Simplify getCache() implementation in CaffeineCacheManager

Closes gh-24376

spring-context-support/src/main/java/org/springframework/cache/caffeine/CaffeineCacheManager.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * 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.
@@ -50,6 +50,7 @@ import org.springframework.util.ObjectUtils;
  * @author Ben Manes
  * @author Juergen Hoeller
  * @author Stephane Nicoll
+ * @author Sam Brannen
  * @since 4.3
  * @see CaffeineCache
  */
@@ -178,17 +179,8 @@ public class CaffeineCacheManager implements CacheManager {
 	@Override
 	@Nullable
 	public Cache getCache(String name) {
-		Cache cache = this.cacheMap.get(name);
-		if (cache == null && this.dynamic) {
-			synchronized (this.cacheMap) {
-				cache = this.cacheMap.get(name);
-				if (cache == null) {
-					cache = createCaffeineCache(name);
-					this.cacheMap.put(name, cache);
-				}
-			}
-		}
-		return cache;
+		return this.cacheMap.computeIfAbsent(name, cacheName ->
+				this.dynamic ? createCaffeineCache(cacheName) : null);
 	}
 
 	/**