Message Processor Application

This is a simple Play Framework application that receives JSON messages, puts them on a Redis pub/sub channel, persists them to Redis and sends out the received messages to connected clients over Websockets.

Usage

By default, the application is configured to listen on port 9000.

Messages can be sent by POSTing a JSON request with the appropriate application/json content type header to http://example.com:9000/messages.

The messages currently saved in the system can be retrieved as a JSON array by sending a GET request to http://example.com:9000/messages.

The web UI for monitoring incoming messages can be accessed by visiting http://example.com:9000 using a modern browser that supports Websockets. The page is initially empty, but it will show JSON messages as they start coming in.

Implementation

Controllers

Consistent with the framework's conventions, the controllers are implemented in the app/controllers package.

Web UI

The Application controller serves the simple HTML page for monitoring the incoming messages, and also provides the Websocket connection required for real-time communication from the server to the client browser.

REST service

The REST service endpoints are implemented in the Messages controller.

POST /messages expects an application/json message in the request body. Returns 201 Created if the request was successfully processed, 400 Bad Request if the request was not valid JSON.

GET /messages returns the messages currently persisted in the system as a JSON array.

Application logic

The main application logic is implemented in the app/models package.

Actors

There are three actors in the application:

• WebSocketSender receives JsonNode messages and writes them to the underlying Websocket connection.
• WebSocketSenderSupervisor manages the connected Websocket clients by handling Add and Remove messages and delegating JsonNode messages to all currently active WebSocketSender actors.
• RedisPublisher publishes JsonNode messages on its underlying Redis pub/sub channel.

Message repository

Messages are persisted and retrieved using the MessageRepository class. The keys of newly persisted messages are saved to a set in Redis, which in turn is used for retrieving all persisted messages. This method is preferred to simply using the KEYS command in application code.

Redis pub/sub listener

The MessagePubSub listener is registered in the Global class at application startup and is removed when the application is shut down.