* 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.wamblee.cache;
import java.io.Serializable;
/**
- * The <code>Cache</code> interface represents... a cache. In some circumstances
- * it is more optimal to implement caching directly in the code instead of
- * relying on Hibernate caching methods. This interface abstracts from the used
- * cache implementation. Cache implementations must be thread-safe.
+ * The <code>Cache</code> interface represents a cache intended for
+ * application-level caching. In some circumstances it is more optimal to
+ * implement caching directly in the code instead of relying on Hibernate
+ * caching methods. This interface abstracts from the used cache implementation.
+ * Cache implementations must be thread-safe.
*/
public interface Cache<KeyType extends Serializable, ValueType extends Serializable> {
/**
* @param aKey
* Key to retrieve.
*
- * @return Key.
+ * @return Value or null if expired..
*/
ValueType get(KeyType aKey);
* 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.wamblee.cache;
-import org.apache.log4j.Logger;
-
import java.io.Serializable;
+import java.util.logging.Level;
+import java.util.logging.Logger;
/**
- * Represents a cached object. The object is either retrieved from the cache if
- * the cache has it, or a call back is invoked to get the object (and put it in
- * the cache).
+ * Represents a cached object identified by the key it has in a certain
+ * {@link Cache}. The object is either retrieved from the cache if the cache has
+ * it, or a call back is invoked to get the object (and put it in the cache).
*
* @author Erik Brakkee
*
*/
public class CachedObject<KeyType extends Serializable, ValueType extends Serializable> {
- private static final Logger LOGGER = Logger.getLogger(CachedObject.class);
+ private static final Logger LOGGER = Logger.getLogger(CachedObject.class
+ .getName());
/**
* Cache to use.
*/
private KeyType objectKey;
+ /**
+ * Last known value.
+ */
+ private ValueType value;
+
+ /**
+ * Are we now computing the value or not?
+ */
+ private boolean computing;
+
/**
* Computation used to obtain the object if it is not found in the cache.
*/
* Gets the object. Since the object is cached, different calls to this
* method may return different objects.
*
+ * If the object is expired from the cache it is recomputed using the
+ * callback. In case the callback throws an exception the
+ * last known value is used. In case an exception is thrown, the problem is
+ * also logged. In case a recomputation is already being done by another
+ * thread, the last known value is immediately returned.
+ *
* @return Object.
*/
public ValueType get() {
- ValueType object = (ValueType) cache.get(objectKey); // the used
- // cache is
- // thread safe.
-
- if (object == null) {
- // synchronize the computation to make sure that the object is only
- // computed
- // once when multiple concurrent threads detect that the entry must
- // be
- // recomputed.
+ synchronized (this) {
+ if (computing) {
+ // always return old value while computing.
+ return value;
+ }
+
+ ValueType cachedValue = cache.get(objectKey);
+ if (cachedValue == null) {
+ // expired
+ computing = true;
+ } else {
+ // no change.
+ return value;
+ }
+ }
+ try {
+
+ // we only get here if we are computing
+ // do the computation without holding the lock.
+ LOGGER.fine("Refreshing cache for '" + objectKey + "'");
+ ValueType object = computation.getObject(objectKey);
+ cache.put(objectKey, object);
+
+ synchronized (this) {
+ value = object;
+ }
+ } catch (Exception e) {
+ LOGGER.log(Level.INFO,
+ "Recomputation of cached item failed for key '" + objectKey +
+ "'", e);
+ } finally {
synchronized (this) {
- object = (ValueType) cache.get(objectKey);
-
- if (object == null) {
- // No other thread did a recomputation so we must do this
- // now.
- LOGGER.debug("Refreshing cache for '" + objectKey + "'");
- object = computation.getObject(objectKey);
- cache.put(objectKey, object);
- }
+ computing = false;
}
}
- return object;
+ return value;
}
/**
public static interface Computation<Key extends Serializable, Value extends Serializable> {
/**
* Gets the object. Called when the object is not in the cache.
+ * In case computation fails, an exception should be thrown to ensure that the last
+ * known value will be used.
*
* @param aObjectKey
* Id of the object in the cache.
*
* @return Object, must be non-null.
*/
- Value getObject(Key aObjectKey);
+ Value getObject(Key aObjectKey) throws Exception;
}
}
import net.sf.ehcache.CacheManager;
import net.sf.ehcache.Element;
-import org.apache.log4j.Logger;
import org.wamblee.io.InputResource;
import java.io.IOException;
import java.io.InputStream;
import java.io.Serializable;
+import java.util.logging.Logger;
/**
* Cache implemented on top of EhCache.
*/
public class EhCache<KeyType extends Serializable, ValueType extends Serializable>
implements org.wamblee.cache.Cache<KeyType, ValueType> {
- private static final Logger LOGGER = Logger.getLogger(EhCache.class);
+ private static final Logger LOGGER = Logger.getLogger(EhCache.class.getName());
/**
* EH Cache manager.
cache = manager.getCache(aCacheName);
if (cache == null) {
- LOGGER.warn("Creating cache '" + aCacheName +
+ LOGGER.warning("Creating cache '" + aCacheName +
"' because it is not configured");
manager.addCache(aCacheName);
cache = manager.getCache(aCacheName);
--- /dev/null
+/*
+ * Copyright 2005-2010 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.
+ */
+/**
+ * This package provides an interface for a cache together with several implementations.
+ * The main interfaces and classes are:
+ * <ul>
+ * <li> {@link Cache}: An interface representing an application-level cache with objects in the
+ * cache identified by keys.
+ * </li>
+ * <li> {@link CachedObject}: An object representing an object in a cache identified through a
+ * key. Upon expiry the cached object invokes a callback to recompute (and cache) the object
+ * again.
+ * </li>
+ * <li> {@link ComputedValue}: An object caching a computed value with a computation interface
+ * determining whether the object is out of date and allowing recomputation of the value.
+ * </li>
+ * </ul>
+ */
+package org.wamblee.cache;
\ No newline at end of file
+++ /dev/null
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
-<html>
-<head>
- wamblee.org
-</head>
-<body bgcolor="white">
-
-This package provides an interface for a cache together with several
-implementations.
-
-<!-- Put @see and @since tags down here. -->
-
-@since -
-
-</body>
-</html>
git://wamblee.org / utils / commitdiff