Add putIfAbsent on Cache abstraction

This commit adds a putIfAbsent method to the Cache interface. This
method offers an atomic put if the key is not already associated in
the cache.

Issue: SPR-11400

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

@@ -29,6 +29,7 @@ import org.springframework.util.Assert;
  *
  * @author Costin Leau
  * @author Juergen Hoeller
+ * @author Stephane Nicoll
  * @since 3.1
  */
 public class EhCacheCache implements Cache {
@@ -62,7 +63,7 @@ public class EhCacheCache implements Cache {
 	@Override
 	public ValueWrapper get(Object key) {
 		Element element = this.cache.get(key);
-		return (element != null ? new SimpleValueWrapper(element.getObjectValue()) : null);
+		return toWrapper(element);
 	}
 
 	@Override
@@ -81,6 +82,12 @@ public class EhCacheCache implements Cache {
 		this.cache.put(new Element(key, value));
 	}
 
+	@Override
+	public ValueWrapper putIfAbsent(Object key, Object value) {
+		Element existingElement = this.cache.putIfAbsent(new Element(key, value));
+		return toWrapper(existingElement);
+	}
+
 	@Override
 	public void evict(Object key) {
 		this.cache.remove(key);
@@ -91,4 +98,8 @@ public class EhCacheCache implements Cache {
 		this.cache.removeAll();
 	}
 
+	private ValueWrapper toWrapper(Element element) {
+		return (element != null ? new SimpleValueWrapper(element.getObjectValue()) : null);
+	}
+
 }

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

@@ -17,6 +17,8 @@
 package org.springframework.cache.guava;
 
 import java.io.Serializable;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutionException;
 
 import org.springframework.cache.Cache;
 import org.springframework.cache.support.SimpleValueWrapper;
@@ -29,6 +31,7 @@ import org.springframework.util.Assert;
  * <p>Requires Google Guava 12.0 or higher.
  *
  * @author Juergen Hoeller
+ * @author Stephane Nicoll
  * @since 4.0
  */
 public class GuavaCache implements Cache {
@@ -83,7 +86,7 @@ public class GuavaCache implements Cache {
 	@Override
 	public ValueWrapper get(Object key) {
 		Object value = this.cache.getIfPresent(key);
-		return (value != null ? new SimpleValueWrapper(fromStoreValue(value)) : null);
+		return toWrapper(value);
 	}
 
 	@Override
@@ -101,6 +104,17 @@ public class GuavaCache implements Cache {
 		this.cache.put(key, toStoreValue(value));
 	}
 
+	@Override
+	public ValueWrapper putIfAbsent(Object key, final Object value) {
+		try {
+			PutIfAbsentCallable callable = new PutIfAbsentCallable(value);
+			Object result = this.cache.get(key, callable);
+			return (callable.called ? null : toWrapper(result));
+		} catch (ExecutionException e) {
+			throw new IllegalArgumentException(e);
+		}
+	}
+
 	@Override
 	public void evict(Object key) {
 		this.cache.invalidate(key);
@@ -138,9 +152,29 @@ public class GuavaCache implements Cache {
 		return userValue;
 	}
 
+	private ValueWrapper toWrapper(Object value) {
+		return (value != null ? new SimpleValueWrapper(fromStoreValue(value)) : null);
+	}
+
 
 	@SuppressWarnings("serial")
 	private static class NullHolder implements Serializable {
 	}
 
+	private class PutIfAbsentCallable implements Callable<Object> {
+		private boolean called;
+
+		private final Object value;
+
+		private PutIfAbsentCallable(Object value) {
+			this.value = value;
+		}
+
+		@Override
+		public Object call() throws Exception {
+			called = true;
+			return toStoreValue(value);
+		}
+	}
+
 }

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

@@ -29,6 +29,7 @@ import org.springframework.util.Assert;
  * <p>Note: This class has been updated for JCache 1.0, as of Spring 4.0.
  *
  * @author Juergen Hoeller
+ * @author Stephane Nicoll
  * @since 3.2
  */
 public class JCacheCache implements Cache {
@@ -95,6 +96,12 @@ public class JCacheCache implements Cache {
 		this.cache.put(key, toStoreValue(value));
 	}
 
+	@Override
+	public ValueWrapper putIfAbsent(Object key, Object value) {
+		boolean set = this.cache.putIfAbsent(key, toStoreValue(value));
+		return (set ? null : get(key));
+	}
+
 	@Override
 	public void evict(Object key) {
 		this.cache.remove(key);

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2013 the original author or authors.
+ * 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.
@@ -28,7 +28,11 @@ import org.springframework.util.Assert;
  * successful transaction. If no transaction is active, {@link #put} and {@link #evict}
  * operations will be performed immediately, as usual.
  *
+ * <p>Use of more aggressive operations such as {@link #putIfAbsent} cannot be deferred
+ * to the after-commit phase of a running transaction. Use these with care.
+ *
  * @author Juergen Hoeller
+ * @author Stephane Nicoll
  * @since 3.2
  * @see TransactionAwareCacheManagerProxy
  */
@@ -82,6 +86,11 @@ public class TransactionAwareCacheDecorator implements Cache {
 		}
 	}
 
+	@Override
+	public ValueWrapper putIfAbsent(final Object key, final Object value) {
+		return this.targetCache.putIfAbsent(key, value);
+	}
+
 	@Override
 	public void evict(final Object key) {
 		if (TransactionSynchronizationManager.isSynchronizationActive()) {