Handling ‘state’ in Java WebSocket applications

By and large, there are two kinds of states in a WebSocket application

• User/client specific: related to a connected user/Session e.g. user ID, list of subscriptions, last message received etc.
• Global: state which is relevant across your application and something which all connected users/Sessions might be able to use

User specific state

This can be handled using getUserProperties method on the Session object – this exposes a Map which you can use to store anything (Object type) using a String type key

Global state

There are multiple options here as well. Please note that these are scoped to a specific Endpoint

• getUserProperties in EndpointConfig – it exposes the same Map interface as the one in Session. Since the WebSocket runtime creates a single instance of an EndpointConfig object per Endpoint , it can be used a global state store

• Another option is to encapsulate some of the common/global logic in a custom Configurator implementation which can be accessed & used within the endpoint logic

Further reading

• Java WebSocket API specification
• Java WebSocket API Handbook
• Other WebSocket blogs

Cheers!