Use (Concurrent)Map.computeIfAbsent for lazy nested collection creation

spring-core/src/main/java/org/springframework/util/xml/SimpleNamespaceContext.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -123,11 +123,8 @@ public class SimpleNamespaceContext implements NamespaceContext {
 		}
 		else {
 			this.prefixToNamespaceUri.put(prefix, namespaceUri);
-			Set<String> prefixes = this.namespaceUriToPrefixes.get(namespaceUri);
-			if (prefixes == null) {
-				prefixes = new LinkedHashSet<>();
-				this.namespaceUriToPrefixes.put(namespaceUri, prefixes);
-			}
+			Set<String> prefixes =
+					this.namespaceUriToPrefixes.computeIfAbsent(namespaceUri, k -> new LinkedHashSet<>());
 			prefixes.add(prefix);
 		}
 	}

spring-jms/src/main/java/org/springframework/jms/connection/CachingConnectionFactory.java

@@ -26,6 +26,8 @@ import java.util.Iterator;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
 import javax.jms.Connection;
 import javax.jms.ConnectionFactory;
 import javax.jms.Destination;
@@ -86,7 +88,7 @@ public class CachingConnectionFactory extends SingleConnectionFactory {
 
 	private volatile boolean active = true;
 
-	private final Map<Integer, LinkedList<Session>> cachedSessions = new HashMap<>();
+	private final ConcurrentMap<Integer, LinkedList<Session>> cachedSessions = new ConcurrentHashMap<>();
 
 
 	/**
@@ -208,14 +210,7 @@ public class CachingConnectionFactory extends SingleConnectionFactory {
 			return null;
 		}
 
-		LinkedList<Session> sessionList;
-		synchronized (this.cachedSessions) {
-			sessionList = this.cachedSessions.get(mode);
-			if (sessionList == null) {
-				sessionList = new LinkedList<>();
-				this.cachedSessions.put(mode, sessionList);
-			}
-		}
+		LinkedList<Session> sessionList = this.cachedSessions.computeIfAbsent(mode, k -> new LinkedList<>());
 		Session session = null;
 		synchronized (sessionList) {
 			if (!sessionList.isEmpty()) {

spring-jms/src/main/java/org/springframework/jms/connection/JmsResourceHolder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -139,11 +139,7 @@ public class JmsResourceHolder extends ResourceHolderSupport {
 		if (!this.sessions.contains(session)) {
 			this.sessions.add(session);
 			if (connection != null) {
-				List<Session> sessions = this.sessionsPerConnection.get(connection);
-				if (sessions == null) {
-					sessions = new LinkedList<>();
-					this.sessionsPerConnection.put(connection, sessions);
-				}
+				List<Session> sessions = this.sessionsPerConnection.computeIfAbsent(connection, k -> new LinkedList<>());
 				sessions.add(session);
 			}
 		}

spring-messaging/src/main/java/org/springframework/messaging/support/NativeMessageHeaderAccessor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -184,11 +184,7 @@ public class NativeMessageHeaderAccessor extends MessageHeaderAccessor {
 			nativeHeaders = new LinkedMultiValueMap<>(4);
 			setHeader(NATIVE_HEADERS, nativeHeaders);
 		}
-		List<String> values = nativeHeaders.get(name);
-		if (values == null) {
-			values = new LinkedList<>();
-			nativeHeaders.put(name, values);
-		}
+		List<String> values = nativeHeaders.computeIfAbsent(name, k -> new LinkedList<>());
 		values.add(value);
 		setModified(true);
 	}
@@ -197,8 +193,7 @@ public class NativeMessageHeaderAccessor extends MessageHeaderAccessor {
 		if (headers == null) {
 			return;
 		}
-		headers.forEach((key, values) ->
-				values.forEach(value -> addNativeHeader(key, value)));
+		headers.forEach((key, values) -> values.forEach(value -> addNativeHeader(key, value)));
 	}
 
 	@Nullable

spring-test/src/main/java/org/springframework/test/context/cache/DefaultContextCache.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -143,11 +143,7 @@ public class DefaultContextCache implements ContextCache {
 		MergedContextConfiguration child = key;
 		MergedContextConfiguration parent = child.getParent();
 		while (parent != null) {
-			Set<MergedContextConfiguration> list = this.hierarchyMap.get(parent);
-			if (list == null) {
-				list = new HashSet<>();
-				this.hierarchyMap.put(parent, list);
-			}
+			Set<MergedContextConfiguration> list = this.hierarchyMap.computeIfAbsent(parent, k -> new HashSet<>());
 			list.add(child);
 			child = parent;
 			parent = child.getParent();