Spring WebSocket

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-websocket</artifactId>
    <version>7.0.1</version>
</dependency>

implementation 'org.springframework:spring-websocket:7.0.1'

// Core WebSocket API
import org.springframework.web.socket.WebSocketHandler;
import org.springframework.web.socket.WebSocketSession;
import org.springframework.web.socket.TextMessage;
import org.springframework.web.socket.BinaryMessage;
import org.springframework.web.socket.CloseStatus;

// Handler base classes
import org.springframework.web.socket.handler.TextWebSocketHandler;
import org.springframework.web.socket.handler.BinaryWebSocketHandler;

// Configuration
import org.springframework.web.socket.config.annotation.EnableWebSocket;
import org.springframework.web.socket.config.annotation.EnableWebSocketMessageBroker;
import org.springframework.web.socket.config.annotation.WebSocketConfigurer;
import org.springframework.web.socket.config.annotation.WebSocketHandlerRegistry;

// STOMP messaging
import org.springframework.messaging.handler.annotation.MessageMapping;
import org.springframework.messaging.handler.annotation.SendTo;

public class MyHandler extends TextWebSocketHandler {
    @Override
    protected void handleTextMessage(WebSocketSession session, TextMessage message)
            throws Exception {
        session.sendMessage(new TextMessage("Echo: " + message.getPayload()));
    }
}

@Configuration
@EnableWebSocket
public class WebSocketConfig implements WebSocketConfigurer {
    @Override
    public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
        registry.addHandler(new MyHandler(), "/ws")
                .setAllowedOrigins("*");
    }
}

@Configuration
@EnableWebSocketMessageBroker
public class StompConfig implements WebSocketMessageBrokerConfigurer {
    @Override
    public void registerStompEndpoints(StompEndpointRegistry registry) {
        registry.addEndpoint("/stomp").withSockJS();
    }

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

@Controller
public class MessageController {
    @MessageMapping("/chat")
    @SendTo("/topic/messages")
    public String handleMessage(String message) {
        return "Received: " + message;
    }
}

public interface WebSocketHandler {
    void afterConnectionEstablished(WebSocketSession session) throws Exception;
    void handleMessage(WebSocketSession session, WebSocketMessage<?> message) throws Exception;
    void handleTransportError(WebSocketSession session, Throwable exception) throws Exception;
    void afterConnectionClosed(WebSocketSession session, CloseStatus closeStatus) throws Exception;
    boolean supportsPartialMessages();
}

public interface WebSocketSession {
    String getId();
    URI getUri();
    HttpHeaders getHandshakeHeaders();
    Map<String, Object> getAttributes();
    Principal getPrincipal();
    void sendMessage(WebSocketMessage<?> message) throws IOException;
    boolean isOpen();
    void close(CloseStatus status) throws IOException;
}

// Text message
new TextMessage(CharSequence payload);
new TextMessage(CharSequence payload, boolean isLast); // For partial messages

// Binary message
new BinaryMessage(ByteBuffer payload);
new BinaryMessage(byte[] payload);

// Control messages
new PingMessage();
new PongMessage();

CloseStatus.NORMAL                  // 1000
CloseStatus.GOING_AWAY              // 1001
CloseStatus.PROTOCOL_ERROR          // 1002
CloseStatus.NOT_ACCEPTABLE          // 1003
CloseStatus.BAD_DATA                // 1007
CloseStatus.POLICY_VIOLATION        // 1008
CloseStatus.TOO_BIG_TO_PROCESS      // 1009
CloseStatus.SERVER_ERROR            // 1011