Nullability fine-tuning around declaration inconsistencies

Issue: SPR-15720
Issue: SPR-15792

spring-messaging/src/main/java/org/springframework/messaging/converter/DefaultContentTypeResolver.java

@@ -32,6 +32,7 @@ import org.springframework.util.MimeType;
  */
 public class DefaultContentTypeResolver implements ContentTypeResolver {
 
+	@Nullable
 	private MimeType defaultMimeType;
 
 
@@ -40,7 +41,7 @@ public class DefaultContentTypeResolver implements ContentTypeResolver {
 	 * {@link MessageHeaders#CONTENT_TYPE} header present.
 	 * <p>This property does not have a default value.
 	 */
-	public void setDefaultMimeType(MimeType defaultMimeType) {
+	public void setDefaultMimeType(@Nullable MimeType defaultMimeType) {
 		this.defaultMimeType = defaultMimeType;
 	}
 
@@ -48,6 +49,7 @@ public class DefaultContentTypeResolver implements ContentTypeResolver {
 	 * Return the default MIME type to use if no
 	 * {@link MessageHeaders#CONTENT_TYPE} header is present.
 	 */
+	@Nullable
 	public MimeType getDefaultMimeType() {
 		return this.defaultMimeType;
 	}

spring-messaging/src/main/java/org/springframework/messaging/core/GenericMessagingTemplate.java

@@ -276,6 +276,7 @@ public class GenericMessagingTemplate extends AbstractDestinationResolvingMessag
 
 		private final boolean throwExceptionOnLateReply;
 
+		@Nullable
 		private volatile Message<?> replyMessage;
 
 		private volatile boolean hasReceived;

spring-messaging/src/main/java/org/springframework/messaging/simp/broker/AbstractBrokerMessageHandler.java

@@ -283,7 +283,9 @@ public abstract class AbstractBrokerMessageHandler
 	private class UnsentDisconnectChannelInterceptor extends ChannelInterceptorAdapter {
 
 		@Override
-		public void afterSendCompletion(Message<?> message, MessageChannel channel, boolean sent, Exception ex) {
+		public void afterSendCompletion(
+				Message<?> message, MessageChannel channel, boolean sent, @Nullable Exception ex) {
+
 			if (!sent) {
 				SimpMessageType messageType = SimpMessageHeaderAccessor.getMessageType(message.getHeaders());
 				if (SimpMessageType.DISCONNECT.equals(messageType)) {

spring-messaging/src/main/java/org/springframework/messaging/simp/stomp/DefaultStompSession.java

@@ -548,6 +548,7 @@ public class DefaultStompSession implements ConnectionHandlingStompSession {
 		}
 
 		@Override
+		@Nullable
 		public String getReceiptId() {
 			return this.receiptId;
 		}

spring-messaging/src/main/java/org/springframework/messaging/simp/stomp/StompHeaderAccessor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -256,7 +256,7 @@ public class StompHeaderAccessor extends SimpMessageHeaderAccessor {
 	}
 
 	@Override
-	public void setDestination(String destination) {
+	public void setDestination(@Nullable String destination) {
 		super.setDestination(destination);
 		setNativeHeader(STOMP_DESTINATION_HEADER, destination);
 	}

spring-messaging/src/main/java/org/springframework/messaging/simp/user/MultiServerUserRegistry.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -18,6 +18,7 @@ package org.springframework.messaging.simp.user;
 
 import java.net.InetAddress;
 import java.net.UnknownHostException;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
@@ -195,9 +196,9 @@ public class MultiServerUserRegistry implements SimpUserRegistry, SmartApplicati
 	 */
 	private static class UserRegistrySnapshot {
 
-		private String id;
+		private String id = "";
 
-		private Map<String, TransferSimpUser> users;
+		private Map<String, TransferSimpUser> users = Collections.emptyMap();
 
 		private long expirationTime;
 
@@ -273,12 +274,12 @@ public class MultiServerUserRegistry implements SimpUserRegistry, SmartApplicati
 	 */
 	private static class TransferSimpUser implements SimpUser {
 
-		private String name;
+		private String name = "";
 
-		/* User sessions from "this" registry only (i.e. one server) */
+		// User sessions from "this" registry only (i.e. one server)
 		private Set<TransferSimpSession> sessions;
 
-		/* Cross-server session lookup (e.g. user connected to multiple servers) */
+		// Cross-server session lookup (e.g. user connected to multiple servers)
 		@Nullable
 		private SessionLookup sessionLookup;
 
@@ -393,6 +394,8 @@ public class MultiServerUserRegistry implements SimpUserRegistry, SmartApplicati
 		 */
 		@SuppressWarnings("unused")
 		public TransferSimpSession() {
+			this.id = "";
+			this.user = new TransferSimpUser();
 			this.subscriptions = new HashSet<>(4);
 		}
 
@@ -401,6 +404,7 @@ public class MultiServerUserRegistry implements SimpUserRegistry, SmartApplicati
 		 */
 		public TransferSimpSession(SimpSession session) {
 			this.id = session.getId();
+			this.user = new TransferSimpUser();
 			Set<SimpSubscription> subscriptions = session.getSubscriptions();
 			this.subscriptions = new HashSet<>(subscriptions.size());
 			for (SimpSubscription subscription : subscriptions) {
@@ -443,12 +447,12 @@ public class MultiServerUserRegistry implements SimpUserRegistry, SmartApplicati
 
 		@Override
 		public boolean equals(Object other) {
-			return (this == other || (other instanceof SimpSession && this.id.equals(((SimpSession) other).getId())));
+			return (this == other || (other instanceof SimpSession && getId().equals(((SimpSession) other).getId())));
 		}
 
 		@Override
 		public int hashCode() {
-			return this.id.hashCode();
+			return getId().hashCode();
 		}
 
 		@Override
@@ -474,6 +478,9 @@ public class MultiServerUserRegistry implements SimpUserRegistry, SmartApplicati
 		 */
 		@SuppressWarnings("unused")
 		public TransferSimpSubscription() {
+			this.id = "";
+			this.session = new TransferSimpSession();
+			this.destination = "";
 		}
 
 		/**
@@ -481,6 +488,7 @@ public class MultiServerUserRegistry implements SimpUserRegistry, SmartApplicati
 		 */
 		public TransferSimpSubscription(SimpSubscription subscription) {
 			this.id = subscription.getId();
+			this.session = new TransferSimpSession();
 			this.destination = subscription.getDestination();
 		}
 
@@ -520,13 +528,13 @@ public class MultiServerUserRegistry implements SimpUserRegistry, SmartApplicati
 				return false;
 			}
 			SimpSubscription otherSubscription = (SimpSubscription) other;
-			return (ObjectUtils.nullSafeEquals(getSession(), otherSubscription.getSession()) &&
-					this.id.equals(otherSubscription.getId()));
+			return (getId().equals(otherSubscription.getId()) &&
+					ObjectUtils.nullSafeEquals(getSession(), otherSubscription.getSession()));
 		}
 
 		@Override
 		public int hashCode() {
-			return this.id.hashCode() * 31 + ObjectUtils.nullSafeHashCode(getSession());
+			return getId().hashCode() * 31 + ObjectUtils.nullSafeHashCode(getSession());
 		}
 
 		@Override

spring-messaging/src/main/java/org/springframework/messaging/simp/user/SimpSession.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -18,6 +18,8 @@ package org.springframework.messaging.simp.user;
 
 import java.util.Set;
 
+import org.springframework.lang.Nullable;
+
 /**
  * Represents a session of connected user.
  *

spring-messaging/src/main/java/org/springframework/messaging/simp/user/SimpSubscription.java

@@ -16,6 +16,8 @@
 
 package org.springframework.messaging.simp.user;
 
+import org.springframework.lang.Nullable;
+
 /**
  * Represents a subscription within a user session.
  *
@@ -25,17 +27,17 @@ package org.springframework.messaging.simp.user;
 public interface SimpSubscription {
 
 	/**
-	 * Return the id associated of the subscription (never {@code null}).
+	 * Return the id associated of the subscription.
 	 */
 	String getId();
 
 	/**
-	 * Return the session of the subscription (never {@code null}).
+	 * Return the session of the subscription.
 	 */
 	SimpSession getSession();
 
 	/**
-	 * Return the subscription's destination (never {@code null}).
+	 * Return the subscription's destination.
 	 */
 	String getDestination();
 

spring-messaging/src/main/java/org/springframework/messaging/support/ChannelInterceptorAdapter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -16,6 +16,7 @@
 
 package org.springframework.messaging.support;
 
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageChannel;
 
@@ -39,7 +40,7 @@ public abstract class ChannelInterceptorAdapter implements ChannelInterceptor {
 	}
 
 	@Override
-	public void afterSendCompletion(Message<?> message, MessageChannel channel, boolean sent, Exception ex) {
+	public void afterSendCompletion(Message<?> message, MessageChannel channel, boolean sent, @Nullable Exception ex) {
 	}
 
 	public boolean preReceive(MessageChannel channel) {
@@ -52,7 +53,7 @@ public abstract class ChannelInterceptorAdapter implements ChannelInterceptor {
 	}
 
 	@Override
-	public void afterReceiveCompletion(Message<?> message, MessageChannel channel, Exception ex) {
+	public void afterReceiveCompletion(@Nullable Message<?> message, MessageChannel channel, @Nullable Exception ex) {
 	}
 
 }