Added get(key, type) method to Cache interface

This new get variant not only allows for generically specifying the required value type; it also skips the ValueWrapper that the standard get method returns. Note that it is not possible to differentiate between non-existing cache entries and cached null values that way; for that purpose, the standard get variant needs to be used.

Issue: SPR-11061

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

 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2013 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.
@@ -65,6 +65,17 @@ public class EhCacheCache implements Cache {
 		return (element != null ? new SimpleValueWrapper(element.getObjectValue()) : null);
 	}
 
+	@Override
+	@SuppressWarnings("unchecked")
+	public <T> T get(Object key, Class<T> type) {
+		Element element = this.cache.get(key);
+		Object value = (element != null ? element.getObjectValue() : null);
+		if (type != null && !type.isInstance(value)) {
+			throw new IllegalStateException("Cached value is not of required type [" + type.getName() + "]: " + value);
+		}
+		return (T) value;
+	}
+
 	@Override
 	public void put(Object key, Object value) {
 		this.cache.put(new Element(key, value));

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

@@ -82,6 +82,16 @@ public class JCacheCache implements Cache {
 		return (value != null ? new SimpleValueWrapper(fromStoreValue(value)) : null);
 	}
 
+	@Override
+	@SuppressWarnings("unchecked")
+	public <T> T get(Object key, Class<T> type) {
+		Object value = fromStoreValue(this.cache.get(key));
+		if (type != null && !type.isInstance(value)) {
+			throw new IllegalStateException("Cached value is not of required type [" + type.getName() + "]: " + value);
+		}
+		return (T) value;
+	}
+
 	@Override
 	@SuppressWarnings("unchecked")
 	public void put(Object key, Object value) {

spring-context-support/src/main/java/org/springframework/cache/transaction/TransactionAwareCacheDecorator.java

 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2013 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.
@@ -62,6 +62,11 @@ public class TransactionAwareCacheDecorator implements Cache {
 		return this.targetCache.get(key);
 	}
 
+	@Override
+	public <T> T get(Object key, Class<T> type) {
+		return this.targetCache.get(key, type);
+	}
+
 	@Override
 	public void put(final Object key, final Object value) {
 		if (TransactionSynchronizationManager.isSynchronizationActive()) {

spring-context-support/src/test/java/org/springframework/cache/ehcache/EhCacheCacheTests.java

@@ -20,7 +20,6 @@ import net.sf.ehcache.CacheManager;
 import net.sf.ehcache.Ehcache;
 import net.sf.ehcache.Element;
 import net.sf.ehcache.config.CacheConfiguration;
-
 import org.junit.Before;
 import org.junit.Test;
 
@@ -74,6 +73,9 @@ public class EhCacheCacheTests {
 		assertNull(cache.get(key));
 		cache.put(key, value);
 		assertEquals(value, cache.get(key).get());
+		assertEquals(value, cache.get(key, String.class));
+		assertEquals(value, cache.get(key, Object.class));
+		assertEquals(value, cache.get(key, null));
 	}
 
 	@Test

spring-context/src/main/java/org/springframework/cache/Cache.java

 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2013 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.
@@ -39,14 +39,34 @@ public interface Cache {
 	Object getNativeCache();
 
 	/**
-	 * Return the value to which this cache maps the specified key. Returns
-	 * {@code null} if the cache contains no mapping for this key.
-	 * @param key key whose associated value is to be returned.
+	 * Return the value to which this cache maps the specified key.
+	 * <p>Returns {@code null} if the cache contains no mapping for this key;
+	 * otherwise, the cached value (which may be {@code null} itself) will
+	 * be returned in a {@link ValueWrapper}.
+	 * @param key the key whose associated value is to be returned
 	 * @return the value to which this cache maps the specified key,
-	 * or {@code null} if the cache contains no mapping for this key
+	 * contained within a {@link ValueWrapper} which may also hold
+	 * a cached {@code null} value. A straight {@code null} being
+	 * returned means that the cache contains no mapping for this key.
+	 * @see #get(Object, Class)
 	 */
 	ValueWrapper get(Object key);
 
+	/**
+	 * Return the value to which this cache maps the specified key,
+	 * generically specifying a type that return value will be cast to.
+	 * <p>Note: This variant of {@code get} does not allow for differentiating
+	 * between a cached {@code null} value and no cache entry found at all.
+	 * Use the standard {@link #get(Object)} variant for that purpose instead.
+	 * @param key the key whose associated value is to be returned
+	 * @param type the required type of the returned value
+	 * @return the value to which this cache maps the specified key
+	 * (which may be {@code null} itself), or also {@code null} if
+	 * the cache contains no mapping for this key
+	 * @see #get(Object)
+	 */
+	<T> T get(Object key, Class<T> type);
+
 	/**
 	 * Associate the specified value with the specified key in this cache.
 	 * <p>If the cache previously contained a mapping for this key, the old

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

@@ -16,13 +16,13 @@
 
 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;
+
 /**
  * Simple {@link Cache} implementation based on the core JDK
  * {@code java.util.concurrent} package.
@@ -103,6 +103,16 @@ public class ConcurrentMapCache implements Cache {
 		return (value != null ? new SimpleValueWrapper(fromStoreValue(value)) : null);
 	}
 
+	@Override
+	@SuppressWarnings("unchecked")
+	public <T> T get(Object key, Class<T> type) {
+		Object value = fromStoreValue(this.store.get(key));
+		if (type != null && !type.isInstance(value)) {
+			throw new IllegalStateException("Cached value is not of required type [" + type.getName() + "]: " + value);
+		}
+		return (T) value;
+	}
+
 	@Override
 	public void put(Object key, Object value) {
 		this.store.put(key, toStoreValue(value));

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

 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2013 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.
@@ -93,6 +93,11 @@ public class NoOpCacheManager implements CacheManager {
 			return null;
 		}
 
+		@Override
+		public <T> T get(Object key, Class<T> type) {
+			return null;
+		}
+
 		@Override
 		public String getName() {
 			return this.name;

spring-context/src/test/java/org/springframework/cache/NoOpCacheManagerTests.java

 /*
- * Copyright 2011 the original author or authors.
+ * Copyright 2010-2013 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.
@@ -48,6 +48,7 @@ public class NoOpCacheManagerTests {
 		Object key = new Object();
 		cache.put(key, new Object());
 		assertNull(cache.get(key));
+		assertNull(cache.get(key, Object.class));
 		assertNull(cache.getNativeCache());
 	}
 

spring-context/src/test/java/org/springframework/cache/concurrent/ConcurrentCacheTests.java

 /*
- * Copyright 2010-2012 the original author or authors.
+ * Copyright 2010-2013 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.
@@ -64,6 +64,9 @@ public class ConcurrentCacheTests  {
 		assertNull(cache.get(key));
 		cache.put(key, value);
 		assertEquals(value, cache.get(key).get());
+		assertEquals(value, cache.get(key, String.class));
+		assertEquals(value, cache.get(key, Object.class));
+		assertEquals(value, cache.get(key, null));
 	}
 
 	@Test