From 2f2546c8a454bd63181d793e31acdf0252b3ff4c Mon Sep 17 00:00:00 2001
From: Rossen Stoyanchev <rstoyanchev@pivotal.io>
Date: Thu, 30 Jun 2016 16:00:49 -0400
Subject: [PATCH] Simplify initialization of WebSession Mono

The DefaultWebSessionManager now uses Mono.defer to protect the call
to getSession from parsing session cookies immediately. This allows
pre-initializing the Mono<WebSession> upfront vs using a lock.
---
 .../adapter/DefaultServerWebExchange.java       | 17 ++---------------
 .../session/DefaultWebSessionManager.java       | 13 +++++++------
 2 files changed, 9 insertions(+), 21 deletions(-)

diff --git a/spring-web-reactive/src/main/java/org/springframework/web/server/adapter/DefaultServerWebExchange.java b/spring-web-reactive/src/main/java/org/springframework/web/server/adapter/DefaultServerWebExchange.java
index 295db4f880..bbd7342fca 100644
--- a/spring-web-reactive/src/main/java/org/springframework/web/server/adapter/DefaultServerWebExchange.java
+++ b/spring-web-reactive/src/main/java/org/springframework/web/server/adapter/DefaultServerWebExchange.java
@@ -39,15 +39,9 @@ public class DefaultServerWebExchange implements ServerWebExchange {
 
 	private final ServerHttpResponse response;
 
-	private final WebSessionManager sessionManager;
-
-
 	private final Map<String, Object> attributes = new ConcurrentHashMap<>();
 
-	private final Object createSessionLock = new Object();
-
-	private Mono<WebSession> sessionMono;
-
+	private final Mono<WebSession> sessionMono;
 
 
 	public DefaultServerWebExchange(ServerHttpRequest request, ServerHttpResponse response,
@@ -58,7 +52,7 @@ public class DefaultServerWebExchange implements ServerWebExchange {
 		Assert.notNull(response, "'sessionManager' is required.");
 		this.request = request;
 		this.response = response;
-		this.sessionManager = sessionManager;
+		this.sessionMono = sessionManager.getSession(this).cache();
 	}
 
 
@@ -84,13 +78,6 @@ public class DefaultServerWebExchange implements ServerWebExchange {
 
 	@Override
 	public Mono<WebSession> getSession() {
-		if (this.sessionMono == null) {
-			synchronized (this.createSessionLock) {
-				if (this.sessionMono == null) {
-					this.sessionMono = this.sessionManager.getSession(this).cache();
-				}
-			}
-		}
 		return this.sessionMono;
 	}
 
diff --git a/spring-web-reactive/src/main/java/org/springframework/web/server/session/DefaultWebSessionManager.java b/spring-web-reactive/src/main/java/org/springframework/web/server/session/DefaultWebSessionManager.java
index 64a5e58b2e..6e51319ac2 100644
--- a/spring-web-reactive/src/main/java/org/springframework/web/server/session/DefaultWebSessionManager.java
+++ b/spring-web-reactive/src/main/java/org/springframework/web/server/session/DefaultWebSessionManager.java
@@ -99,12 +99,13 @@ public class DefaultWebSessionManager implements WebSessionManager {
 
 	@Override
 	public Mono<WebSession> getSession(ServerWebExchange exchange) {
-		return Flux.fromIterable(getSessionIdResolver().resolveSessionIds(exchange))
-				.concatMap(this.sessionStore::retrieveSession)
-				.next()
-				.then(session -> validateSession(exchange, session))
-				.otherwiseIfEmpty(createSession(exchange))
-				.map(session -> extendSession(exchange, session));
+		return Mono.defer(() ->
+				Flux.fromIterable(getSessionIdResolver().resolveSessionIds(exchange))
+						.concatMap(this.sessionStore::retrieveSession)
+						.next()
+						.then(session -> validateSession(exchange, session))
+						.otherwiseIfEmpty(createSession(exchange))
+						.map(session -> extendSession(exchange, session)));
 	}
 
 	protected Mono<WebSession> validateSession(ServerWebExchange exchange, WebSession session) {