Proper nullable return declaration for AbstractValueAdaptingCache.lookup

Issue: SPR-15540

spring-context-support/src/main/java/org/springframework/cache/caffeine/CaffeineCache.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.
@@ -100,6 +100,7 @@ public class CaffeineCache extends AbstractValueAdaptingCache {
 	}
 
 	@Override
+	@Nullable
 	protected Object lookup(Object key) {
 		return this.cache.getIfPresent(key);
 	}

spring-context-support/src/main/java/org/springframework/cache/ehcache/EhCacheCache.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 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.
@@ -42,13 +42,15 @@ public class EhCacheCache implements Cache {
 
 	/**
 	 * Create an {@link EhCacheCache} instance.
-	 * @param ehcache backing Ehcache instance
+	 * @param ehcache the backing Ehcache instance
 	 */
 	public EhCacheCache(Ehcache ehcache) {
 		Assert.notNull(ehcache, "Ehcache must not be null");
 		Status status = ehcache.getStatus();
-		Assert.isTrue(Status.STATUS_ALIVE.equals(status),
+		if (!Status.STATUS_ALIVE.equals(status)) {
-				"An 'alive' Ehcache is required - current cache is " + status.toString());
+			throw new IllegalArgumentException(
+					"An 'alive' Ehcache is required - current cache is " + status.toString());
+		}
 		this.cache = ehcache;
 	}
 
@@ -81,7 +83,7 @@ public class EhCacheCache implements Cache {
 		else {
 			this.cache.acquireWriteLockOnKey(key);
 			try {
-				element = lookup(key); // One more attempt with the write lock
+				element = lookup(key);  // one more attempt with the write lock
 				if (element != null) {
 					return (T) element.getObjectValue();
 				}
@@ -115,7 +117,8 @@ public class EhCacheCache implements Cache {
 		Element element = this.cache.get(key);
 		Object value = (element != null ? element.getObjectValue() : null);
 		if (value != null && type != null && !type.isInstance(value)) {
-			throw new IllegalStateException("Cached value is not of required type [" + type.getName() + "]: " + value);
+			throw new IllegalStateException(
+					"Cached value is not of required type [" + type.getName() + "]: " + value);
 		}
 		return (T) value;
 	}

spring-context-support/src/main/java/org/springframework/cache/jcache/JCacheCache.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.
@@ -71,6 +71,7 @@ public class JCacheCache extends AbstractValueAdaptingCache {
 	}
 
 	@Override
+	@Nullable
 	protected Object lookup(Object key) {
 		return this.cache.get(key);
 	}

spring-context/src/main/java/org/springframework/cache/concurrent/ConcurrentMapCache.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.
@@ -132,6 +132,7 @@ public class ConcurrentMapCache extends AbstractValueAdaptingCache {
 	}
 
 	@Override
+	@Nullable
 	protected Object lookup(Object key) {
 		return this.store.get(key);
 	}
@@ -201,8 +202,8 @@ public class ConcurrentMapCache extends AbstractValueAdaptingCache {
 	}
 
 	@Override
-	protected Object fromStoreValue(Object storeValue) {
+	protected Object fromStoreValue(@Nullable Object storeValue) {
-		if (this.serialization != null) {
+		if (storeValue != null && this.serialization != null) {
 			try {
 				return super.fromStoreValue(deserializeValue(this.serialization, storeValue));
 			}

spring-context/src/main/java/org/springframework/cache/support/AbstractValueAdaptingCache.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.
@@ -65,7 +65,8 @@ public abstract class AbstractValueAdaptingCache implements Cache {
 	public <T> T get(Object key, @Nullable Class<T> type) {
 		Object value = fromStoreValue(lookup(key));
 		if (value != null && type != null && !type.isInstance(value)) {
-			throw new IllegalStateException("Cached value is not of required type [" + type.getName() + "]: " + value);
+			throw new IllegalStateException(
+					"Cached value is not of required type [" + type.getName() + "]: " + value);
 		}
 		return (T) value;
 	}
@@ -73,8 +74,9 @@ public abstract class AbstractValueAdaptingCache implements Cache {
 	/**
 	 * Perform an actual lookup in the underlying store.
 	 * @param key the key whose associated value is to be returned
-	 * @return the raw store value for the key
+	 * @return the raw store value for the key, or {@code null} if none
 	 */
+	@Nullable
 	protected abstract Object lookup(Object key);
 
 
@@ -85,7 +87,7 @@ public abstract class AbstractValueAdaptingCache implements Cache {
 	 * @return the value to return to the user
 	 */
 	@Nullable
-	protected Object fromStoreValue(Object storeValue) {
+	protected Object fromStoreValue(@Nullable Object storeValue) {
 		if (this.allowNullValues && storeValue == NullValue.INSTANCE) {
 			return null;
 		}
@@ -104,8 +106,7 @@ public abstract class AbstractValueAdaptingCache implements Cache {
 				return NullValue.INSTANCE;
 			}
 			throw new IllegalArgumentException(
-					String.format("Cache '%s' is configured to not allow null " +
+					"Cache '" + getName() + "' is configured to not allow null values but null was provided");
-							"values but null was provided", getName()));
 		}
 		return userValue;
 	}