面试题与答案

In an enterprise, a number of systems of different types exist. Some of these may be legacy systems while some may be new. These systems often interact with each other, and need to be integrated according to the requirements. This interaction or integration is not easy as the implementations of the systems, their message formats may differ. One way to achieve this is to implement code which bridges these differences (message transformation, rules to integrate, validations etc). However this will be point to point integration. If tomorrow again if there is change in a system the other might also have to be changed which is not good. Instead of this point to point integration which causes tight coupling we can implement an additional layer to mediate the differences between the systems. This results in loose coupling and not affect much our existing systems. 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.

The core functionality of Apache Camel is its routing engine. It allocates messages based on the related routes. A route contains flow and integration logic. It is implemented using EIPs (Enterprise Integration Patterns) and a specific DSL (Domain Specific Language).

Routes in a variety of domain-specific languages (DSL). The most popular ones are: 

The message to be routed in Camel route is present in the Exchange. It is the message holder. Apache camel uses Message Exchange Patterns(MEP). Apache camel exchange can hold any kind of message. It supports a variety of formats like XML, JSON etc.

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.

The CamelContext represents a single Camel routing rulebase. We use the CamelContext in a similar way to the Spring ApplicationContext. public interface CamelContext extends SuspendableService, RuntimeConfiguration. Interface used to represent the context used to configure routes and the policies to use during message exchanges between endpoints.