Fix code smell in websocket and webflux modules (#2669)

* * Fix code smell in websocket and webflux modules

* * More fixes

* * Fix NPE in the `IntegrationHandlerResultHandler`

spring-integration-core/src/main/java/org/springframework/integration/transformer/PayloadTypeConvertingTransformer.java

@@ -53,7 +53,7 @@ public class PayloadTypeConvertingTransformer<T, U> extends AbstractPayloadTrans
 	}
 
 	@Override
-	protected void onInit() throws Exception {
+	protected void onInit() throws Exception { // NOSONAR thrown by super class
 		super.onInit();
 		Assert.notNull(this.converter, () -> getClass().getName() + " requires a Converter<Object, Object>");
 	}

spring-integration-scripting/src/main/java/org/springframework/integration/scripting/dsl/DslScriptExecutingMessageProcessor.java

@@ -105,7 +105,7 @@ class DslScriptExecutingMessageProcessor
 			String filename = this.script.getFilename();
 			int index =
 					filename != null
-							? filename.lastIndexOf(".") + 1
+							? filename.lastIndexOf('.') + 1
 							: -1;
 			if (index < 1) {
 				throw new BeanCreationException(

spring-integration-webflux/src/main/java/org/springframework/integration/webflux/inbound/IntegrationHandlerResultHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2017 the original author or authors.
+ * Copyright 2017-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -47,7 +47,8 @@ public class IntegrationHandlerResultHandler implements HandlerResultHandler, Or
 	@Override
 	@SuppressWarnings("unchecked")
 	public Mono<Void> handleResult(ServerWebExchange exchange, HandlerResult result) {
-		return (Mono<Void>) result.getReturnValue();
+		Object returnValue = result.getReturnValue();
+		return returnValue == null ? Mono.empty() : (Mono<Void>) returnValue;
 	}
 
 	@Override

spring-integration-webflux/src/main/java/org/springframework/integration/webflux/inbound/WebFluxInboundEndpoint.java

@@ -80,6 +80,8 @@ public class WebFluxInboundEndpoint extends BaseHttpInboundEndpoint implements W
 
 	private static final MediaType MEDIA_TYPE_APPLICATION_ALL = new MediaType("application");
 
+	private static final String UNCHECKED = "unchecked";
+
 	private static final List<HttpMethod> SAFE_METHODS = Arrays.asList(HttpMethod.GET, HttpMethod.HEAD);
 
 	private ServerCodecConfigurer codecConfigurer = ServerCodecConfigurer.create();
@@ -130,11 +132,6 @@ public class WebFluxInboundEndpoint extends BaseHttpInboundEndpoint implements W
 		return super.getComponentType().replaceFirst("http", "webflux");
 	}
 
-	@Override
-	protected void onInit() throws Exception {
-		super.onInit();
-	}
-
 	@Override
 	public Mono<Void> handle(ServerWebExchange exchange) {
 		return Mono.defer(() -> {
@@ -147,7 +144,6 @@ public class WebFluxInboundEndpoint extends BaseHttpInboundEndpoint implements W
 		});
 	}
 
-	@SuppressWarnings("unchecked")
 	private Mono<Void> doHandle(ServerWebExchange exchange) {
 		return extractRequestBody(exchange)
 				.doOnSubscribe(s -> this.activeCount.incrementAndGet())
@@ -170,7 +166,7 @@ public class WebFluxInboundEndpoint extends BaseHttpInboundEndpoint implements W
 
 	}
 
-	@SuppressWarnings("unchecked")
+	@SuppressWarnings(UNCHECKED)
 	private <T> Mono<T> extractRequestBody(ServerWebExchange exchange) {
 		ServerHttpRequest request = exchange.getRequest();
 		ServerHttpResponse response = exchange.getResponse();
@@ -201,7 +197,8 @@ public class WebFluxInboundEndpoint extends BaseHttpInboundEndpoint implements W
 
 				Class<?> resolvedType = bodyType.resolve();
 
-				ReactiveAdapter adapter = (resolvedType != null ? this.adapterRegistry.getAdapter(resolvedType) : null);
+				ReactiveAdapter adapter = (resolvedType != null ? this.adapterRegistry.getAdapter(resolvedType) :
+						null);
 				ResolvableType elementType = (adapter != null ? bodyType.getGeneric() : bodyType);
 
 				HttpMessageReader<?> httpMessageReader = this.codecConfigurer
@@ -237,40 +234,14 @@ public class WebFluxInboundEndpoint extends BaseHttpInboundEndpoint implements W
 		}
 	}
 
-	@SuppressWarnings("unchecked")
+	@SuppressWarnings(UNCHECKED)
 	private Mono<Tuple2<Message<Object>, RequestEntity<?>>> buildMessage(RequestEntity<?> httpEntity,
 			ServerWebExchange exchange) {
 
 		ServerHttpRequest request = exchange.getRequest();
-		HttpHeaders requestHeaders = request.getHeaders();
-		Map<String, Object> exchangeAttributes = exchange.getAttributes();
-
-		StandardEvaluationContext evaluationContext = createEvaluationContext();
-
-		evaluationContext.setVariable("requestAttributes", exchangeAttributes);
 		MultiValueMap<String, String> requestParams = request.getQueryParams();
-		evaluationContext.setVariable("requestParams", requestParams);
-		evaluationContext.setVariable("requestHeaders", requestHeaders);
-		if (!CollectionUtils.isEmpty(request.getCookies())) {
-			evaluationContext.setVariable("cookies", request.getCookies());
-		}
 
-		Map<String, String> pathVariables =
-				(Map<String, String>) exchangeAttributes.get(HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE);
-
-		if (!CollectionUtils.isEmpty(pathVariables)) {
-			evaluationContext.setVariable("pathVariables", pathVariables);
-		}
-
-		Map<String, MultiValueMap<String, String>> matrixVariables =
-				(Map<String, MultiValueMap<String, String>>) exchangeAttributes
-						.get(HandlerMapping.MATRIX_VARIABLES_ATTRIBUTE);
-
-		if (!CollectionUtils.isEmpty(matrixVariables)) {
-			evaluationContext.setVariable("matrixVariables", matrixVariables);
-		}
-
-		evaluationContext.setRootObject(httpEntity);
+		StandardEvaluationContext evaluationContext = buildEvaluationContext(httpEntity, exchange);
 		Object payload;
 		if (getPayloadExpression() != null) {
 			payload = getPayloadExpression().getValue(evaluationContext);
@@ -310,10 +281,13 @@ public class WebFluxInboundEndpoint extends BaseHttpInboundEndpoint implements W
 							.copyHeaders(headers);
 		}
 
-		messageBuilder
-				.setHeader(org.springframework.integration.http.HttpHeaders.REQUEST_URL, request.getURI().toString())
-				.setHeader(org.springframework.integration.http.HttpHeaders.REQUEST_METHOD,
-						request.getMethod().toString());
+		messageBuilder.setHeader(org.springframework.integration.http.HttpHeaders.REQUEST_URL,
+				request.getURI().toString());
+		HttpMethod httpMethod = request.getMethod();
+		if (httpMethod != null) {
+			messageBuilder.setHeader(org.springframework.integration.http.HttpHeaders.REQUEST_METHOD,
+					httpMethod.toString());
+		}
 
 		return exchange.getPrincipal()
 				.map(principal ->
@@ -324,6 +298,41 @@ public class WebFluxInboundEndpoint extends BaseHttpInboundEndpoint implements W
 				.zipWith(Mono.just(httpEntity));
 	}
 
+	@SuppressWarnings(UNCHECKED)
+	private StandardEvaluationContext buildEvaluationContext(RequestEntity<?> httpEntity, ServerWebExchange exchange) {
+		ServerHttpRequest request = exchange.getRequest();
+		HttpHeaders requestHeaders = request.getHeaders();
+		MultiValueMap<String, String> requestParams = request.getQueryParams();
+		Map<String, Object> exchangeAttributes = exchange.getAttributes();
+
+		StandardEvaluationContext evaluationContext = createEvaluationContext();
+
+		evaluationContext.setVariable("requestAttributes", exchangeAttributes);
+		evaluationContext.setVariable("requestParams", requestParams);
+		evaluationContext.setVariable("requestHeaders", requestHeaders);
+		if (!CollectionUtils.isEmpty(request.getCookies())) {
+			evaluationContext.setVariable("cookies", request.getCookies());
+		}
+
+		Map<String, String> pathVariables =
+				(Map<String, String>) exchangeAttributes.get(HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE);
+
+		if (!CollectionUtils.isEmpty(pathVariables)) {
+			evaluationContext.setVariable("pathVariables", pathVariables);
+		}
+
+		Map<String, MultiValueMap<String, String>> matrixVariables =
+				(Map<String, MultiValueMap<String, String>>) exchangeAttributes
+						.get(HandlerMapping.MATRIX_VARIABLES_ATTRIBUTE);
+
+		if (!CollectionUtils.isEmpty(matrixVariables)) {
+			evaluationContext.setVariable("matrixVariables", matrixVariables);
+		}
+
+		evaluationContext.setRootObject(httpEntity);
+		return evaluationContext;
+	}
+
 	private Mono<Void> populateResponse(ServerWebExchange exchange, Message<?> replyMessage) {
 		ServerHttpResponse response = exchange.getResponse();
 		getHeaderMapper().fromHeaders(replyMessage.getHeaders(), response.getHeaders());
@@ -379,7 +388,7 @@ public class WebFluxInboundEndpoint extends BaseHttpInboundEndpoint implements W
 		}
 	}
 
-	@SuppressWarnings("unchecked")
+	@SuppressWarnings(UNCHECKED)
 	private Mono<Void> writeResponseBody(ServerWebExchange exchange, Object body) {
 		ResolvableType bodyType = ResolvableType.forInstance(body);
 		ReactiveAdapter adapter = this.adapterRegistry.getAdapter(bodyType.resolve(), body);
@@ -473,7 +482,7 @@ public class WebFluxInboundEndpoint extends BaseHttpInboundEndpoint implements W
 		return (mediaTypes.isEmpty() ? Collections.singletonList(MediaType.ALL) : mediaTypes);
 	}
 
-	@SuppressWarnings("unchecked")
+	@SuppressWarnings(UNCHECKED)
 	private List<MediaType> getProducibleTypes(ServerWebExchange exchange,
 			Supplier<List<MediaType>> producibleTypesSupplier) {
 
@@ -482,9 +491,9 @@ public class WebFluxInboundEndpoint extends BaseHttpInboundEndpoint implements W
 	}
 
 	private MediaType selectMoreSpecificMediaType(MediaType acceptable, MediaType producible) {
-		producible = producible.copyQualityValue(acceptable);
+		MediaType producibleToUse = producible.copyQualityValue(acceptable);
 		Comparator<MediaType> comparator = MediaType.SPECIFICITY_COMPARATOR;
-		return (comparator.compare(acceptable, producible) <= 0 ? acceptable : producible);
+		return (comparator.compare(acceptable, producibleToUse) <= 0 ? acceptable : producibleToUse);
 	}
 
 

spring-integration-webflux/src/main/java/org/springframework/integration/webflux/inbound/WebFluxIntegrationRequestMappingHandlerMapping.java

@@ -119,11 +119,11 @@ public class WebFluxIntegrationRequestMappingHandlerMapping extends RequestMappi
 	@Override
 	protected void detectHandlerMethods(Object handler) {
 		if (handler instanceof String) {
-			handler = getApplicationContext().getBean((String) handler);
+			handler = getApplicationContext().getBean((String) handler); // NOSONAR never null
 		}
 		RequestMappingInfo mapping = getMappingForEndpoint((WebFluxInboundEndpoint) handler);
 		if (mapping != null) {
-			registerMapping(mapping, handler, HANDLER_METHOD);
+			registerMapping(mapping, handler, HANDLER_METHOD); // NOSONAR never null
 		}
 	}
 

spring-integration-webflux/src/main/java/org/springframework/integration/webflux/outbound/WebFluxRequestExecutingMessageHandler.java

@@ -159,7 +159,7 @@ public class WebFluxRequestExecutingMessageHandler extends AbstractHttpRequestEx
 						.headers(headers -> headers.putAll(httpRequest.getHeaders()));
 
 		if (httpRequest.hasBody()) {
-			requestSpec.body(BodyInserters.fromObject(httpRequest.getBody()));
+			requestSpec.body(BodyInserters.fromObject(httpRequest.getBody())); // NOSONAR protected with hasBody()
 		}
 
 		Mono<ClientResponse> responseMono =

spring-integration-websocket/src/main/java/org/springframework/integration/websocket/config/WebSocketIntegrationConfigurationInitializer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2017 the original author or authors.
+ * Copyright 2014-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,12 +16,11 @@
 
 package org.springframework.integration.websocket.config;
 
-import java.util.Collection;
-
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 
 import org.springframework.beans.BeansException;
+import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.ListableBeanFactory;
 import org.springframework.beans.factory.config.AbstractFactoryBean;
 import org.springframework.beans.factory.config.BeanDefinition;
@@ -50,10 +49,12 @@ import org.springframework.web.socket.config.annotation.WebSocketConfigurer;
  */
 public class WebSocketIntegrationConfigurationInitializer implements IntegrationConfigurationInitializer {
 
-	private static final Log logger = LogFactory.getLog(WebSocketIntegrationConfigurationInitializer.class);
+	private static final Log logger = // NOSONAR lower case
+			LogFactory.getLog(WebSocketIntegrationConfigurationInitializer.class);
 
-	private static final boolean servletPresent = ClassUtils.isPresent("javax.servlet.Servlet",
-			WebSocketIntegrationConfigurationInitializer.class.getClassLoader());
+	private static final boolean servletPresent = // NOSONAR lower case
+			ClassUtils.isPresent("javax.servlet.Servlet",
+					WebSocketIntegrationConfigurationInitializer.class.getClassLoader());
 
 	private static final String WEB_SOCKET_HANDLER_MAPPING_BEAN_NAME = "integrationWebSocketHandlerMapping";
 
@@ -130,11 +131,13 @@ public class WebSocketIntegrationConfigurationInitializer implements Integration
 		}
 
 		@Override
-		protected HandlerMapping createInstance() throws Exception {
-			Collection<WebSocketConfigurer> webSocketConfigurers =
-					((ListableBeanFactory) getBeanFactory()).getBeansOfType(WebSocketConfigurer.class).values();
-			for (WebSocketConfigurer configurer : webSocketConfigurers) {
-				configurer.registerWebSocketHandlers(this.registry);
+		protected HandlerMapping createInstance() {
+			BeanFactory beanFactory = getBeanFactory();
+			if (beanFactory != null) {
+				((ListableBeanFactory) beanFactory)
+						.getBeansOfType(WebSocketConfigurer.class)
+						.values()
+						.forEach(configurer -> configurer.registerWebSocketHandlers(this.registry));
 			}
 			if (this.registry.requiresTaskScheduler()) {
 				this.registry.setTaskScheduler(this.sockJsTaskScheduler);

spring-integration-websocket/src/main/java/org/springframework/integration/websocket/inbound/WebSocketInboundChannelAdapter.java

@@ -220,7 +220,7 @@ public class WebSocketInboundChannelAdapter extends MessageProducerSupport
 	}
 
 	@Override
-	public void afterSessionStarted(WebSocketSession session) throws Exception {
+	public void afterSessionStarted(WebSocketSession session) throws Exception { // NOSONAR Thrown from the delegate
 		if (isActive()) {
 			SubProtocolHandler protocolHandler = this.subProtocolHandlerRegistry.findProtocolHandler(session);
 			protocolHandler.afterSessionStarted(session, this.subProtocolHandlerChannel);
@@ -237,7 +237,8 @@ public class WebSocketInboundChannelAdapter extends MessageProducerSupport
 	}
 
 	@Override
-	public void afterSessionEnded(WebSocketSession session, CloseStatus closeStatus) throws Exception {
+	public void afterSessionEnded(WebSocketSession session, CloseStatus closeStatus)
+			throws Exception { // NOSONAR Thrown from the delegate
 		if (isActive()) {
 			this.subProtocolHandlerRegistry.findProtocolHandler(session)
 					.afterSessionEnded(session, closeStatus, this.subProtocolHandlerChannel);
@@ -245,7 +246,8 @@ public class WebSocketInboundChannelAdapter extends MessageProducerSupport
 	}
 
 	@Override
-	public void onMessage(WebSocketSession session, WebSocketMessage<?> webSocketMessage) throws Exception {
+	public void onMessage(WebSocketSession session, WebSocketMessage<?> webSocketMessage)
+			throws Exception { // NOSONAR Thrown from the delegate
 		if (isActive()) {
 			this.subProtocolHandlerRegistry.findProtocolHandler(session)
 					.handleMessageFromClient(session, webSocketMessage, this.subProtocolHandlerChannel);
@@ -281,23 +283,13 @@ public class WebSocketInboundChannelAdapter extends MessageProducerSupport
 	}
 
 	@SuppressWarnings("unchecked")
-	private void handleMessageAndSend(Message<?> message) throws Exception {
+	private void handleMessageAndSend(final Message<?> message) {
 		SimpMessageHeaderAccessor headerAccessor = SimpMessageHeaderAccessor.wrap(message);
 		StompCommand stompCommand = (StompCommand) headerAccessor.getHeader("stompCommand");
 		SimpMessageType messageType = headerAccessor.getMessageType();
-		if ((messageType == null || SimpMessageType.MESSAGE.equals(messageType)
-				|| (SimpMessageType.CONNECT.equals(messageType) && !this.useBroker)
-				|| StompCommand.CONNECTED.equals(stompCommand)
-				|| StompCommand.RECEIPT.equals(stompCommand))
-				&& !checkDestinationPrefix(headerAccessor.getDestination())) {
+		if (isProcessingTypeOrCommand(headerAccessor, stompCommand, messageType)) {
 			if (SimpMessageType.CONNECT.equals(messageType)) {
-				String sessionId = headerAccessor.getSessionId();
-				SimpMessageHeaderAccessor connectAck = SimpMessageHeaderAccessor.create(SimpMessageType.CONNECT_ACK);
-				connectAck.setSessionId(sessionId);
-				connectAck.setHeader(SimpMessageHeaderAccessor.CONNECT_MESSAGE_HEADER, message);
-				Message<byte[]> ackMessage = MessageBuilder.createMessage(EMPTY_PAYLOAD, connectAck.getMessageHeaders());
-				WebSocketSession session = this.webSocketContainer.getSession(sessionId);
-				this.subProtocolHandlerRegistry.findProtocolHandler(session).handleMessageToClient(session, ackMessage);
+				produceConnectAckMessage(message, headerAccessor);
 			}
 			else if (StompCommand.CONNECTED.equals(stompCommand)) {
 				this.eventPublisher.publishEvent(new SessionConnectedEvent(this, (Message<byte[]>) message));
@@ -306,9 +298,7 @@ public class WebSocketInboundChannelAdapter extends MessageProducerSupport
 				this.eventPublisher.publishEvent(new ReceiptEvent(this, (Message<byte[]>) message));
 			}
 			else {
-				headerAccessor.removeHeader(SimpMessageHeaderAccessor.NATIVE_HEADERS);
-				Object payload = this.messageConverter.fromMessage(message, this.payloadType.get());
-				sendMessage(getMessageBuilderFactory().withPayload(payload).copyHeaders(headerAccessor.toMap()).build());
+				produceMessage(message, headerAccessor);
 			}
 		}
 		else {
@@ -324,19 +314,56 @@ public class WebSocketInboundChannelAdapter extends MessageProducerSupport
 		}
 	}
 
+	private boolean isProcessingTypeOrCommand(SimpMessageHeaderAccessor headerAccessor, StompCommand stompCommand,
+			SimpMessageType messageType) {
+
+		return (messageType == null // NOSONAR pretty simple logic
+				|| SimpMessageType.MESSAGE.equals(messageType)
+				|| (SimpMessageType.CONNECT.equals(messageType) && !this.useBroker)
+				|| StompCommand.CONNECTED.equals(stompCommand)
+				|| StompCommand.RECEIPT.equals(stompCommand))
+				&& !checkDestinationPrefix(headerAccessor.getDestination());
+	}
+
 	private boolean checkDestinationPrefix(String destination) {
 		if (this.useBroker) {
 			Collection<String> destinationPrefixes = this.brokerHandler.getDestinationPrefixes();
 			if ((destination == null) || CollectionUtils.isEmpty(destinationPrefixes)) {
 				return false;
 			}
-			for (String prefix : destinationPrefixes) {
-				if (destination.startsWith(prefix)) {
-					return true;
-				}
-			}
+			return destinationPrefixes.stream().anyMatch(destination::startsWith);
 		}
 		return false;
 	}
 
+	private void produceConnectAckMessage(Message<?> message, SimpMessageHeaderAccessor headerAccessor) {
+		String sessionId = headerAccessor.getSessionId();
+		SimpMessageHeaderAccessor connectAck = SimpMessageHeaderAccessor.create(SimpMessageType.CONNECT_ACK);
+		connectAck.setSessionId(sessionId);
+		connectAck.setHeader(SimpMessageHeaderAccessor.CONNECT_MESSAGE_HEADER, message);
+		Message<byte[]> ackMessage = MessageBuilder.createMessage(EMPTY_PAYLOAD, connectAck.getMessageHeaders());
+		WebSocketSession session = this.webSocketContainer.getSession(sessionId);
+		try {
+			this.subProtocolHandlerRegistry.findProtocolHandler(session).handleMessageToClient(session, ackMessage);
+		}
+		catch (Exception e) {
+			throw new MessageHandlingException(message, "Error sending connect ack message", e);
+		}
+	}
+
+	private void produceMessage(Message<?> message, SimpMessageHeaderAccessor headerAccessor) {
+		headerAccessor.removeHeader(SimpMessageHeaderAccessor.NATIVE_HEADERS);
+		Object payload = this.messageConverter.fromMessage(message, this.payloadType.get());
+		Assert.state(payload != null,
+				() -> "The message converter '" + this.messageConverter +
+						"' produced no payload for message '" + message +
+						"' and expected payload type: " + this.payloadType.get());
+		Message<Object> messageToSend =
+				getMessageBuilderFactory()
+						.withPayload(payload)
+						.copyHeaders(headerAccessor.toMap())
+						.build();
+		sendMessage(messageToSend);
+	}
+
 }

spring-integration-websocket/src/main/java/org/springframework/integration/websocket/outbound/WebSocketOutboundMessageHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2017 the original author or authors.
+ * Copyright 2014-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -43,11 +43,12 @@ import org.springframework.web.socket.handler.SessionLimitExceededException;
 
 /**
  * @author Artem Bilan
+ *
  * @since 4.1
  */
 public class WebSocketOutboundMessageHandler extends AbstractMessageHandler {
 
-	private final List<MessageConverter> defaultConverters = new ArrayList<MessageConverter>(3);
+	private final List<MessageConverter> defaultConverters = new ArrayList<>(3);
 
 	{
 		this.defaultConverters.add(new StringMessageConverter());
@@ -79,13 +80,14 @@ public class WebSocketOutboundMessageHandler extends AbstractMessageHandler {
 
 	public WebSocketOutboundMessageHandler(IntegrationWebSocketContainer webSocketContainer,
 			SubProtocolHandlerRegistry protocolHandlerRegistry) {
+
 		Assert.notNull(webSocketContainer, "'webSocketContainer' must not be null");
 		Assert.notNull(protocolHandlerRegistry, "'protocolHandlerRegistry' must not be null");
 		this.webSocketContainer = webSocketContainer;
 		this.client = webSocketContainer instanceof ClientWebSocketContainer;
 		this.subProtocolHandlerRegistry = protocolHandlerRegistry;
 		List<String> subProtocols = protocolHandlerRegistry.getSubProtocols();
-		this.webSocketContainer.addSupportedProtocols(subProtocols.toArray(new String[subProtocols.size()]));
+		this.webSocketContainer.addSupportedProtocols(subProtocols.toArray(new String[0]));
 	}
 
 	/**
@@ -95,7 +97,7 @@ public class WebSocketOutboundMessageHandler extends AbstractMessageHandler {
 	 */
 	public void setMessageConverters(List<MessageConverter> messageConverters) {
 		Assert.noNullElements(messageConverters.toArray(), "'messageConverters' must not contain null entries");
-		this.messageConverters = new ArrayList<MessageConverter>(messageConverters);
+		this.messageConverters = new ArrayList<>(messageConverters);
 	}
 
 
@@ -147,7 +149,12 @@ public class WebSocketOutboundMessageHandler extends AbstractMessageHandler {
 			SimpMessageHeaderAccessor headers = SimpMessageHeaderAccessor.wrap(message);
 			headers.setLeaveMutable(true);
 			headers.setMessageTypeIfNotSet(SimpMessageType.MESSAGE);
-			Message<?> messageToSend = this.messageConverter.toMessage(message.getPayload(), headers.getMessageHeaders());
+			Object payload = message.getPayload();
+			Message<?> messageToSend =
+					this.messageConverter.toMessage(payload, headers.getMessageHeaders());
+			Assert.state(messageToSend != null,
+					() -> "The message converter '" + this.messageConverter +
+							"' produced no message to send based on the request message: '" + message + "'");
 			this.subProtocolHandlerRegistry.findProtocolHandler(session).handleMessageToClient(session, messageToSend);
 		}
 		catch (SessionLimitExceededException ex) {