. How to configure a component in Apache Camel?

 If you want to configure a component in Apache Camel, you need to follow the below steps:

• First, create an instance of the component.
• Set properties for the component.
• Finally, add the component to the Apache Camel's bean factory.

 For example, consider the JMS component. If you want to configure the component, first create the instance as jms = new JmsComponent (). And then set the property of the component as jam.SetConnectionFactory ().

47. What is the use of a Content-Based Router?

This router in Apache Camel processes messages based on their content.

48. What are the different ways to define routing rules in Apache Camel?

We can define routing rules in the following two ways.

• Java-based DSL
• Spring XML configuration format.

49. What are the different error-handling methods applied in Camel?

Following are the two error-handling methods used in Camel.

• Transactional
• Non-transactional

50. How can you read messages from queues with Camel?

We can read messages using the JMS component. It means we can read a message from one JMS queue and send it to another. Besides, we can use the ActiveMQ queues.

Apache Camel FAQs

1. What is Apache Camel?

Apache Camel is an open-source and integration framework. This framework integrates with any application or tool seamlessly. Apache Camel is also a platform that transports messages using various protocols and procedures.

2. What is a processor in Apache Camel?

A processor is a node that exists in the routing of Apache Camel. Processors can generate, use, and modify exchanges. Usually, exchanges flow from one processor to another with the support of endpoints and components.

3. What are the routes in Apache Camel?

A route in the Apache channel is a message channel that connects two endpoints. One endpoint is the produce message, and another is the consume message. Know that every route in Apache Camel has a flow and integration logic. By using EIPs as well as DSLs, we can implement routes.

4.  What do you mean by the exchange in Camel?

An exchange in Apache Camel is a message holder. It carries the message that it is routed in the Apache Camel route. It has the request message as well as the respective reply message. Apache Camel supports any type of message – JSON or XML.

5. How is Apache Camel different from Mulesoft?

Although both tools are the same in terms of open source, they differ in their implementation. Apache Camel has a vast community, so implementation and development are easy. On the other hand, implementing Mulesoft requires the dedicated support of professionals. Moreover, both tools have different architectures and interfaces.

6. Is Apache Camel an ETL?

Yes. Apache Camel is an ETL tool. It supports many integration platforms that create and process data.

7. Is Apache Camel got outdated?

No. A large community is still using it. This is because it simplifies integration remarkably.

Tips to attend Apache Camel interview

Here are a few tips to successfully clear your Apache Camel interview.

• Sharpen your Knowledge

As you know, if you want to win a battle in a short time, you need to sharpen your sword for a long time. Likewise, you must learn the Apache Camel concepts and applications thoroughly. It will help to crack your Apache Camel interview in no time. Simply put, prepare all the topics of Apache Camel completely.

• Research the Interview Questions

You must research the possible questions that may come up during the interview. Read this blog thoroughly to equip yourself to face the Apache Camel questions. Not only that, you can frame your own questions and find solutions. It will help to ease your interview.

• Take support from all Sources

If you have any doubts or need clarifications, you shouldn’t hesitate to ask your colleagues, friends, and mentors. Collecting various materials from multiple sources will help you to enhance your Knowledge. In short, you must be willing to acquire Knowledge from every source.

• Show your Analytical Skills

Nowadays, it is highly expected from employers that every employee should have good analytical skills. This is because challenges may arise at any time in any project. So you must be willing to face challenges and solve them quickly with your analytical skills.

Conclusion

It's time to conclude! Apache Camel is a lightweight integration framework that integrates seamlessly with many platforms and applications. Apache Camel has a routing engine that receives messages, processes them, and sends them to destinations. Simply put, Apache Camel simplifies integration solutions. We hope all these top 50 Apache Camel interview questions and answers must have helped you prepare for your interview. If you want to learn more about Apache Camel, you can sign up for a course in MindMajix. This certification will help you to enrich your Knowledge of Apache Camel and crack your interview easily.