Introduce ObjectUtils#nullSafeHash(Object... element)

This commit deprecates the various nullSafeHashCode methods taking array
types as they are superseded by Arrays.hashCode now. This means that
the now only remaining nullSafeHashCode method does not trigger a
warning only if the target type is not an array. At the same time, there
are multiple use of this method on several elements, handling the
accumulation of hash codes.

For that reason, this commit also introduces a nullSafeHash that takes
an array of elements. The only difference between Objects.hash is that
this method handles arrays.

The codebase has been reviewed to use any of those two methods when it
is possible.

Closes gh-29051

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

@@ -23,6 +23,7 @@ import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Set;
 import java.util.UUID;
 import java.util.concurrent.ConcurrentHashMap;
@@ -539,7 +540,7 @@ public class MultiServerUserRegistry implements SimpUserRegistry, SmartApplicati
 
 		@Override
 		public int hashCode() {
-			return getId().hashCode() * 31 + ObjectUtils.nullSafeHashCode(getSession());
+			return Objects.hash(getId(), getSession());
 		}
 
 		@Override

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

@@ -98,7 +98,7 @@ public class GenericMessage<T> implements Message<T>, Serializable {
 	@Override
 	public int hashCode() {
 		// Using nullSafeHashCode for proper array hashCode handling
-		return ObjectUtils.nullSafeHashCode(this.payload) * 23 + this.headers.hashCode();
+		return ObjectUtils.nullSafeHash(this.payload, this.headers);
 	}
 
 	@Override

spring-messaging/src/test/java/org/springframework/messaging/simp/user/TestSimpSubscription.java

@@ -16,6 +16,8 @@
 
 package org.springframework.messaging.simp.user;
 
+import java.util.Objects;
+
 import org.springframework.lang.Nullable;
 import org.springframework.util.ObjectUtils;
 
@@ -66,7 +68,7 @@ public class TestSimpSubscription implements SimpSubscription {
 
 	@Override
 	public int hashCode() {
-		return this.id.hashCode() * 31 + ObjectUtils.nullSafeHashCode(getSession());
+		return Objects.hash(this.id, getSession());
 	}
 
 	@Override