What exactly is Camel?
You want to try apache camel for the first time and get to know some key concepts?
This blog shall help you to get an idea what apache camel is and how to get started to write your own camel code.
The system landscape is getting more and more complex. Monolyths are getting replaced by microservices, which need to talk to each other. But the communication can be hard and tedious. For example there can be many different dataformats (JSON, XML, ZIP), protocolls (JMS, HTTP) and different technologies involved.
Apache Camel is an open-source integration framework that enables the integration of different systems and applications. It provides a consistent API for interacting with various protocols and technologies, making it easy for developers to connect systems and applications together. In this beginner tutorial, we will go over the basics of Apache Camel and how to get started with it.
Main concepts
Let’s look at the main concepts. Camel uses a routing engine, which is responsible for routing messages between different systems and applications. You can define your own routes to controll the message flow. To write these routes, camel integrates Enterprise Integration Patterns (EIP), which are best practices how to controll the message flow.
Camel also provides a set of components that can be used to interact with various protocols and technologies. These components can be used to connect to different systems, such as databases, message queues, file-systems and RESTful web services. Each component has its own set of options and configuration parameters that can be used to customize its behavior.
Get started
To get started with Camel, you will need to have a Java development environment set up and the corresponding camel-distribution (camel-core). The most easy start is via Spring-Boot or Quarkus, because then you only have to insert the camel-starter (e.g. for spring camel-spring-boot-starter) in your build-tool (maven or gradle) and you are ready to go. You can find here an example projekt. I always suggest using spring or quarkus initialiser to start a fresh new projekt (https://start.spring.io/, https://code.quarkus.io/)
A Camel route is defined using the Camel DSL, which is based on the EIP. Every camel-route will always start with „from“-part, which indicates the start of the route. It can have as many destination-endpoints as wanted (1-n relationship).
The „source“ and „destination“ are called endpoints. An endpoint is a URI that specifies where a message should be sent or received from. For example, an endpoint could be a JMS queue, a file system, or a RESTful web service.
In this example, the route takes messages from the „source“ endpoint and sends them to the „destination“ endpoint. The route can also include additional processing steps, such as filtering, transformation, and validation.
Here is an example of a route that reads messages from a JMS queue and writes them to a file:
In this example, the route takes messages from the „jms:queue:incomingMessages“ endpoint, which is a JMS queue, and sends them to the „file:output“ endpoint, which is a file system. The route also includes a processing step, which is implemented by the MessageProcessor class.
Camel also supports the use of processors, which are classes that can be used to perform additional processing on messages. A processor can be used to filter, transform, or validate messages before they are sent to their destination.
In this example, the MessageProcessor class is used to filter out messages that do not meet certain criteria
public class MessageProcessor implements Processor {
public void process(Exchange exchange) throws Exception {
String message = exchange.getIn().getBody(String.class);
if (message.contains("error")) {
exchange.getOut().setBody("Error: " + message);
} else {
exchange.getOut().setBody("Valid: " + message);
}
}
}In this example, the MessageProcessor class checks if a message contains the word „error“ and sets the body of the message accordingly. This can be useful when you want to filter out messages that do not meet certain criteria.
Camel also provides a powerful and flexible data transformation feature through its built-in Data Format component. This component allows you to convert data between different formats, such as JSON, XML, and CSV, using a simple and consistent API.
For example, you can use the Data Format component to convert a JSON message to an XML message, like this:
In this example, the unmarshal() method is used to convert the JSON message to a Java object, and the marshal() method is used to convert the Java object to an XML message.
Camel also provides built-in support for exception handling, which allows you to handle errors and exceptions in a consistent and reliable way. The ErrorHandler component allows you to define how errors and exceptions should be handled, and can be configured to send an email, log the error, or even trigger a JMS message.
Final Words
Apache Camel is a lightframe integration framework – Which is really powerfull. Easy routes from JMS to File can be written in minutes. And the conversion from JMS to File-Type is done in the core of camel, which makes it so attractive to use.
A link to an example github projekt can be found here