Use Map.computeIfAbsent() where feasible

See gh-31916

spring-beans/src/test/java/org/springframework/beans/factory/FactoryBeanTests.java

@@ -284,11 +284,7 @@ public class FactoryBeanTests {
 			if (bean instanceof FactoryBean) {
 				return bean;
 			}
-			AtomicInteger c = count.get(beanName);
-			if (c == null) {
-				c = new AtomicInteger();
-				count.put(beanName, c);
-			}
+			AtomicInteger c = count.computeIfAbsent(beanName, k -> new AtomicInteger());
 			c.incrementAndGet();
 			return bean;
 		}

spring-websocket/src/main/java/org/springframework/web/socket/server/standard/SpringConfigurator.java

@@ -102,11 +102,7 @@ public class SpringConfigurator extends Configurator {
 	private String getBeanNameByType(WebApplicationContext wac, Class<?> endpointClass) {
 		String wacId = wac.getId();
 
-		Map<Class<?>, String> beanNamesByType = cache.get(wacId);
-		if (beanNamesByType == null) {
-			beanNamesByType = new ConcurrentHashMap<>();
-			cache.put(wacId, beanNamesByType);
-		}
+		Map<Class<?>, String> beanNamesByType = cache.computeIfAbsent(wacId, k -> new ConcurrentHashMap<>());
 
 		if (!beanNamesByType.containsKey(endpointClass)) {
 			String[] names = wac.getBeanNamesForType(endpointClass);