Polish SessionIdChangedEvent

Add AbstractSessionEvent; clean up license headers and Javadocs

Fixes: gh-5438

web/src/main/java/org/springframework/security/web/session/HttpSessionIdChangedEvent.java

@@ -1,11 +1,11 @@
 /*
- * Copyright 2004, 2005, 2006 Acegi Technology Pty Limited
+ * Copyright 2002-2020 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.
  * You may obtain a copy of the License at
  *
- *      http://www.apache.org/licenses/LICENSE-2.0
+ *      https://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
@@ -16,33 +16,33 @@
 
 package org.springframework.security.web.session;
 
-import javax.servlet.http.HttpSession;
-
 import org.springframework.security.core.session.SessionIdChangedEvent;
 
+import javax.servlet.http.HttpSession;
+
 /**
- * Published by the {@link HttpSessionEventPublisher} when an {@code HttpSession} id
- * is changed
+ * Published by the {@link HttpSessionEventPublisher} when an {@link HttpSession} ID
+ * is changed.
  *
+ * @since 5.4
  */
 public class HttpSessionIdChangedEvent extends SessionIdChangedEvent {
 	private final String oldSessionId;
-	private final String newSessionid;
-	// ~ Constructors
-	// ===================================================================================================
+	private final String newSessionId;
 
 	public HttpSessionIdChangedEvent(HttpSession session, String oldSessionId) {
 		super(session);
 		this.oldSessionId = oldSessionId;
-		this.newSessionid = session.getId();
+		this.newSessionId = session.getId();
 	}
 
+	@Override
 	public String getOldSessionId() {
 		return oldSessionId;
 	}
 
 	@Override
 	public String getNewSessionId() {
-		return newSessionid;
+		return newSessionId;
 	}
 }