Apply Nullability to spring-integration-websocket module

Related to: spring-projects#10083

* Change `payloadType` to `Class<?>`
* Initialize arrays with empty arrays instead of null
* Use `{}` instead of `new T[0]` for empty arrays
* Add missing `@Nullable`

Signed-off-by: Jooyoung Pyoung <[email protected]>

Author: anthologia

spring-integration-websocket/src/main/java/org/springframework/integration/websocket/ClientWebSocketContainer.java

@@ -22,6 +22,8 @@
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.context.Lifecycle;
 import org.springframework.context.SmartLifecycle;
 import org.springframework.http.HttpHeaders;
@@ -60,11 +62,12 @@ public final class ClientWebSocketContainer extends IntegrationWebSocketContaine
 
 	private int connectionTimeout = DEFAULT_CONNECTION_TIMEOUT;
 
+	@SuppressWarnings("NullAway.Init")
 	private volatile CountDownLatch connectionLatch;
 
-	private volatile WebSocketSession clientSession;
+	private volatile @Nullable WebSocketSession clientSession;
 
-	private volatile Throwable openConnectionException;
+	private volatile @Nullable Throwable openConnectionException;
 
 	private volatile boolean connecting;
 
@@ -121,7 +124,7 @@ public void setConnectionTimeout(int connectionTimeout) {
 	 * @return the {@link #clientSession}, if established.
 	 */
 	@Override
-	public WebSocketSession getSession(String sessionId) {
+	public WebSocketSession getSession(@Nullable String sessionId) {
 		if (isRunning()) {
 			if (!isConnected() && !this.connecting) {
 				stop();

spring-integration-websocket/src/main/java/org/springframework/integration/websocket/IntegrationWebSocketContainer.java

@@ -27,9 +27,9 @@
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.beans.factory.DisposableBean;
-import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ReflectionUtils;
 import org.springframework.web.socket.CloseStatus;
@@ -80,14 +80,13 @@ public abstract class IntegrationWebSocketContainer implements DisposableBean {
 
 	private final List<String> supportedProtocols = new ArrayList<>();
 
-	private WebSocketListener messageListener;
+	private @Nullable WebSocketListener messageListener;
 
 	private int sendTimeLimit = DEFAULT_SEND_TIME_LIMIT;
 
 	private int sendBufferSizeLimit = DEFAULT_SEND_BUFFER_SIZE;
 
-	@Nullable
-	private ConcurrentWebSocketSessionDecorator.OverflowStrategy sendBufferOverflowStrategy;
+	private ConcurrentWebSocketSessionDecorator.@Nullable OverflowStrategy sendBufferOverflowStrategy;
 
 	public void setSendTimeLimit(int sendTimeLimit) {
 		this.sendTimeLimit = sendTimeLimit;
@@ -107,7 +106,7 @@ public void setSendBufferSizeLimit(int sendBufferSizeLimit) {
 	 * @see ConcurrentWebSocketSessionDecorator
 	 */
 	public void setSendBufferOverflowStrategy(
-			@Nullable ConcurrentWebSocketSessionDecorator.OverflowStrategy overflowStrategy) {
+			ConcurrentWebSocketSessionDecorator.@Nullable OverflowStrategy overflowStrategy) {
 
 		this.sendBufferOverflowStrategy = overflowStrategy;
 	}
@@ -155,7 +154,7 @@ public Map<String, WebSocketSession> getSessions() {
 		return Collections.unmodifiableMap(this.sessions);
 	}
 
-	public WebSocketSession getSession(String sessionId) {
+	public WebSocketSession getSession(@Nullable String sessionId) {
 		WebSocketSession session = this.sessions.get(sessionId);
 		Assert.notNull(session, () -> "Session not found for id '" + sessionId + "'");
 		return session;

spring-integration-websocket/src/main/java/org/springframework/integration/websocket/ServerWebSocketContainer.java

@@ -18,6 +18,8 @@
 
 import java.util.Arrays;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.context.Lifecycle;
 import org.springframework.context.SmartLifecycle;
 import org.springframework.integration.JavaUtils;
@@ -48,6 +50,7 @@
  * @author Artem Bilan
  * @author Gary Russell
  * @author Christian Tzolov
+ * @author Jooyoung Pyoung
  *
  * @since 4.1
  */
@@ -56,21 +59,21 @@ public class ServerWebSocketContainer extends IntegrationWebSocketContainer
 
 	private final String[] paths;
 
-	private HandshakeHandler handshakeHandler;
+	private @Nullable HandshakeHandler handshakeHandler;
 
-	private HandshakeInterceptor[] interceptors;
+	private HandshakeInterceptor[] interceptors = {};
 
-	private WebSocketHandlerDecoratorFactory[] decoratorFactories;
+	private WebSocketHandlerDecoratorFactory @Nullable [] decoratorFactories;
 
-	private SockJsServiceOptions sockJsServiceOptions;
+	private @Nullable SockJsServiceOptions sockJsServiceOptions;
 
-	private String[] origins;
+	private String[] origins = {};
 
 	private boolean autoStartup = true;
 
 	private int phase = 0;
 
-	private TaskScheduler sockJsTaskScheduler;
+	private @Nullable TaskScheduler sockJsTaskScheduler;
 
 	public ServerWebSocketContainer(String... paths) {
 		Assert.notEmpty(paths, "'paths' must not be empty");
@@ -144,7 +147,7 @@ public void setSockJsTaskScheduler(TaskScheduler sockJsTaskScheduler) {
 		this.sockJsTaskScheduler = sockJsTaskScheduler;
 	}
 
-	public TaskScheduler getSockJsTaskScheduler() {
+	public @Nullable TaskScheduler getSockJsTaskScheduler() {
 		return this.sockJsTaskScheduler;
 	}
 
@@ -159,19 +162,25 @@ public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
 			}
 		}
 
+		Assert.notNull(this.handshakeHandler, "'handshakeHandler' must not be null");
 		WebSocketHandlerRegistration registration = registry.addHandler(webSocketHandler, this.paths)
-				.setHandshakeHandler(this.handshakeHandler)
-				.addInterceptors(this.interceptors)
-				.setAllowedOrigins(this.origins);
+				.setHandshakeHandler(this.handshakeHandler);
 
+		configureRegistration(registration);
 		configureSockJsOptionsIfAny(registration);
 	}
 
+	private void configureRegistration(WebSocketHandlerRegistration registration) {
+		registration.addInterceptors(this.interceptors);
+		registration.setAllowedOrigins(this.origins);
+	}
+
 	private void configureSockJsOptionsIfAny(WebSocketHandlerRegistration registration) {
 		if (this.sockJsServiceOptions != null) {
 			SockJsServiceRegistration sockJsServiceRegistration = registration.withSockJS();
 			JavaUtils.INSTANCE
-					.acceptIfCondition(this.sockJsServiceOptions.taskScheduler == null,
+					.acceptIfCondition(this.sockJsServiceOptions.taskScheduler == null &&
+									this.sockJsTaskScheduler != null,
 							this.sockJsTaskScheduler, this.sockJsServiceOptions::setTaskScheduler)
 					.acceptIfNotNull(this.sockJsServiceOptions.webSocketEnabled,
 							sockJsServiceRegistration::setWebSocketEnabled)
@@ -227,8 +236,8 @@ public boolean isRunning() {
 	public void start() {
 		this.lock.lock();
 		try {
-			if (this.handshakeHandler instanceof Lifecycle && !isRunning()) {
-				((Lifecycle) this.handshakeHandler).start();
+			if (this.handshakeHandler instanceof Lifecycle lifeCycleHandler && !isRunning()) {
+				lifeCycleHandler.start();
 			}
 		}
 		finally {
@@ -238,15 +247,15 @@ public void start() {
 
 	@Override
 	public void stop() {
-		if (isRunning()) {
-			((Lifecycle) this.handshakeHandler).stop();
+		if (this.handshakeHandler instanceof Lifecycle lifeCycleHandler && isRunning()) {
+			lifeCycleHandler.stop();
 		}
 	}
 
 	@Override
 	public void stop(Runnable callback) {
-		if (isRunning()) {
-			((Lifecycle) this.handshakeHandler).stop();
+		if (this.handshakeHandler instanceof Lifecycle lifeCycleHandler && isRunning()) {
+			lifeCycleHandler.stop();
 		}
 		callback.run();
 	}
@@ -256,27 +265,27 @@ public void stop(Runnable callback) {
 	 */
 	public static class SockJsServiceOptions {
 
-		private TaskScheduler taskScheduler;
+		private @Nullable TaskScheduler taskScheduler;
 
-		private String clientLibraryUrl;
+		private @Nullable String clientLibraryUrl;
 
-		private Integer streamBytesLimit;
+		private @Nullable Integer streamBytesLimit;
 
-		private Boolean sessionCookieNeeded;
+		private @Nullable Boolean sessionCookieNeeded;
 
-		private Long heartbeatTime;
+		private @Nullable Long heartbeatTime;
 
-		private Long disconnectDelay;
+		private @Nullable Long disconnectDelay;
 
-		private Integer httpMessageCacheSize;
+		private @Nullable Integer httpMessageCacheSize;
 
-		private Boolean webSocketEnabled;
+		private @Nullable Boolean webSocketEnabled;
 
-		private TransportHandler[] transportHandlers;
+		private TransportHandler @Nullable [] transportHandlers;
 
-		private SockJsMessageCodec messageCodec;
+		private @Nullable SockJsMessageCodec messageCodec;
 
-		private Boolean suppressCors;
+		private @Nullable Boolean suppressCors;
 
 		public SockJsServiceOptions setTaskScheduler(TaskScheduler taskScheduler) {
 			this.taskScheduler = taskScheduler;

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

@@ -49,10 +49,13 @@ class IntegrationServletWebSocketHandlerRegistry extends ServletWebSocketHandler
 
 	private final Map<WebSocketHandler, List<String>> dynamicRegistrations = new HashMap<>();
 
+	@SuppressWarnings("NullAway.Init")
 	private ApplicationContext applicationContext;
 
+	@SuppressWarnings("NullAway.Init")
 	private TaskScheduler sockJsTaskScheduler;
 
+	@SuppressWarnings("NullAway.Init")
 	private volatile IntegrationDynamicWebSocketHandlerMapping dynamicHandlerMapping;
 
 	IntegrationServletWebSocketHandlerRegistry() {
@@ -124,6 +127,7 @@ void removeRegistration(ServerWebSocketContainer serverWebSocketContainer) {
 
 	private static final class DynamicHandlerRegistrationProxy implements WebSocketHandlerRegistry {
 
+		@SuppressWarnings("NullAway.Init")
 		private IntegrationDynamicWebSocketHandlerRegistration registration;
 
 		DynamicHandlerRegistrationProxy() {
@@ -141,6 +145,7 @@ public WebSocketHandlerRegistration addHandler(WebSocketHandler webSocketHandler
 	private static final class IntegrationDynamicWebSocketHandlerRegistration
 			extends ServletWebSocketHandlerRegistration {
 
+		@SuppressWarnings("NullAway.Init")
 		private WebSocketHandler handler;
 
 		IntegrationDynamicWebSocketHandlerRegistration() {

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

@@ -120,8 +120,10 @@ private void registerEnableWebSocketIfNecessary(BeanDefinitionRegistry registry)
 
 	static class WebSocketHandlerMappingFactoryBean extends AbstractFactoryBean<HandlerMapping> {
 
+		@SuppressWarnings("NullAway.Init")
 		private IntegrationServletWebSocketHandlerRegistry registry;
 
+		@SuppressWarnings("NullAway.Init")
 		private ThreadPoolTaskScheduler sockJsTaskScheduler;
 
 		public void setRegistry(IntegrationServletWebSocketHandlerRegistry registry) {

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

@@ -1,4 +1,6 @@
 /**
  * Contains parser classes for the WebSockets namespace support.
  */
+
+@org.jspecify.annotations.NullMarked
 package org.springframework.integration.websocket.config;

spring-integration-websocket/src/main/java/org/springframework/integration/websocket/event/package-info.java

@@ -0,0 +1,6 @@
+/**
+ * Provides classes which represent WebSocket event components.
+ */
+
+@org.jspecify.annotations.NullMarked
+package org.springframework.integration.websocket.event;

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

@@ -21,7 +21,8 @@
 import java.util.List;
 import java.util.ListIterator;
 import java.util.Map;
-import java.util.concurrent.atomic.AtomicReference;
+
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.context.ApplicationEventPublisher;
 import org.springframework.context.ApplicationEventPublisherAware;
@@ -67,6 +68,7 @@
  *
  * @author Artem Bilan
  * @author Ngoc Nhan
+ * @author Jooyoung Pyoung
  *
  * @since 4.1
  */
@@ -99,17 +101,18 @@ public class WebSocketInboundChannelAdapter extends MessageProducerSupport
 
 	private final MessageChannel subProtocolHandlerChannel;
 
-	private final AtomicReference<Class<?>> payloadType = new AtomicReference<>(String.class);
+	private Class<?> payloadType = String.class;
 
+	@SuppressWarnings("NullAway.Init")
 	private ApplicationEventPublisher eventPublisher;
 
-	private List<MessageConverter> messageConverters;
+	private @Nullable List<MessageConverter> messageConverters;
 
 	private boolean mergeWithDefaultConverters = false;
 
 	private boolean useBroker;
 
-	private AbstractBrokerMessageHandler brokerHandler;
+	private @Nullable AbstractBrokerMessageHandler brokerHandler;
 
 	public WebSocketInboundChannelAdapter(IntegrationWebSocketContainer webSocketContainer) {
 		this(webSocketContainer, new SubProtocolHandlerRegistry(new PassThruSubProtocolHandler()));
@@ -163,7 +166,7 @@ public void setMergeWithDefaultConverters(boolean mergeWithDefaultConverters) {
 	 */
 	public void setPayloadType(Class<?> payloadType) {
 		Assert.notNull(payloadType, "'payloadType' must not be null");
-		this.payloadType.set(payloadType);
+		this.payloadType = payloadType;
 	}
 
 	/**
@@ -303,7 +306,7 @@ public boolean isActive() {
 		return active;
 	}
 
-	@SuppressWarnings("unchecked")
+	@SuppressWarnings({"unchecked", "NullAway"}) // Dataflow analysis limitation
 	private void handleMessageAndSend(final Message<?> message) {
 		SimpMessageHeaderAccessor headerAccessor = SimpMessageHeaderAccessor.wrap(message);
 		StompCommand stompCommand = (StompCommand) headerAccessor.getHeader("stompCommand");
@@ -335,8 +338,8 @@ else if (StompCommand.RECEIPT.equals(stompCommand)) {
 		}
 	}
 
-	private boolean isProcessingTypeOrCommand(SimpMessageHeaderAccessor headerAccessor, StompCommand stompCommand,
-			SimpMessageType messageType) {
+	private boolean isProcessingTypeOrCommand(SimpMessageHeaderAccessor headerAccessor, @Nullable StompCommand stompCommand,
+			@Nullable SimpMessageType messageType) {
 
 		return (messageType == null // NOSONAR pretty simple logic
 				|| SimpMessageType.MESSAGE.equals(messageType)
@@ -346,7 +349,8 @@ private boolean isProcessingTypeOrCommand(SimpMessageHeaderAccessor headerAccess
 				&& !checkDestinationPrefix(headerAccessor.getDestination());
 	}
 
-	private boolean checkDestinationPrefix(String destination) {
+	@SuppressWarnings("NullAway") // Dataflow analysis limitation
+	private boolean checkDestinationPrefix(@Nullable String destination) {
 		if (this.useBroker) {
 			Collection<String> destinationPrefixes = this.brokerHandler.getDestinationPrefixes();
 			if ((destination == null) || CollectionUtils.isEmpty(destinationPrefixes)) {
@@ -374,11 +378,11 @@ private void produceConnectAckMessage(Message<?> message, SimpMessageHeaderAcces
 	}
 
 	private void produceMessage(Message<?> message, SimpMessageHeaderAccessor headerAccessor) {
-		Object payload = this.messageConverter.fromMessage(message, this.payloadType.get());
+		Object payload = this.messageConverter.fromMessage(message, this.payloadType);
 		Assert.state(payload != null,
 				() -> "The message converter '" + this.messageConverter +
 						"' produced no payload for message '" + message +
-						"' and expected payload type: " + this.payloadType.get());
+						"' and expected payload type: " + this.payloadType);
 		Message<Object> messageToSend =
 				getMessageBuilderFactory()
 						.withPayload(payload)

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

@@ -1,4 +1,6 @@
 /**
  * Provides classes which represent inbound WebSocket components.
  */
+
+@org.jspecify.annotations.NullMarked
 package org.springframework.integration.websocket.inbound;