Restore proper use of CacheLoader

Since Guava 11, CacheLoader is only invoked with a LoadingCache but the
GuavaCache wrapper is always invoking getIfPresent(), available on the
main Guava Cache interface.

Update GuavaCache#get to check for the presence of a LoadingCache and
call the appropriate method.

Issue: SPR-12842

Author: snicoll

spring-context-support/src/main/java/org/springframework/cache/guava/GuavaCache.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 +20,9 @@
 import java.util.concurrent.Callable;
 import java.util.concurrent.ExecutionException;
 
+import com.google.common.cache.LoadingCache;
+import com.google.common.util.concurrent.UncheckedExecutionException;
+
 import org.springframework.cache.Cache;
 import org.springframework.cache.support.SimpleValueWrapper;
 import org.springframework.util.Assert;
@@ -88,8 +91,16 @@ public final boolean isAllowNullValues() {
 
 	@Override
 	public ValueWrapper get(Object key) {
-		Object value = this.cache.getIfPresent(key);
-		return toWrapper(value);
+		if (this.cache instanceof LoadingCache) {
+			try {
+				Object value = ((LoadingCache<Object, Object>) this.cache).get(key);
+				return toWrapper(value);
+			}
+			catch (ExecutionException ex) {
+				throw new UncheckedExecutionException(ex.getMessage(), ex);
+			}
+		}
+		return toWrapper(this.cache.getIfPresent(key));
 	}
 
 	@Override

spring-context-support/src/test/java/org/springframework/cache/guava/GuavaCacheManagerTests.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.
@@ -18,7 +18,10 @@
 
 import com.google.common.cache.CacheBuilder;
 import com.google.common.cache.CacheLoader;
+import com.google.common.util.concurrent.UncheckedExecutionException;
+import org.junit.Rule;
 import org.junit.Test;
+import org.junit.rules.ExpectedException;
 
 import org.springframework.cache.Cache;
 import org.springframework.cache.CacheManager;
@@ -32,6 +35,9 @@
  */
 public class GuavaCacheManagerTests {
 
+	@Rule
+	public final ExpectedException thrown = ExpectedException.none();
+
 	@Test
 	public void testDynamicMode() {
 		CacheManager cm = new GuavaCacheManager();
@@ -150,6 +156,28 @@ public void setCacheNameNullRestoreDynamicMode() {
 		assertNotNull(cm.getCache("someCache"));
 	}
 
+	@Test
+	public void cacheLoaderUseLoadingCache() {
+		GuavaCacheManager cm = new GuavaCacheManager("c1");
+		cm.setCacheLoader(new CacheLoader<Object, Object>() {
+			@Override
+			public Object load(Object key) throws Exception {
+				if ("ping".equals(key)) {
+					return "pong";
+				}
+				throw new IllegalArgumentException("I only know ping");
+			}
+		});
+		Cache cache1 = cm.getCache("c1");
+		Cache.ValueWrapper value = cache1.get("ping");
+		assertNotNull(value);
+		assertEquals("pong", value.get());
+
+		thrown.expect(UncheckedExecutionException.class);
+		thrown.expectMessage("I only know ping");
+		assertNull(cache1.get("foo"));
+	}
+
 	@SuppressWarnings("unchecked")
 	private CacheLoader<Object, Object> mockCacheLoader() {
 		return mock(CacheLoader.class);