prakharsrivastav / apache-camel-starter

App with routes, processors and startupcode

Simple app as an apache camel starter

This app shows how to setup a simple camel application with routes and processors. Examples for file and timer based integrations are available. The same application structure can be extended for more complex integrations.

Basics

• Routing rules : A routing rule directs a message from source to target with intermediate processing. a typical syntax for the routing rule is as follows: from("SourceURL").process().to("TergetURL")

Consumers and Producers A local route starts with a consumer (from("SourceURL")) and typically ends with producer (to("TargetURL"))

• Producers: Camel abstractions that refers to an entity capable of sending message to an endpoint
• Consumers: Receives message produced by external system, wrpas them in an exchange and sends them downstream for processing
  • Event Driven Consumers: It is an async receiver that listens on a channel eg tcp/ip port, jms queue websocket etc.
  • Polling Consumers: sync receiver that actively goes and fetches messages from a particular source like ftp,

Exchange message The exchange object consists of the message that is propagated through the route. The main constituents of the exchange message are as follows:

• In Message: The current message being processed by Camel. It consists of following components

  • Body
  • Headers
  • Attachments

• Out Message:

  • Certain process nodes can treat In message as request and process/transform them.
  • This transformed message is then set as the Out message.
  • The old In message is discarded and the Out message is moved to the In message slot.

• Message Exchange Patterns (MEP) effects the interaction between the exchanges and the endpoints.

  • Consumer Endpoint sets the initial value of the MEP. The initial value determines if the consumer enpoint expects a reply (InOut MEP) or not (InOnly MEP).
  • Producer Endpoint . The MEP affects the producer endpoints. For eg , if the current MEP is InOnly, then producer does not expect to recieve a reply from the endpoint.

• Exchange properties a list of named properties containing metadata for the current message.

Message Exchange Patterns

• InOnly
• RobustInOnly
• InOut
• InOptinalOut
• OutOnly
• RobustOutOnly
• OutIn
• OutOptionalIn

** Processors ** ** Expressions and predicates **

Directory Structure

• Application.java : Bootstrap application , add routes and lifecycle events. Services like tracing and logging drivers can be injected here
• processors/ : Package to hold all message processors.
• routes: Package to hold route builders
• models: Package to hold any models/domain objects