Spring with WebSocket

消息架構

Today REST is a widely accepted, understood, and supported architecture for building web applications. It is an architecture that relies on having many URLs (nouns), a handful of HTTP methods (verbs), and other principles such as using hypermedia (links), remaining stateless, etc.

REST的架構是經過不少URL去實現的

By contrast a WebSocket application may use a single URL only for the initial HTTP handshake. All messages thereafter share and flow on the same TCP connection. This points to an entirely different, asynchronous, event-driven, messaging architecture. One that is much closer to traditional messaging applications (e.g. JMS, AMQP).

WebSocket的握手卻只須要一次HTTP請求

子協議

須要上層的子協議去解析進來的消息

This is comparable to how most web applications today are written using a web framework rather than the Servlet API alone.

STOMP （Spring支持）

Spring裏頭關於WebSocket幾個重要的概念

WebSocketHandler

定義進來的消息怎麼處理

WebSocketConfigurer

Provides methods for configuring WebSocketHandler request mappings.

這個接口只有一個方法：

addHandler(WebSocketHandler webSocketHandler, java.lang.String... paths)

Configure a WebSocketHandler at the specified URL paths.

創建鏈接

要在服務器端準備好WebSocket Engine

根據具體的服務器不同辦法也不同，由於WebSocket是http的Upgrade協議，因此須要UpgradeStrategy也不難理解

@Configuration
@EnableWebSocket
public class WebSocketConfig implements WebSocketConfigurer {

    @Override
    public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
        registry.addHandler(echoWebSocketHandler(),
            "/echo").setHandshakeHandler(handshakeHandler()).withSocketJS();
    }

    @Bean
    public DefaultHandshakeHandler handshakeHandler() {

        WebSocketPolicy policy = new WebSocketPolicy(WebSocketBehavior.SERVER);
        policy.setInputBufferSize(8192);
        policy.setIdleTimeout(600000);

        return new DefaultHandshakeHandler(
                new JettyRequestUpgradeStrategy(new WebSocketServerFactory(policy)));
    }

}

WebSocketMessageBrokerConfigurer

它竟然不是WebSocketConfigurer的子類。。。

兩個方法： configureMessageBroker 服務器開放的端口讓客戶端監聽，也就是說寫的時候往這裏寫

@Override
    public void configureMessageBroker(MessageBrokerRegistry config) {
        config.setApplicationDestinationPrefixes("/app");
        config.enableSimpleBroker("/queue", "/topic");
    }

registerStompEndpoints 服務器要監聽的端口，message會從這裏進來，要對這裏加一個Handler

@Override
	public void registerStompEndpoints(StompEndpointRegistry registry) {
		registry.addEndpoint("/hello").withSockJS();
	}