UndertowConfig.java

import io.undertow.connector.ByteBufferPool;
import io.undertow.server.DefaultByteBufferPool;
import io.undertow.websockets.jsr.WebSocketDeploymentInfo;
import org.springframework.boot.web.embedded.undertow.UndertowServletWebServerFactory;
import org.springframework.boot.web.server.WebServerFactoryCustomizer;
import org.springframework.context.annotation.Configuration;

@Configuration
class UndertowConfig implements WebServerFactoryCustomizer<UndertowServletWebServerFactory> {

    private static final int POOL_BUFFER_SIZE = 16384;

    private static final boolean POOL_USE_DIRECT_BUFFERS = true;

    @Override
    public void customize(UndertowServletWebServerFactory factory) {
        factory.addDeploymentInfoCustomizers(deploymentInfo -> {
            deploymentInfo.addServletContextAttribute(WebSocketDeploymentInfo.ATTRIBUTE_NAME, createWebSocketDeploymentInfo());
        });
    }

    private WebSocketDeploymentInfo createWebSocketDeploymentInfo() {
        ByteBufferPool byteBufferPool = new DefaultByteBufferPool(POOL_USE_DIRECT_BUFFERS, POOL_BUFFER_SIZE);
        WebSocketDeploymentInfo webSocketDeploymentInfo = new WebSocketDeploymentInfo();
        webSocketDeploymentInfo.setBuffers(byteBufferPool);
        webSocketDeploymentInfo.setDispatchToWorkerThread(true);
        return webSocketDeploymentInfo;
    }
}