Reliable null value handling in ConcurrentMapCache, GuavaCache, JCacheCache

Issue: SPR-13553
(cherry picked from commit de93290)

Author: jhoeller

spring-context-support/src/main/java/org/springframework/cache/jcache/JCacheCache.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2015 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.
@@ -126,6 +126,10 @@ protected Object toStoreValue(Object userValue) {
 
 	@SuppressWarnings("serial")
 	private static class NullHolder implements Serializable {
+
+		private Object readResolve() {
+			return NULL_HOLDER;
+		}
 	}
 
 }

spring-context/src/main/java/org/springframework/cache/concurrent/ConcurrentMapCache.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2015 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.
@@ -16,16 +16,17 @@
 
 package org.springframework.cache.concurrent;
 
-import org.springframework.cache.Cache;
-import org.springframework.cache.support.SimpleValueWrapper;
-
 import java.io.Serializable;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
 
+import org.springframework.cache.Cache;
+import org.springframework.cache.support.SimpleValueWrapper;
+import org.springframework.util.Assert;
+
 /**
- * Simple {@link Cache} implementation based on the core JDK
- * {@code java.util.concurrent} package.
+ * Simple {@link org.springframework.cache.Cache} implementation based on the
+ * core JDK {@code java.util.concurrent} package.
  *
  * <p>Useful for testing or simple caching scenarios, typically in combination
  * with {@link org.springframework.cache.support.SimpleCacheManager} or
@@ -62,21 +63,24 @@ public ConcurrentMapCache(String name) {
 	/**
 	 * Create a new ConcurrentMapCache with the specified name.
 	 * @param name the name of the cache
-	 * @param allowNullValues whether to accept and convert null values for this cache
+	 * @param allowNullValues whether to accept and convert {@code null}
+	 * values for this cache
 	 */
 	public ConcurrentMapCache(String name, boolean allowNullValues) {
 		this(name, new ConcurrentHashMap<Object, Object>(256), allowNullValues);
 	}
 
 	/**
 	 * Create a new ConcurrentMapCache with the specified name and the
-	 * given internal ConcurrentMap to use.
+	 * given internal {@link ConcurrentMap} to use.
 	 * @param name the name of the cache
 	 * @param store the ConcurrentMap to use as an internal store
 	 * @param allowNullValues whether to allow {@code null} values
 	 * (adapting them to an internal null holder value)
 	 */
 	public ConcurrentMapCache(String name, ConcurrentMap<Object, Object> store, boolean allowNullValues) {
+		Assert.notNull(name, "Name must not be null");
+		Assert.notNull(store, "Store must not be null");
 		this.name = name;
 		this.store = store;
 		this.allowNullValues = allowNullValues;
@@ -142,6 +146,10 @@ protected Object toStoreValue(Object userValue) {
 
 	@SuppressWarnings("serial")
 	private static class NullHolder implements Serializable {
+
+		private Object readResolve() {
+			return NULL_HOLDER;
+		}
 	}
 
 }