Apache Camel: An Integration Framework

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What is Apache Camel

Apache Camel is an open source integration framework designed to make integrating systems simple and easy. It allows end users to integrate various systems using the same API, providing support for multiple protocols and data types, while being extensible and allowing the introduction of custom protocols.

 Domain-Specific Language

Routes and routing engine are the central part of Camel. Routes contain the flow and logic of integration between different systems.

In order to define routes more easy and clean, Camel offers several different domain-specific languages (DSL) for programming languages like Java or Groovy. On the other hand, it also provides defining routes in XML with Spring DSL.

Using either Java DSL or Spring DSL is mostly user preference, as most of the features are available in both.Java DSL offers a bit more features which are not supported in Spring DSL. However, Spring DSL is sometimes more beneficial as XML can be changed without the need to recompile the code.

Four Approaches to Application Integration

There are four application integration approaches with each approach addressing some of the integration guidelines better than others. The four integration approaches include File Transfer, Shared Database, Messaging, and Remote Procedure Invocation. Here is a brief explanation of each one:

• File Transfer: One application produces files of shared data for others to consume, and vice versa.
• Shared Database: Applications can store the data they wish to share in a common database.
• Messaging: An application connects to a shared messaging system, exchanges data, and invokes behavior using messages.
• Remote Procedure Invocation: An application exposes its APIs so that they can be invoked remotely by other applications to run its behavior and exchange data.

Apache Camel Architecture

• Message contains data which is being transferred to a route. Each message has a unique identifier and it’s constructed out of a body, headers, and attachments
• Exchange is the container of a message and it is created when a message is received by a consumer during the routing process. Exchange allows different types of interaction between systems – it can define a one-way message or a request-response message
• Endpoint is a channel through which system can receive or send a message. It can refer to a web service URI, queue URI, file, email address, etc
• Component acts as an endpoint factory. To put it simply, components offer an interface to different technologies using the same approach and syntax. Camel already supports a lot of components in its DSLs for almost every possible technology, but it also gives the ability for writing custom components
• Processor is a simple Java interface which is used to add custom integration logic to a route. It contains a single process method used to preform custom business logic on a message received by a consumer

At a high level, the architecture of Camel is simple. CamelContext represents the Camel runtime system and it wires different concepts such as routes, components or endpoints.

3. Maven Dependencies

In order to use Camel, we need to first add the Maven dependency:

<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-core</artifactId>
    <version>2.18.0</version>
</dependency>

Why Apache Camel?

We have so many integration frameworks in the software market, open-sourced, and licensed. Out of all, the Apache Camel integration framework is one of the best open-source software, having a rich set of features. Using these features, we can develop loosely coupled applications with ease.

Features:

Apache Camel provides the following features.

1. Light-weight Open Source
2. Easy Configuration
3. Routing and Mediation Engine
4. Payload-agnostic router
5. A domain-specific language (DSL) and POJO Model
6. Enterprise integration patterns (EIPs)

Conclusion

Apache Camel is an excellent framework for integrating applications with different technologies and protocols. The best part — besides exceptional support for various technologies — is that we can always use the same concepts. It also has excellent error handling and automatic testing that make it optimal for specific integration projects.