Fold DefaultWebSession within InMemoryWebSessionStore

InMemoryWebSessionStore is very closely associated to DefaultWebSession
passing it to it several fields and functions. Now that the store also
creates the session, it makes sense to bring the latter in as an inner,
nested class.

Issue: SPR-15875, 15876

Author: rstoyanchev

spring-web/src/main/java/org/springframework/web/server/session/DefaultWebSession.java

@@ -16,16 +16,18 @@
 package org.springframework.web.server.session;
 
 import java.time.Clock;
+import java.time.Duration;
 import java.time.Instant;
 import java.time.ZoneId;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicReference;
+
+import reactor.core.publisher.Mono;
 
 import org.springframework.util.Assert;
 import org.springframework.util.IdGenerator;
 import org.springframework.util.JdkIdGenerator;
-import reactor.core.publisher.Mono;
-
 import org.springframework.web.server.WebSession;
 
 /**
@@ -67,6 +69,11 @@ public Clock getClock() {
 	}
 
 
+	@Override
+	public Mono<WebSession> createWebSession() {
+		return Mono.fromSupplier(InMemoryWebSession::new);
+	}
+
 	@Override
 	public Mono<WebSession> retrieveSession(String id) {
 		return (this.sessions.containsKey(id) ? Mono.just(this.sessions.get(id)) : Mono.empty());
@@ -78,21 +85,16 @@ public Mono<Void> removeSession(String id) {
 		return Mono.empty();
 	}
 
-	public Mono<WebSession> createWebSession() {
-		return Mono.fromSupplier(() ->
-				new DefaultWebSession(idGenerator, getClock(),
-						(oldId, session) -> this.changeSessionId(oldId, session),
-						this::storeSession));
-	}
-
 	public Mono<WebSession> updateLastAccessTime(WebSession webSession) {
 		return Mono.fromSupplier(() -> {
-			DefaultWebSession session = (DefaultWebSession) webSession;
+			InMemoryWebSession session = (InMemoryWebSession) webSession;
 			Instant lastAccessTime = Instant.now(getClock());
-			return new DefaultWebSession(session, lastAccessTime);
+			return new InMemoryWebSession(session, lastAccessTime);
 		});
 	}
 
+	/* Private methods for InMemoryWebSession */
+
 	private Mono<Void> changeSessionId(String oldId, WebSession session) {
 		this.sessions.remove(oldId);
 		this.sessions.put(session.getId(), session);
@@ -103,4 +105,100 @@ private Mono<Void> storeSession(WebSession session) {
 		this.sessions.put(session.getId(), session);
 		return Mono.empty();
 	}
+
+
+	private class InMemoryWebSession implements WebSession {
+
+		private final AtomicReference<String> id;
+
+		private final Map<String, Object> attributes;
+
+		private final Instant creationTime;
+
+		private final Instant lastAccessTime;
+
+		private volatile Duration maxIdleTime;
+
+		private volatile boolean started;
+
+
+		InMemoryWebSession() {
+			this.id = new AtomicReference<>(String.valueOf(idGenerator.generateId()));
+			this.attributes = new ConcurrentHashMap<>();
+			this.creationTime = Instant.now(getClock());
+			this.lastAccessTime = this.creationTime;
+			this.maxIdleTime = Duration.ofMinutes(30);
+		}
+
+		InMemoryWebSession(InMemoryWebSession existingSession, Instant lastAccessTime) {
+			this.id = existingSession.id;
+			this.attributes = existingSession.attributes;
+			this.creationTime = existingSession.creationTime;
+			this.lastAccessTime = lastAccessTime;
+			this.maxIdleTime = existingSession.maxIdleTime;
+			this.started = existingSession.isStarted(); // Use method (explicit or implicit start)
+		}
+
+
+		@Override
+		public String getId() {
+			return this.id.get();
+		}
+
+		@Override
+		public Map<String, Object> getAttributes() {
+			return this.attributes;
+		}
+
+		@Override
+		public Instant getCreationTime() {
+			return this.creationTime;
+		}
+
+		@Override
+		public Instant getLastAccessTime() {
+			return this.lastAccessTime;
+		}
+
+		@Override
+		public void setMaxIdleTime(Duration maxIdleTime) {
+			this.maxIdleTime = maxIdleTime;
+		}
+
+		@Override
+		public Duration getMaxIdleTime() {
+			return this.maxIdleTime;
+		}
+
+
+		@Override
+		public void start() {
+			this.started = true;
+		}
+
+		@Override
+		public boolean isStarted() {
+			return this.started || !getAttributes().isEmpty();
+		}
+
+		@Override
+		public Mono<Void> changeSessionId() {
+			String oldId = this.id.get();
+			String newId = String.valueOf(idGenerator.generateId());
+			this.id.set(newId);
+			return InMemoryWebSessionStore.this.changeSessionId(oldId, this).doOnError(ex -> this.id.set(oldId));
+		}
+
+		@Override
+		public Mono<Void> save() {
+			return InMemoryWebSessionStore.this.storeSession(this);
+		}
+
+		@Override
+		public boolean isExpired() {
+			return (isStarted() && !this.maxIdleTime.isNegative() &&
+					Instant.now(getClock()).minus(this.maxIdleTime).isAfter(this.lastAccessTime));
+		}
+	}
+
 }