/*
* Copyright 2005 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.wamblee.cache;
+import org.apache.log4j.Logger;
+
import java.io.Serializable;
-import org.apache.log4j.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. 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
+ *
+ * @param <KeyType> DOCUMENT ME!
+ * @param <ValueType> DOCUMENT ME!
*/
public class CachedObject<KeyType extends Serializable, ValueType extends Serializable> {
-
- private static final Logger LOGGER = Logger.getLogger(CachedObject.class);
-
/**
- * Callback invoked to compute an object if it was not found in the cache.
- *
- * @param <T>
- * Type of the object
+ * DOCUMENT ME!
*/
- public static interface Computation<Key extends Serializable, Value extends Serializable> {
- /**
- * Gets the object. Called when the object is not in the cache.
- *
- * @param aObjectKey
- * Id of the object in the cache.
- * @return Object, must be non-null.
- */
- Value getObject(Key aObjectKey);
- }
+ private static final Logger LOGGER = Logger.getLogger(CachedObject.class);
/**
* Cache to use.
private KeyType objectKey;
/**
- * Computation used to obtain the object if it is not found in the cache.
+ * Computation used to obtain the object if it is not found in the
+ * cache.
*/
private Computation<KeyType, ValueType> computation;
- /**
+/**
* Constructs the cached object.
- *
+ *
* @param aCache
* Cache to use.
* @param aObjectKey
* cache.
*/
public CachedObject(Cache<KeyType, ValueType> aCache, KeyType aObjectKey,
- Computation<KeyType, ValueType> aComputation) {
- cache = aCache;
- objectKey = aObjectKey;
- computation = aComputation;
+ Computation<KeyType, ValueType> aComputation) {
+ cache = aCache;
+ objectKey = aObjectKey;
+ computation = aComputation;
}
/**
- * Gets the object. Since the object is cached, different calls to this
- * method may return different objects.
- *
+ * Gets the object. Since the object is cached, different calls to
+ * this method may return different objects.
+ *
* @return Object.
*/
public ValueType get() {
ValueType object = (ValueType) cache.get(objectKey); // the used
- // cache is
- // thread safe.
+ // cache is
+ // thread safe.
+
if (object == null) {
// synchronize the computation to make sure that the object is only
// computed
// recomputed.
synchronized (this) {
object = (ValueType) cache.get(objectKey);
+
if (object == null) {
// No other thread did a recomputation so we must do this
// now.
}
}
}
+
return object;
}
/**
- * Invalidates the cache for the object so that it is recomputed the next
- * time it is requested.
- *
+ * Invalidates the cache for the object so that it is recomputed
+ * the next time it is requested.
*/
public void invalidate() {
cache.remove(objectKey);
/**
* Gets the cache.
- *
+ *
* @return Cache.
*/
public Cache getCache() {
return cache;
}
+
+/**
+ * Callback invoked to compute an object if it was not found in the cache.
+ *
+ * @param <T>
+ * Type of the object
+ */
+ public static interface Computation<Key extends Serializable, Value extends Serializable> {
+ /**
+ * Gets the object. Called when the object is not in the
+ * cache.
+ *
+ * @param aObjectKey Id of the object in the cache.
+ *
+ * @return Object, must be non-null.
+ */
+ Value getObject(Key aObjectKey);
+ }
}