Support for multi-threaded cache access

Previously, if a `@Cacheable` method was accessed with the same key by
multiple threads, the underlying method was invoked several times instead
of blocking the threads while the value is computed. This scenario
typically affects users that enable caching to avoid calling a costly
method too often. When said method can be invoked by an arbitrary number
of clients on startup, caching has close to no effect.

This commit adds a new method on `Cache` that implements the read-through
pattern:

```
<T> T get(Object key, Callable<T> valueLoader);
```

If an entry for a given key is not found, the specified `Callable` is
invoked to "load" the value and cache it before returning it to the
caller. Because the entire operation is managed by the underlying cache
provider, it is much more easier to guarantee that the loader (e.g. the
annotated method) will be called only once in case of concurrent access.

A new `sync` attribute to the `@Cacheable` annotation has been addded.
When this flag is enabled, the caching abstraction invokes the new
`Cache` method define above. This new mode bring a set of limitations:

* It can't be combined with other cache operations
* Only one `@Cacheable` operation can be specified
* Only one cache is allowed
* `condition` and `unless` attribute are not supported

The rationale behind those limitations is that the underlying Cache is
taking care of the actual caching operation so we can't really apply
any SpEL or multiple caches handling there.

Issue: SPR-9254

spring-aspects/src/main/java/org/springframework/cache/aspectj/AbstractCacheAspect.aj

@@ -67,11 +67,22 @@ public abstract aspect AbstractCacheAspect extends CacheAspectSupport implements
 
 		CacheOperationInvoker aspectJInvoker = new CacheOperationInvoker() {
 			public Object invoke() {
-				return proceed(cachedObject);
+				try {
+					return proceed(cachedObject);
+				}
+				catch (Throwable ex) {
+					throw new ThrowableWrapper(ex);
+				}
 			}
 		};
 
-		return execute(aspectJInvoker, thisJoinPoint.getTarget(), method, thisJoinPoint.getArgs());
+		try {
+			return execute(aspectJInvoker, thisJoinPoint.getTarget(), method, thisJoinPoint.getArgs());
+		}
+		catch (CacheOperationInvoker.ThrowableWrapper th) {
+			AnyThrow.throwUnchecked(th.getOriginal());
+			return null; // never reached
+		}
 	}
 
 	/**

spring-aspects/src/main/java/org/springframework/cache/aspectj/AnyThrow.java

@@ -0,0 +1,35 @@
+/*
+ * 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cache.aspectj;
+
+/**
+ * Utility to trick the compiler to throw a valid checked
+ * exceptions within the interceptor.
+ *
+ * @author Stephane Nicoll
+ */
+class AnyThrow {
+
+	static void throwUnchecked(Throwable e) {
+		AnyThrow.<RuntimeException>throwAny(e);
+	}
+
+	@SuppressWarnings("unchecked")
+	private static <E extends Throwable> void throwAny(Throwable e) throws E {
+		throw (E) e;
+	}
+}

spring-aspects/src/main/java/org/springframework/cache/aspectj/JCacheCacheAspect.aj

@@ -109,16 +109,4 @@ public aspect JCacheCacheAspect extends JCacheAspectSupport {
 		execution(@CacheRemoveAll * *(..));
 
 
-	private static class AnyThrow {
-
-		private static void throwUnchecked(Throwable e) {
-			AnyThrow.<RuntimeException>throwAny(e);
-		}
-
-		@SuppressWarnings("unchecked")
-		private static <E extends Throwable> void throwAny(Throwable e) throws E {
-			throw (E)e;
-		}
-	}
-
 }

spring-aspects/src/test/java/org/springframework/cache/config/AnnotatedClassCacheableService.java

@@ -27,6 +27,7 @@ import org.springframework.cache.annotation.Caching;
 /**
  * @author Costin Leau
  * @author Phillip Webb
+ * @author Stephane Nicoll
  */
 @Cacheable("testCache")
 public class AnnotatedClassCacheableService implements CacheableService<Object> {
@@ -44,11 +45,28 @@ public class AnnotatedClassCacheableService implements CacheableService<Object>
 		return null;
 	}
 
+	@Override
+	@Cacheable(cacheNames = "testCache", sync = true)
+	public Object cacheSync(Object arg1) {
+		return counter.getAndIncrement();
+	}
+
+	@Override
+	@Cacheable(cacheNames = "testCache", sync = true)
+	public Object cacheSyncNull(Object arg1) {
+		return null;
+	}
+
 	@Override
 	public Object conditional(int field) {
 		return null;
 	}
 
+	@Override
+	public Object conditionalSync(int field) {
+		return null;
+	}
+
 	@Override
 	public Object unless(int arg) {
 		return arg;
@@ -168,6 +186,18 @@ public class AnnotatedClassCacheableService implements CacheableService<Object>
 		throw new UnsupportedOperationException(arg1.toString());
 	}
 
+	@Override
+	@Cacheable(cacheNames = "testCache", sync = true)
+	public Object throwCheckedSync(Object arg1) throws Exception {
+		throw new IOException(arg1.toString());
+	}
+
+	@Override
+	@Cacheable(cacheNames = "testCache", sync = true)
+	public Object throwUncheckedSync(Object arg1) {
+		throw new UnsupportedOperationException(arg1.toString());
+	}
+
 	// multi annotations
 
 	@Override

spring-aspects/src/test/java/org/springframework/cache/config/CacheableService.java

@@ -21,6 +21,7 @@ package org.springframework.cache.config;
  *
  * @author Costin Leau
  * @author Phillip Webb
+ * @author Stephane Nicoll
  */
 public interface CacheableService<T> {
 
@@ -28,6 +29,10 @@ public interface CacheableService<T> {
 
 	T cacheNull(Object arg1);
 
+	T cacheSync(Object arg1);
+
+	T cacheSyncNull(Object arg1);
+
 	void invalidate(Object arg1);
 
 	void evictEarly(Object arg1);
@@ -42,6 +47,8 @@ public interface CacheableService<T> {
 
 	T conditional(int field);
 
+	T conditionalSync(int field);
+
 	T unless(int arg);
 
 	T key(Object arg1, Object arg2);
@@ -72,6 +79,10 @@ public interface CacheableService<T> {
 
 	T throwUnchecked(Object arg1);
 
+	T throwCheckedSync(Object arg1) throws Exception;
+
+	T throwUncheckedSync(Object arg1);
+
 	// multi annotations
 	T multiCache(Object arg1);
 

spring-aspects/src/test/java/org/springframework/cache/config/DefaultCacheableService.java

@@ -29,6 +29,7 @@ import org.springframework.cache.annotation.Caching;
  *
  * @author Costin Leau
  * @author Phillip Webb
+ * @author Stephane Nicoll
  */
 public class DefaultCacheableService implements CacheableService<Long> {
 
@@ -47,6 +48,18 @@ public class DefaultCacheableService implements CacheableService<Long> {
 		return null;
 	}
 
+	@Override
+	@Cacheable(cacheNames = "testCache", sync = true)
+	public Long cacheSync(Object arg1) {
+		return counter.getAndIncrement();
+	}
+
+	@Override
+	@Cacheable(cacheNames = "testCache", sync = true)
+	public Long cacheSyncNull(Object arg1) {
+		return null;
+	}
+
 	@Override
 	@CacheEvict("testCache")
 	public void invalidate(Object arg1) {
@@ -81,11 +94,17 @@ public class DefaultCacheableService implements CacheableService<Long> {
 	}
 
 	@Override
-	@Cacheable(cacheNames = "testCache", condition = "#classField == 3")
+	@Cacheable(cacheNames = "testCache", condition = "#p0 == 3")
 	public Long conditional(int classField) {
 		return counter.getAndIncrement();
 	}
 
+	@Override
+	@Cacheable(cacheNames = "testCache", sync = true, condition = "#p0 == 3")
+	public Long conditionalSync(int field) {
+		return counter.getAndIncrement();
+	}
+
 	@Override
 	@Cacheable(cacheNames = "testCache", unless = "#result > 10")
 	public Long unless(int arg) {
@@ -99,7 +118,7 @@ public class DefaultCacheableService implements CacheableService<Long> {
 	}
 
 	@Override
-	@Cacheable("testCache")
+	@Cacheable(cacheNames = "testCache")
 	public Long varArgsKey(Object... args) {
 		return counter.getAndIncrement();
 	}
@@ -176,6 +195,18 @@ public class DefaultCacheableService implements CacheableService<Long> {
 		throw new UnsupportedOperationException(arg1.toString());
 	}
 
+	@Override
+	@Cacheable(cacheNames = "testCache", sync = true)
+	public Long throwCheckedSync(Object arg1) throws Exception {
+		throw new IOException(arg1.toString());
+	}
+
+	@Override
+	@Cacheable(cacheNames = "testCache", sync = true)
+	public Long throwUncheckedSync(Object arg1) {
+		throw new UnsupportedOperationException(arg1.toString());
+	}
+
 	// multi annotations
 
 	@Override

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

@@ -16,6 +16,7 @@
 
 package org.springframework.cache.caffeine;
 
+import java.util.concurrent.Callable;
 import java.util.function.Function;
 
 import com.github.benmanes.caffeine.cache.LoadingCache;
@@ -88,6 +89,12 @@ public class CaffeineCache extends AbstractValueAdaptingCache {
 		return super.get(key);
 	}
 
+	@SuppressWarnings("unchecked")
+	@Override
+	public <T> T get(Object key, final Callable<T> valueLoader) {
+		return (T) fromStoreValue(this.cache.get(key, new LoadFunction(valueLoader)));
+	}
+
 	@Override
 	protected Object lookup(Object key) {
 		return this.cache.getIfPresent(key);
@@ -133,4 +140,23 @@ public class CaffeineCache extends AbstractValueAdaptingCache {
 		}
 	}
 
+	private class LoadFunction implements Function<Object, Object> {
+
+		private final Callable<?> valueLoader;
+
+		public LoadFunction(Callable<?> valueLoader) {
+			this.valueLoader = valueLoader;
+		}
+
+		@Override
+		public Object apply(Object o) {
+			try {
+				return toStoreValue(valueLoader.call());
+			}
+			catch (Exception ex) {
+				throw new ValueRetrievalException(o, valueLoader, ex);
+			}
+		}
+	}
+
 }

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

@@ -16,6 +16,8 @@
 
 package org.springframework.cache.ehcache;
 
+import java.util.concurrent.Callable;
+
 import net.sf.ehcache.Ehcache;
 import net.sf.ehcache.Element;
 import net.sf.ehcache.Status;
@@ -62,10 +64,47 @@ public class EhCacheCache implements Cache {
 
 	@Override
 	public ValueWrapper get(Object key) {
-		Element element = this.cache.get(key);
+		Element element = lookup(key);
 		return toValueWrapper(element);
 	}
 
+	@SuppressWarnings("unchecked")
+	@Override
+	public <T> T get(Object key, Callable<T> valueLoader) {
+		Element element = lookup(key);
+		if (element != null) {
+			return (T) element.getObjectValue();
+		}
+		else {
+			this.cache.acquireWriteLockOnKey(key);
+			try {
+				element = lookup(key); // One more attempt with the write lock
+				if (element != null) {
+					return (T) element.getObjectValue();
+				}
+				else {
+					return loadValue(key, valueLoader);
+				}
+			}
+			finally {
+				this.cache.releaseWriteLockOnKey(key);
+			}
+		}
+
+	}
+
+	private <T> T loadValue(Object key, Callable<T> valueLoader) {
+		T value;
+		try {
+			value = valueLoader.call();
+		}
+		catch (Exception ex) {
+			throw new ValueRetrievalException(key, valueLoader, ex);
+		}
+		put(key, value);
+		return value;
+	}
+
 	@Override
 	@SuppressWarnings("unchecked")
 	public <T> T get(Object key, Class<T> type) {
@@ -98,6 +137,11 @@ public class EhCacheCache implements Cache {
 		this.cache.removeAll();
 	}
 
+
+	private Element lookup(Object key) {
+		return this.cache.get(key);
+	}
+
 	private ValueWrapper toValueWrapper(Element element) {
 		return (element != null ? new SimpleValueWrapper(element.getObjectValue()) : null);
 	}

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

@@ -93,6 +93,25 @@ public class GuavaCache extends AbstractValueAdaptingCache {
 		return super.get(key);
 	}
 
+	@SuppressWarnings("unchecked")
+	@Override
+	public <T> T get(Object key, final Callable<T> valueLoader) {
+		try {
+			return (T) fromStoreValue(this.cache.get(key, new Callable<Object>() {
+				@Override
+				public Object call() throws Exception {
+					return toStoreValue(valueLoader.call());
+				}
+			}));
+		}
+		catch (ExecutionException ex) {
+			throw new ValueRetrievalException(key, valueLoader, ex.getCause());
+		}
+		catch (UncheckedExecutionException ex) {
+			throw new ValueRetrievalException(key, valueLoader, ex.getCause());
+		}
+	}
+
 	@Override
 	protected Object lookup(Object key) {
 		return this.cache.getIfPresent(key);

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

@@ -16,6 +16,11 @@
 
 package org.springframework.cache.jcache;
 
+import java.util.concurrent.Callable;
+import javax.cache.processor.EntryProcessor;
+import javax.cache.processor.EntryProcessorException;
+import javax.cache.processor.MutableEntry;
+
 import org.springframework.cache.support.AbstractValueAdaptingCache;
 import org.springframework.util.Assert;
 
@@ -69,6 +74,16 @@ public class JCacheCache extends AbstractValueAdaptingCache {
 		return this.cache.get(key);
 	}
 
+	@Override
+	public <T> T get(Object key, Callable<T> valueLoader) {
+		try {
+			return this.cache.invoke(key, new ValueLoaderEntryProcessor<T>(), valueLoader);
+		}
+		catch (EntryProcessorException ex) {
+			throw new ValueRetrievalException(key, valueLoader, ex.getCause());
+		}
+	}
+
 	@Override
 	public void put(Object key, Object value) {
 		this.cache.put(key, toStoreValue(value));
@@ -90,4 +105,30 @@ public class JCacheCache extends AbstractValueAdaptingCache {
 		this.cache.removeAll();
 	}
 
+
+	private class ValueLoaderEntryProcessor<T> implements EntryProcessor<Object, Object, T> {
+
+		@SuppressWarnings("unchecked")
+		@Override
+		public T process(MutableEntry<Object, Object> entry, Object... arguments)
+				throws EntryProcessorException {
+			Callable<T> valueLoader = (Callable<T>) arguments[0];
+			if (entry.exists()) {
+				return (T) fromStoreValue(entry.getValue());
+			}
+			else {
+				T value;
+				try {
+					value = valueLoader.call();
+				}
+				catch (Exception ex) {
+					throw new EntryProcessorException("Value loader '" + valueLoader + "' failed " +
+							"to compute  value for key '" + entry.getKey() + "'", ex);
+				}
+				entry.setValue(toStoreValue(value));
+				return value;
+			}
+		}
+	}
+
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 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.
@@ -16,6 +16,8 @@
 
 package org.springframework.cache.transaction;
 
+import java.util.concurrent.Callable;
+
 import org.springframework.cache.Cache;
 import org.springframework.transaction.support.TransactionSynchronizationAdapter;
 import org.springframework.transaction.support.TransactionSynchronizationManager;
@@ -72,6 +74,11 @@ public class TransactionAwareCacheDecorator implements Cache {
 		return this.targetCache.get(key, type);
 	}
 
+	@Override
+	public <T> T get(Object key, Callable<T> valueLoader) {
+		return this.targetCache.get(key, valueLoader);
+	}
+
 	@Override
 	public void put(final Object key, final Object value) {
 		if (TransactionSynchronizationManager.isSynchronizationActive()) {

spring-context-support/src/test/java/org/springframework/cache/caffeine/CaffeineCacheTests.java

@@ -52,7 +52,7 @@ public class CaffeineCacheTests extends AbstractCacheTests<CaffeineCache> {
 	}
 
 	@Test
-	public void putIfAbsentNullValue() throws Exception {
+	public void testPutIfAbsentNullValue() throws Exception {
 		CaffeineCache cache = getCache();
 
 		Object key = new Object();
@@ -66,4 +66,5 @@ public class CaffeineCacheTests extends AbstractCacheTests<CaffeineCache> {
 		assertEquals(null, wrapper.get());
 		assertEquals(value, cache.get(key).get()); // not changed
 	}
+
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2014 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.
@@ -82,4 +82,5 @@ public class EhCacheCacheTests extends AbstractCacheTests<EhCacheCache> {
 		Thread.sleep(5 * 1000);
 		assertNull(cache.get(key));
 	}
+
 }

spring-context-support/src/test/java/org/springframework/cache/guava/GuavaCacheTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 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.
@@ -64,4 +64,5 @@ public class GuavaCacheTests extends AbstractCacheTests<GuavaCache> {
 		assertEquals(null, wrapper.get());
 		assertEquals(value, cache.get(key).get()); // not changed
 	}
+
 }

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

@@ -16,6 +16,8 @@
 
 package org.springframework.cache;
 
+import java.util.concurrent.Callable;
+
 /**
  * Interface that defines common cache operations.
  *
@@ -73,6 +75,23 @@ public interface Cache {
 	 */
 	<T> T get(Object key, Class<T> type);
 
+	/**
+	 * Return the value to which this cache maps the specified key, obtaining
+	 * that value from {@code valueLoader} if necessary. This method provides
+	 * a simple substitute for the conventional "if cached, return; otherwise
+	 * create, cache and return" pattern.
+	 * <p>If possible, implementations should ensure that the loading operation
+	 * is synchronized so that the specified {@code valueLoader} is only called
+	 * once in case of concurrent access on the same key.
+	 * <p>If the {@code valueLoader} throws an exception, it is wrapped in
+	 * a {@link ValueRetrievalException}
+	 * @param key the key whose associated value is to be returned
+	 * @return the value to which this cache maps the specified key
+	 * @throws ValueRetrievalException if the {@code valueLoader} throws an exception
+	 * @since 4.3
+	 */
+	<T> T get(Object key, Callable<T> valueLoader);
+
 	/**
 	 * Associate the specified value with the specified key in this cache.
 	 * <p>If the cache previously contained a mapping for this key, the old
@@ -133,4 +152,24 @@ public interface Cache {
 		Object get();
 	}
 
+	/**
+	 * TODO
+	 */
+	@SuppressWarnings("serial")
+	class ValueRetrievalException extends RuntimeException {
+
+		private final Object key;
+
+		public ValueRetrievalException(Object key, Callable<?> loader, Throwable ex) {
+			super(String.format("Value for key '%s' could not " +
+					"be loaded using '%s'", key, loader), ex);
+			this.key = key;
+		}
+
+		public Object getKey() {
+			return key;
+		}
+
+	}
+
 }

spring-context/src/main/java/org/springframework/cache/annotation/Cacheable.java

@@ -22,6 +22,7 @@ import java.lang.annotation.Inherited;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
+import java.util.concurrent.Callable;
 
 import org.springframework.core.annotation.AliasFor;
 
@@ -154,4 +155,21 @@ public @interface Cacheable {
 	 */
 	String unless() default "";
 
+	/**
+	 * Synchronize the invocation of the underlying method if several threads are
+	 * attempting to load a value for the same key. The synchronization leads to
+	 * a couple of limitations:
+	 * <ol>
+	 * <li>{@link #unless()} is not supported</li>
+	 * <li>Only one cache may be specified</li>
+	 * <li>No other cache-related operation can be combined</li>
+	 * </ol>
+	 * This is effectively a hint and the actual cache provider that you are
+	 * using may not support it in a synchronized fashion. Check your provider
+	 * documentation for more details on the actual semantics.
+	 * @since 4.3
+	 * @see org.springframework.cache.Cache#get(Object, Callable)
+	 */
+	boolean sync() default false;
+
 }

spring-context/src/main/java/org/springframework/cache/annotation/SpringCacheAnnotationParser.java

@@ -107,6 +107,7 @@ public class SpringCacheAnnotationParser implements CacheAnnotationParser, Seria
 		op.setKeyGenerator(cacheable.keyGenerator());
 		op.setCacheManager(cacheable.cacheManager());
 		op.setCacheResolver(cacheable.cacheResolver());
+		op.setSync(cacheable.sync());
 		op.setName(ae.toString());
 
 		defaultConfig.applyDefault(op);

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

@@ -16,6 +16,7 @@
 
 package org.springframework.cache.concurrent;
 
+import java.util.concurrent.Callable;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
 
@@ -96,6 +97,30 @@ public class ConcurrentMapCache extends AbstractValueAdaptingCache {
 		return this.store.get(key);
 	}
 
+	@SuppressWarnings("unchecked")
+	@Override
+	public <T> T get(Object key, Callable<T> valueLoader) {
+		if (this.store.containsKey(key)) {
+			return (T) get(key).get();
+		}
+		else {
+			synchronized (this.store) {
+				if (this.store.containsKey(key)) {
+					return (T) get(key).get();
+				}
+				T value;
+				try {
+					value = valueLoader.call();
+				}
+				catch (Exception ex) {
+					throw new ValueRetrievalException(key, valueLoader, ex);
+				}
+				put(key, value);
+				return value;
+			}
+		}
+	}
+
 	@Override
 	public void put(Object key, Object value) {
 		this.store.put(key, toStoreValue(value));

spring-context/src/main/java/org/springframework/cache/config/CacheAdviceParser.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 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.
@@ -109,6 +109,7 @@ class CacheAdviceParser extends AbstractSingleBeanDefinitionParser {
 			nameHolder.setSource(parserContext.extractSource(opElement));
 			CacheableOperation op = prop.merge(opElement, parserContext.getReaderContext(), new CacheableOperation());
 			op.setUnless(getAttributeValue(opElement, "unless", ""));
+			op.setSync(Boolean.valueOf(getAttributeValue(opElement, "sync", "false")));
 
 			Collection<CacheOperation> col = cacheOpMap.get(nameHolder);
 			if (col == null) {

spring-context/src/main/java/org/springframework/cache/interceptor/CacheAspectSupport.java

@@ -23,6 +23,7 @@ import java.util.Collections;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.Callable;
 import java.util.concurrent.ConcurrentHashMap;
 
 import org.apache.commons.logging.Log;
@@ -328,7 +329,34 @@ public abstract class CacheAspectSupport extends AbstractCacheInvoker
 		return targetClass;
 	}
 
-	private Object execute(CacheOperationInvoker invoker, CacheOperationContexts contexts) {
+	private Object execute(final CacheOperationInvoker invoker, CacheOperationContexts contexts) {
+		// Special handling of synchronized invocation
+		if (contexts.isSynchronized()) {
+			CacheOperationContext context = contexts.get(CacheableOperation.class).iterator().next();
+			if (isConditionPassing(context, ExpressionEvaluator.NO_RESULT)) {
+				Object key = generateKey(context, ExpressionEvaluator.NO_RESULT);
+				Cache cache = context.getCaches().iterator().next();
+				try {
+					return cache.get(key, new Callable<Object>() {
+						@Override
+						public Object call() throws Exception {
+							return invokeOperation(invoker);
+						}
+					});
+				}
+				catch (Cache.ValueRetrievalException ex) {
+					// The invoker wraps any Throwable in a ThrowableWrapper instance so we
+					// can just make sure that one bubbles up the stack.
+					throw (CacheOperationInvoker.ThrowableWrapper) ex.getCause();
+				}
+			}
+			else {
+				// No caching required, only call the underlying method
+				return invokeOperation(invoker);
+			}
+		}
+
+
 		// Process any early evictions
 		processCacheEvicts(contexts.get(CacheEvictOperation.class), true, ExpressionEvaluator.NO_RESULT);
 
@@ -374,7 +402,7 @@ public abstract class CacheAspectSupport extends AbstractCacheInvoker
 		for (CacheOperationContext context : cachePutContexts) {
 			try {
 				if (!context.isConditionPassing(ExpressionEvaluator.RESULT_UNAVAILABLE)) {
-	                excluded.add(context);
+					excluded.add(context);
 				}
 			}
 			catch (VariableNotAvailableException e) {
@@ -385,7 +413,6 @@ public abstract class CacheAspectSupport extends AbstractCacheInvoker
 		// check if  all puts have been excluded by condition
 		return cachePutContexts.size() != excluded.size();
 
-
 	}
 
 	private void processCacheEvicts(Collection<CacheOperationContext> contexts, boolean beforeInvocation, Object result) {
@@ -504,18 +531,57 @@ public abstract class CacheAspectSupport extends AbstractCacheInvoker
 		private final MultiValueMap<Class<? extends CacheOperation>, CacheOperationContext> contexts =
 				new LinkedMultiValueMap<Class<? extends CacheOperation>, CacheOperationContext>();
 
+		private final boolean sync;
+
 		public CacheOperationContexts(Collection<? extends CacheOperation> operations, Method method,
 				Object[] args, Object target, Class<?> targetClass) {
 
 			for (CacheOperation operation : operations) {
 				this.contexts.add(operation.getClass(), getOperationContext(operation, method, args, target, targetClass));
 			}
+			this.sync = determineSyncFlag(method);
 		}
 
 		public Collection<CacheOperationContext> get(Class<? extends CacheOperation> operationClass) {
 			Collection<CacheOperationContext> result = this.contexts.get(operationClass);
 			return (result != null ? result : Collections.<CacheOperationContext>emptyList());
 		}
+
+		public boolean isSynchronized() {
+			return this.sync;
+		}
+
+		private boolean determineSyncFlag(Method method) {
+			List<CacheOperationContext> cacheOperationContexts = this.contexts.get(CacheableOperation.class);
+			if (cacheOperationContexts == null) { // No @Cacheable operation
+				return false;
+			}
+			boolean syncEnabled = false;
+			for (CacheOperationContext cacheOperationContext : cacheOperationContexts) {
+				if (((CacheableOperation) cacheOperationContext.getOperation()).isSync()) {
+					syncEnabled = true;
+					break;
+				}
+			}
+			if (syncEnabled) {
+				if (this.contexts.size() > 1) {
+					throw new IllegalStateException("@Cacheable(sync = true) cannot be combined with other cache operations on '" + method + "'");
+				}
+				if (cacheOperationContexts.size() > 1) {
+					throw new IllegalStateException("Only one @Cacheable(sync = true) entry is allowed on '" + method + "'");
+				}
+				CacheOperationContext cacheOperationContext = cacheOperationContexts.iterator().next();
+				CacheableOperation operation = (CacheableOperation) cacheOperationContext.getOperation();
+				if (cacheOperationContext.getCaches().size() > 1) {
+					throw new IllegalStateException("@Cacheable(sync = true) only allows a single cache on '" + operation + "'");
+				}
+				if (StringUtils.hasText(operation.getUnless())) {
+					throw new IllegalStateException("@Cacheable(sync = true) does not support unless attribute on '" + operation + "'");
+				}
+				return true;
+			}
+			return false;
+		}
 	}
 
 

spring-context/src/main/java/org/springframework/cache/interceptor/CacheOperationInvoker.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 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.
@@ -42,7 +42,7 @@ public interface CacheOperationInvoker {
 	 * Wrap any exception thrown while invoking {@link #invoke()}
 	 */
 	@SuppressWarnings("serial")
-	public static class ThrowableWrapper extends RuntimeException {
+	class ThrowableWrapper extends RuntimeException {
 
 		private final Throwable original;
 

spring-context/src/main/java/org/springframework/cache/interceptor/CacheableOperation.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2013 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.
@@ -27,6 +27,8 @@ public class CacheableOperation extends CacheOperation {
 
 	private String unless;
 
+	private boolean sync;
+
 
 	public String getUnless() {
 		return unless;
@@ -36,12 +38,23 @@ public class CacheableOperation extends CacheOperation {
 		this.unless = unless;
 	}
 
+	public boolean isSync() {
+		return sync;
+	}
+
+	public void setSync(boolean sync) {
+		this.sync = sync;
+	}
+
 	@Override
 	protected StringBuilder getOperationDescription() {
 		StringBuilder sb = super.getOperationDescription();
 		sb.append(" | unless='");
 		sb.append(this.unless);
 		sb.append("'");
+		sb.append(" | sync='");
+		sb.append(this.sync);
+		sb.append("'");
 		return sb;
 	}
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 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.
@@ -20,6 +20,7 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.LinkedHashSet;
 import java.util.Set;
+import java.util.concurrent.Callable;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
 
@@ -99,6 +100,11 @@ public class NoOpCacheManager implements CacheManager {
 			return null;
 		}
 
+		@Override
+		public <T> T get(Object key, Callable<T> valueLoader) {
+			return null;
+		}
+
 		@Override
 		public String getName() {
 			return this.name;

spring-context/src/main/resources/org/springframework/cache/config/spring-cache-4.3.xsd

@@ -261,6 +261,13 @@
 	The SpEL expression used to veto the method caching.]]></xsd:documentation>
 										</xsd:annotation>
 									</xsd:attribute>
+									<xsd:attribute name="sync" type="xsd:boolean" use="optional" default="false">
+										<xsd:annotation>
+											<xsd:documentation><![CDATA[
+	Synchronize the invocation of the underlying method if several threads
+	are attempting to load a value for the same key]]></xsd:documentation>
+										</xsd:annotation>
+									</xsd:attribute>
 								</xsd:extension>
 							</xsd:complexContent>
 						</xsd:complexType>

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

@@ -16,10 +16,17 @@
 
 package org.springframework.cache;
 
+import java.util.List;
+import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.atomic.AtomicInteger;
 import java.util.UUID;
 
+import org.junit.Rule;
 import org.junit.Test;
+import org.junit.rules.ExpectedException;
 
+import static org.hamcrest.core.Is.*;
 import static org.junit.Assert.*;
 
 /**
@@ -27,6 +34,9 @@ import static org.junit.Assert.*;
  */
 public abstract class AbstractCacheTests<T extends Cache> {
 
+	@Rule
+	public final ExpectedException thrown = ExpectedException.none();
+
 	protected final static String CACHE_NAME = "testCache";
 
 	protected abstract T getCache();
@@ -59,7 +69,7 @@ public abstract class AbstractCacheTests<T extends Cache> {
 		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));
+		assertEquals(value, cache.get(key, (Class<?>) null));
 
 		cache.put(key, null);
 		assertNotNull(cache.get(key));
@@ -106,6 +116,100 @@ public abstract class AbstractCacheTests<T extends Cache> {
 		assertNull(cache.get("enescu"));
 	}
 
+	@Test
+	public void testCacheGetCallable() {
+		doTestCacheGetCallable("test");
+	}
+
+	@Test
+	public void testCacheGetCallableWithNull() {
+		doTestCacheGetCallable(null);
+	}
+
+	private void doTestCacheGetCallable(Object returnValue) {
+		T cache = getCache();
+
+		String key = createRandomKey();
+
+		assertNull(cache.get(key));
+		Object value = cache.get(key, () -> returnValue );
+		assertEquals(returnValue, value);
+		assertEquals(value, cache.get(key).get());
+	}
+
+	@Test
+	public void testCacheGetCallableNotInvokedWithHit() {
+		doTestCacheGetCallableNotInvokedWithHit("existing");
+	}
+
+	@Test
+	public void testCacheGetCallableNotInvokedWithHitNull() {
+		doTestCacheGetCallableNotInvokedWithHit(null);
+	}
+
+	private void doTestCacheGetCallableNotInvokedWithHit(Object initialValue) {
+		T cache = getCache();
+
+		String key = createRandomKey();
+		cache.put(key, initialValue);
+
+		Object value = cache.get(key, () -> {
+			throw new IllegalStateException("Should not have been invoked");
+		});
+		assertEquals(initialValue, value);
+	}
+
+	@Test
+	public void testCacheGetCallableFail() {
+		T cache = getCache();
+
+		String key = createRandomKey();
+		assertNull(cache.get(key));
+
+		try {
+			cache.get(key, () -> {
+				throw new UnsupportedOperationException("Expected exception");
+			});
+		}
+		catch (Cache.ValueRetrievalException ex) {
+			assertNotNull(ex.getCause());
+			assertEquals(UnsupportedOperationException.class, ex.getCause().getClass());
+		}
+	}
+
+	/**
+	 * Test that a call to get with a Callable concurrently properly synchronize the
+	 * invocations.
+	 */
+	@Test
+	public void testCacheGetSynchronized() throws InterruptedException {
+		T cache = getCache();
+		final AtomicInteger counter = new AtomicInteger();
+		final List<Object> results = new CopyOnWriteArrayList<>();
+		final CountDownLatch latch = new CountDownLatch(10);
+
+		String key = createRandomKey();
+		Runnable run = () -> {
+			try {
+				Integer value = cache.get(key, () -> {
+					Thread.sleep(50); // make sure the thread will overlap
+					return counter.incrementAndGet();
+				});
+				results.add(value);
+			}
+			finally {
+				latch.countDown();
+			}
+		};
+
+		for (int i = 0; i < 10; i++) {
+			new Thread(run).start();
+		}
+		latch.await();
+
+		assertEquals(10, results.size());
+		results.forEach(r -> assertThat(r, is(1))); // Only one method got invoked
+	}
 
 	private String createRandomKey() {
 		return UUID.randomUUID().toString();

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

@@ -1,115 +0,0 @@
-/*
- * Copyright 2002-2014 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.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.springframework.cache.concurrent;
-
-import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.ConcurrentMap;
-
-import org.junit.Before;
-import org.junit.Test;
-
-import org.springframework.cache.Cache;
-
-import static org.junit.Assert.*;
-
-/**
- * @author Costin Leau
- * @author Juergen Hoeller
- * @author Stephane Nicoll
- */
-public class ConcurrentCacheTests  {
-
-	protected final static String CACHE_NAME = "testCache";
-
-	protected ConcurrentMap<Object, Object> nativeCache;
-
-	protected Cache cache;
-
-
-	@Before
-	public void setUp() throws Exception {
-		nativeCache = new ConcurrentHashMap<Object, Object>();
-		cache = new ConcurrentMapCache(CACHE_NAME, nativeCache, true);
-		cache.clear();
-	}
-
-
-	@Test
-	public void testCacheName() throws Exception {
-		assertEquals(CACHE_NAME, cache.getName());
-	}
-
-	@Test
-	public void testNativeCache() throws Exception {
-		assertSame(nativeCache, cache.getNativeCache());
-	}
-
-	@Test
-	public void testCachePut() throws Exception {
-		Object key = "enescu";
-		Object value = "george";
-
-		assertNull(cache.get(key));
-		assertNull(cache.get(key, String.class));
-		assertNull(cache.get(key, Object.class));
-
-		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));
-
-		cache.put(key, null);
-		assertNotNull(cache.get(key));
-		assertNull(cache.get(key).get());
-		assertNull(cache.get(key, String.class));
-		assertNull(cache.get(key, Object.class));
-	}
-
-	@Test
-	public void testCachePutIfAbsent() throws Exception {
-		Object key = new Object();
-		Object value = "initialValue";
-
-		assertNull(cache.get(key));
-		assertNull(cache.putIfAbsent(key, value));
-		assertEquals(value, cache.get(key).get());
-		assertEquals("initialValue", cache.putIfAbsent(key, "anotherValue").get());
-		assertEquals(value, cache.get(key).get()); // not changed
-	}
-
-	@Test
-	public void testCacheRemove() throws Exception {
-		Object key = "enescu";
-		Object value = "george";
-
-		assertNull(cache.get(key));
-		cache.put(key, value);
-	}
-
-	@Test
-	public void testCacheClear() throws Exception {
-		assertNull(cache.get("enescu"));
-		cache.put("enescu", "george");
-		assertNull(cache.get("vlaicu"));
-		cache.put("vlaicu", "aurel");
-		cache.clear();
-		assertNull(cache.get("vlaicu"));
-		assertNull(cache.get("enescu"));
-	}
-
-}

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

@@ -0,0 +1,56 @@
+/*
+ * 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cache.concurrent;
+
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+
+import org.junit.Before;
+import org.junit.Ignore;
+
+import org.springframework.cache.AbstractCacheTests;
+
+/**
+ * @author Costin Leau
+ * @author Juergen Hoeller
+ * @author Stephane Nicoll
+ */
+public class ConcurrentMapCacheTests extends AbstractCacheTests<ConcurrentMapCache> {
+
+	protected ConcurrentMap<Object, Object> nativeCache;
+
+	protected ConcurrentMapCache cache;
+
+
+	@Before
+	public void setUp() throws Exception {
+		nativeCache = new ConcurrentHashMap<Object, Object>();
+		cache = new ConcurrentMapCache(CACHE_NAME, nativeCache, true);
+		cache.clear();
+	}
+
+	@Override
+	protected ConcurrentMapCache getCache() {
+		return this.cache;
+	}
+
+	@Override
+	protected ConcurrentMap<Object, Object> getNativeCache() {
+		return this.nativeCache;
+	}
+
+}

spring-context/src/test/java/org/springframework/cache/config/AbstractCacheAnnotationTests.java

@@ -105,6 +105,32 @@ public abstract class AbstractCacheAnnotationTests {
 		assertNull("Cached value should be null", r3);
 	}
 
+	public void testCacheableSync(CacheableService<?> service) throws Exception {
+		Object o1 = new Object();
+
+		Object r1 = service.cacheSync(o1);
+		Object r2 = service.cacheSync(o1);
+		Object r3 = service.cacheSync(o1);
+
+		assertSame(r1, r2);
+		assertSame(r1, r3);
+	}
+
+	public void testCacheableSyncNull(CacheableService<?> service) throws Exception {
+		Object o1 = new Object();
+		assertNull(cm.getCache("testCache").get(o1));
+
+		Object r1 = service.cacheSyncNull(o1);
+		Object r2 = service.cacheSyncNull(o1);
+		Object r3 = service.cacheSyncNull(o1);
+
+		assertSame(r1, r2);
+		assertSame(r1, r3);
+
+		assertEquals(r3, cm.getCache("testCache").get(o1).get());
+		assertNull("Cached value should be null", r3);
+	}
+
 	public void testEvict(CacheableService<?> service) throws Exception {
 		Object o1 = new Object();
 
@@ -225,6 +251,18 @@ public abstract class AbstractCacheAnnotationTests {
 		assertSame(r3, r4);
 	}
 
+	public void testConditionalExpressionSync(CacheableService<?> service) throws Exception {
+		Object r1 = service.conditionalSync(4);
+		Object r2 = service.conditionalSync(4);
+
+		assertNotSame(r1, r2);
+
+		Object r3 = service.conditionalSync(3);
+		Object r4 = service.conditionalSync(3);
+
+		assertSame(r3, r4);
+	}
+
 	public void testUnlessExpression(CacheableService<?> service) throws Exception {
 		Cache cache = cm.getCache("testCache");
 		cache.clear();
@@ -311,6 +349,28 @@ public abstract class AbstractCacheAnnotationTests {
 		}
 	}
 
+	public void testCheckedThrowableSync(CacheableService<?> service) throws Exception {
+		String arg = UUID.randomUUID().toString();
+		try {
+			service.throwCheckedSync(arg);
+			fail("Excepted exception");
+		} catch (Exception ex) {
+			ex.printStackTrace();
+			assertEquals("Wrong exception type", IOException.class, ex.getClass());
+			assertEquals(arg, ex.getMessage());
+		}
+	}
+
+	public void testUncheckedThrowableSync(CacheableService<?> service) throws Exception {
+		try {
+			service.throwUncheckedSync(Long.valueOf(1));
+			fail("Excepted exception");
+		} catch (RuntimeException ex) {
+			assertEquals("Wrong exception type", UnsupportedOperationException.class, ex.getClass());
+			assertEquals("1", ex.getMessage());
+		}
+	}
+
 	public void testNullArg(CacheableService<?> service) {
 		Object r1 = service.cache(null);
 		assertSame(r1, service.cache(null));
@@ -483,6 +543,16 @@ public abstract class AbstractCacheAnnotationTests {
 		testCacheableNull(cs);
 	}
 
+	@Test
+	public void testCacheableSync() throws Exception {
+		testCacheableSync(cs);
+	}
+
+	@Test
+	public void testCacheableSyncNull() throws Exception {
+		testCacheableSyncNull(cs);
+	}
+
 	@Test
 	public void testInvalidate() throws Exception {
 		testEvict(cs);
@@ -518,6 +588,11 @@ public abstract class AbstractCacheAnnotationTests {
 		testConditionalExpression(cs);
 	}
 
+	@Test
+	public void testConditionalExpressionSync() throws Exception {
+		testConditionalExpressionSync(cs);
+	}
+
 	@Test
 	public void testUnlessExpression() throws Exception {
 		testUnlessExpression(cs);
@@ -677,6 +752,16 @@ public abstract class AbstractCacheAnnotationTests {
 		testCheckedThrowable(ccs);
 	}
 
+	@Test
+	public void testCheckedExceptionSync() throws Exception {
+		testCheckedThrowableSync(cs);
+	}
+
+	@Test
+	public void testClassCheckedExceptionSync() throws Exception {
+		testCheckedThrowableSync(ccs);
+	}
+
 	@Test
 	public void testUncheckedException() throws Exception {
 		testUncheckedThrowable(cs);
@@ -687,6 +772,16 @@ public abstract class AbstractCacheAnnotationTests {
 		testUncheckedThrowable(ccs);
 	}
 
+	@Test
+	public void testUncheckedExceptionSync() throws Exception {
+		testUncheckedThrowableSync(cs);
+	}
+
+	@Test
+	public void testClassUncheckedExceptionSync() throws Exception {
+		testUncheckedThrowableSync(ccs);
+	}
+
 	@Test
 	public void testUpdate() {
 		testCacheUpdate(cs);

spring-context/src/test/java/org/springframework/cache/config/AnnotatedClassCacheableService.java

@@ -46,11 +46,28 @@ public class AnnotatedClassCacheableService implements CacheableService<Object>
 		return null;
 	}
 
+	@Override
+	@Cacheable(cacheNames = "testCache", sync = true)
+	public Object cacheSync(Object arg1) {
+		return counter.getAndIncrement();
+	}
+
+	@Override
+	@Cacheable(cacheNames = "testCache", sync = true)
+	public Object cacheSyncNull(Object arg1) {
+		return null;
+	}
+
 	@Override
 	public Object conditional(int field) {
 		return null;
 	}
 
+	@Override
+	public Object conditionalSync(int field) {
+		return null;
+	}
+
 	@Override
 	@Cacheable(cacheNames = "testCache", unless = "#result > 10")
 	public Object unless(int arg) {
@@ -171,6 +188,18 @@ public class AnnotatedClassCacheableService implements CacheableService<Object>
 		throw new UnsupportedOperationException(arg1.toString());
 	}
 
+	@Override
+	@Cacheable(cacheNames = "testCache", sync = true)
+	public Object throwCheckedSync(Object arg1) throws Exception {
+		throw new IOException(arg1.toString());
+	}
+
+	@Override
+	@Cacheable(cacheNames = "testCache", sync = true)
+	public Object throwUncheckedSync(Object arg1) {
+		throw new UnsupportedOperationException(arg1.toString());
+	}
+
 	// multi annotations
 
 	@Override

spring-context/src/test/java/org/springframework/cache/config/CacheableService.java

@@ -29,6 +29,10 @@ public interface CacheableService<T> {
 
 	T cacheNull(Object arg1);
 
+	T cacheSync(Object arg1);
+
+	T cacheSyncNull(Object arg1);
+
 	void invalidate(Object arg1);
 
 	void evictEarly(Object arg1);
@@ -43,6 +47,8 @@ public interface CacheableService<T> {
 
 	T conditional(int field);
 
+	T conditionalSync(int field);
+
 	T unless(int arg);
 
 	T key(Object arg1, Object arg2);
@@ -73,6 +79,10 @@ public interface CacheableService<T> {
 
 	T throwUnchecked(Object arg1);
 
+	T throwCheckedSync(Object arg1) throws Exception;
+
+	T throwUncheckedSync(Object arg1);
+
 	// multi annotations
 	T multiCache(Object arg1);
 

spring-context/src/test/java/org/springframework/cache/config/DefaultCacheableService.java

@@ -48,6 +48,18 @@ public class DefaultCacheableService implements CacheableService<Long> {
 		return null;
 	}
 
+	@Override
+	@Cacheable(cacheNames = "testCache", sync = true)
+	public Long cacheSync(Object arg1) {
+		return counter.getAndIncrement();
+	}
+
+	@Override
+	@Cacheable(cacheNames = "testCache", sync = true)
+	public Long cacheSyncNull(Object arg1) {
+		return null;
+	}
+
 	@Override
 	@CacheEvict("testCache")
 	public void invalidate(Object arg1) {
@@ -82,11 +94,17 @@ public class DefaultCacheableService implements CacheableService<Long> {
 	}
 
 	@Override
-	@Cacheable(cacheNames = "testCache", condition = "#classField == 3")
+	@Cacheable(cacheNames = "testCache", condition = "#p0 == 3")
 	public Long conditional(int classField) {
 		return counter.getAndIncrement();
 	}
 
+	@Override
+	@Cacheable(cacheNames = "testCache", sync = true, condition = "#p0 == 3")
+	public Long conditionalSync(int classField) {
+		return counter.getAndIncrement();
+	}
+
 	@Override
 	@Cacheable(cacheNames = "testCache", unless = "#result > 10")
 	public Long unless(int arg) {
@@ -177,6 +195,18 @@ public class DefaultCacheableService implements CacheableService<Long> {
 		throw new UnsupportedOperationException(arg1.toString());
 	}
 
+	@Override
+	@Cacheable(cacheNames = "testCache", sync = true)
+	public Long throwCheckedSync(Object arg1) throws Exception {
+		throw new IOException(arg1.toString());
+	}
+
+	@Override
+	@Cacheable(cacheNames = "testCache", sync = true)
+	public Long throwUncheckedSync(Object arg1) {
+		throw new UnsupportedOperationException(arg1.toString());
+	}
+
 	// multi annotations
 
 	@Override

spring-context/src/test/java/org/springframework/cache/interceptor/CacheSyncFailureTests.java

@@ -0,0 +1,158 @@
+/*
+ * 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cache.interceptor;
+
+import java.util.concurrent.atomic.AtomicLong;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+
+import org.springframework.cache.CacheManager;
+import org.springframework.cache.CacheTestUtils;
+import org.springframework.cache.annotation.CacheEvict;
+import org.springframework.cache.annotation.Cacheable;
+import org.springframework.cache.annotation.Caching;
+import org.springframework.cache.annotation.CachingConfigurerSupport;
+import org.springframework.cache.annotation.EnableCaching;
+import org.springframework.context.ConfigurableApplicationContext;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+/**
+ * Provides various failure scenario linked to the use of {@link Cacheable#sync()}.
+ *
+ * @author Stephane Nicoll
+ * @since 4.3
+ */
+public class CacheSyncFailureTests {
+
+	@Rule
+	public final ExpectedException thrown = ExpectedException.none();
+
+	private ConfigurableApplicationContext context;
+
+	private SimpleService simpleService;
+
+	@Before
+	public void setUp() {
+		this.context = new AnnotationConfigApplicationContext(Config.class);
+		this.simpleService = context.getBean(SimpleService.class);
+	}
+
+	@After
+	public void closeContext() {
+		if (this.context != null) {
+			this.context.close();
+		}
+	}
+
+	@Test
+	public void unlessSync() {
+		thrown.expect(IllegalStateException.class);
+		thrown.expectMessage("@Cacheable(sync = true) does not support unless attribute");
+		this.simpleService.unlessSync("key");
+	}
+
+	@Test
+	public void severalCachesSync() {
+		thrown.expect(IllegalStateException.class);
+		thrown.expectMessage("@Cacheable(sync = true) only allows a single cache");
+		this.simpleService.severalCachesSync("key");
+	}
+
+	@Test
+	public void severalCachesWithResolvedSync() {
+		thrown.expect(IllegalStateException.class);
+		thrown.expectMessage("@Cacheable(sync = true) only allows a single cache");
+		this.simpleService.severalCachesWithResolvedSync("key");
+	}
+
+	@Test
+	public void syncWithAnotherOperation() {
+		thrown.expect(IllegalStateException.class);
+		thrown.expectMessage("@Cacheable(sync = true) cannot be combined with other cache operations");
+		this.simpleService.syncWithAnotherOperation("key");
+	}
+
+	@Test
+	public void syncWithTwoGetOperations() {
+		thrown.expect(IllegalStateException.class);
+		thrown.expectMessage("Only one @Cacheable(sync = true) entry is allowed");
+		this.simpleService.syncWithTwoGetOperations("key");
+	}
+
+
+	static class SimpleService {
+
+		private final AtomicLong counter = new AtomicLong();
+
+		@Cacheable(cacheNames = "testCache", sync = true, unless = "#result > 10")
+		public Object unlessSync(Object arg1) {
+			return this.counter.getAndIncrement();
+		}
+
+		@Cacheable(cacheNames = {"testCache", "anotherTestCache"}, sync = true)
+		public Object severalCachesSync(Object arg1) {
+			return this.counter.getAndIncrement();
+		}
+
+		@Cacheable(cacheResolver = "testCacheResolver", sync = true)
+		public Object severalCachesWithResolvedSync(Object arg1) {
+			return this.counter.getAndIncrement();
+		}
+
+		@Cacheable(cacheNames = "testCache", sync = true)
+		@CacheEvict(cacheNames = "anotherTestCache", key = "#arg1")
+		public Object syncWithAnotherOperation(Object arg1) {
+			return this.counter.getAndIncrement();
+		}
+
+		@Caching(cacheable = {
+				@Cacheable(cacheNames = "testCache", sync = true),
+				@Cacheable(cacheNames = "anotherTestCache", sync = true)
+		})
+		public Object syncWithTwoGetOperations(Object arg1) {
+			return this.counter.getAndIncrement();
+		}
+	}
+
+	@Configuration
+	@EnableCaching
+	static class Config extends CachingConfigurerSupport {
+
+		@Override
+		@Bean
+		public CacheManager cacheManager() {
+			return CacheTestUtils.createSimpleCacheManager("testCache", "anotherTestCache");
+		}
+
+		@Bean
+		public CacheResolver testCacheResolver() {
+			return new NamedCacheResolver(cacheManager(), "testCache", "anotherTestCache");
+		}
+
+		@Bean
+		public SimpleService simpleService() {
+			return new SimpleService();
+		}
+	}
+
+}

spring-context/src/test/resources/org/springframework/cache/config/cache-advice.xml

@@ -11,7 +11,10 @@
 		<cache:caching cache="testCache">
 			<cache:cacheable method="cache"/>
 			<cache:cacheable method="cacheNull"/>
+			<cache:cacheable method="cacheSync" sync="true"/>
+			<cache:cacheable method="cacheSyncNull" sync="true"/>
 			<cache:cacheable method="conditional" condition="#classField == 3"/>
+			<cache:cacheable method="conditionalSync" sync="true" condition="#classField == 3"/>
 			<cache:cacheable method="unless" unless="#result > 10"/>
 			<cache:cacheable method="key" key="#p0"/>
 			<cache:cacheable method="varArgsKey"/>