WebSocket messaging that includes raw WebSocket interactions, WebSocket emulation through SockJS, and publish-subscribe messaging through STOMP as a sub-protocol over WebSocket.
4.1. Introduction to WebSocket
4.2. WebSocket API
The Spring Framework provides a WebSocket API that you can use to write client- and server-side applications that handle WebSocket messages.
4.3. SockJS Fallback
Over the public Internet, restrictive proxies outside your control may preclude WebSocket interactions, either because they are not configured to pass on the Upgrade header or because they close long-lived connections that appear to be idle.
The solution to this problem is WebSocket emulation — that is, attempting to use WebSocket first and then falling back on HTTP-based techniques that emulate a WebSocket interaction and expose the same application-level API.
On the Servlet stack, the Spring Framework provides both server (and also client) support for the SockJS protocol.
4.3.1. Overview
The goal of SockJS is to let applications use a WebSocket API but fall back to non-WebSocket alternatives when necessary at runtime, without the need to change application code.
4.4. STOMP
The WebSocket protocol defines two types of messages (text and binary), but their content is undefined. The protocol defines a mechanism for client and server to negotiate a sub-protocol (that is, a higher-level messaging protocol) to use on top of WebSocket to define what kind of messages each can send, what the format is, the content of each message, and so on. The use of a sub-protocol is optional but, either way, the client and the server need to agree on some protocol that defines message content.
4.4.1. Overview
STOMP (Simple Text Oriented Messaging Protocol) was originally created for scripting languages to connect to enterprise message brokers. It is designed to address a minimal subset of commonly used messaging patterns. STOMP can be used over any reliable two-way streaming network protocol, such as TCP and WebSocket. Although STOMP is a text-oriented protocol, message payloads can be either text or binary.
4.4.2. Benefits
Using STOMP as a sub-protocol lets the Spring Framework and Spring Security provide a richer programming model versus using raw WebSockets.