为何客户端无法连接Spring 5 Java WebSocket服务器？

Hey there, let's figure out why you're hitting that frustrating 404 error when trying to connect to your /event-emitter WebSocket endpoint. Both JavaScript and Java clients throwing the same error tells me the root issue is almost certainly that your Spring server isn't actually mapping that path to a WebSocket handler. Here's how to fix it step by step:

1. Double-Check Your WebSocket Configuration Class #

First, make sure you've properly registered the /event-emitter endpoint in your Spring config. The setup varies depending on whether you're using raw WebSocket or STOMP over WebSocket:

Raw WebSocket Config Example #

If you're using plain WebSocket (no STOMP messaging), your config should look like this:

@Configuration
@EnableWebSocket
public class RawWebSocketConfig implements WebSocketConfigurer {

    @Override
    public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
        // Register your custom handler with the /event-emitter path
        registry.addHandler(new CustomWebSocketHandler(), "/event-emitter")
                .setAllowedOrigins("*"); // Allow cross-origin for dev; restrict in production
    }
}

STOMP Over WebSocket Config Example #

If you're using STOMP (common for messaging apps), your config needs to register the STOMP endpoint explicitly:

@Configuration
@EnableWebSocketMessageBroker
public class StompWebSocketConfig implements WebSocketMessageBrokerConfigurer {

    @Override
    public void registerStompEndpoints(StompEndpointRegistry registry) {
        // Register the /event-emitter endpoint, with optional SockJS fallback
        registry.addEndpoint("/event-emitter")
                .setAllowedOrigins("*")
                .withSockJS(); // Remove this line if you don't need SockJS support
    }

    @Override
    public void configureMessageBroker(MessageBrokerRegistry config) {
        config.enableSimpleBroker("/topic", "/queue"); // Enable in-memory message broker
        config.setApplicationDestinationPrefixes("/app"); // Prefix for app-level message handlers
    }
}

2. Verify the Full Endpoint Path #

If your Spring app has a context path set (e.g., in application.properties as server.servlet.context-path=/my-app), your WebSocket URL must include it. For example:

• Wrong: ws://localhost:8080/event-emitter
• Correct: ws://localhost:8080/my-app/event-emitter

Check your application.properties or application.yml for any context path configuration you might have missed.

3. Match Client Connection Code to Server Setup #

Make sure your client code aligns with whether you're using raw WebSocket or STOMP with SockJS:

JavaScript Client (Raw WebSocket) #

const ws = new WebSocket('ws://localhost:8080/event-emitter');

ws.onopen = () => {
    console.log('Successfully connected to WebSocket!');
};

ws.onerror = (error) => {
    console.error('WebSocket connection error:', error);
};

JavaScript Client (STOMP with SockJS) #

If you enabled withSockJS() in your server config, use the SockJS client library:

// Ensure you've included SockJS and STOMP libraries in your HTML first
const sock = new SockJS('/event-emitter');
const stompClient = Stomp.over(sock);

stompClient.connect({}, (frame) => {
    console.log('Connected to STOMP broker:', frame);
    // Add topic subscriptions here
});

Java Client (Reactor Netty Example) #

For your Java client, confirm the URI includes the correct path (and context path if applicable):

HttpClient client = HttpClient.create();
client.websocket()
      .uri("ws://localhost:8080/event-emitter")
      .handle((inbound, outbound) -> {
          // Handle WebSocket message exchange logic here
          return inbound.receive().then();
      })
      .block();

4. Check Server Startup Logs #

When your Spring app starts, look for logs that confirm the WebSocket endpoint is registered. You should see an entry like this:

Mapped URL path [/event-emitter] onto handler of type [class org.springframework.web.socket.server.support.WebSocketHttpRequestHandler]

If you don't see this log, your config class isn't being picked up by Spring (e.g., it's not in a package scanned by @SpringBootApplication).

Final Notes #

The 404 error is a clear sign the server doesn't recognize /event-emitter as a WebSocket endpoint. Start with verifying your config class, then check path spelling and context path, and ensure client code matches your server setup.

内容的提问来源于stack exchange，提问作者RuF