Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You 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.apache.commons.pool2; import java.util.NoSuchElementException; /** * A "keyed" pooling interface. * <p> * A keyed pool maintains a pool of instances for each key value. * <p> * Example of use: * <pre style="border:solid thin; padding: 1ex;" * > Object obj = <code style="color:#00C">null</code>; * Object key = <code style="color:#C00">"Key"</code>; * * <code style="color:#00C">try</code> { * obj = pool.borrowObject(key); * <code style="color:#0C0">//...use the object...</code> * } <code style="color:#00C">catch</code>(Exception e) { * <code style="color:#0C0">// invalidate the object</code> * pool.invalidateObject(key, obj); * <code style="color:#0C0">// do not return the object to the pool twice</code> * obj = <code style="color:#00C">null</code>; * } <code style="color:#00C">finally</code> { * <code style="color:#0C0">// make sure the object is returned to the pool</code> * <code style="color:#00C">if</code>(<code style="color:#00C">null</code> != obj) { * pool.returnObject(key, obj); * } * }</pre> * <p> * {@link KeyedObjectPool} implementations <i>may</i> choose to store at most * one instance per key value, or may choose to maintain a pool of instances * for each key (essentially creating a {@link java.util.Map Map} of * {@link ObjectPool pools}). * <p> * See {@link org.apache.commons.pool2.impl.GenericKeyedObjectPool * GenericKeyedObjectPool} for an implementation. * * @param <K> The type of keys maintained by this pool. * @param <V> Type of element pooled in this pool. * * @see KeyedPooledObjectFactory * @see ObjectPool * @see org.apache.commons.pool2.impl.GenericKeyedObjectPool GenericKeyedObjectPool * * @version $Revision: 1566605 $ * * @since 2.0 */ public interface KeyedObjectPool<K, V> { /** * Obtains an instance from this pool for the specified <code>key</code>. * <p> * Instances returned from this method will have been either newly created * with {@link KeyedPooledObjectFactory#makeObject makeObject} or will be * a previously idle object and have been activated with * {@link KeyedPooledObjectFactory#activateObject activateObject} and then * (optionally) validated with * {@link KeyedPooledObjectFactory#validateObject validateObject}. * <p> * By contract, clients <strong>must</strong> return the borrowed object * using {@link #returnObject returnObject}, * {@link #invalidateObject invalidateObject}, or a related method as * defined in an implementation or sub-interface, using a <code>key</code> * that is {@link Object#equals equivalent} to the one used to borrow the * instance in the first place. * <p> * The behaviour of this method when the pool has been exhausted is not * strictly specified (although it may be specified by implementations). * * @param key the key used to obtain the object * * @return an instance from this pool. * * @throws IllegalStateException * after {@link #close close} has been called on this pool * @throws Exception * when {@link KeyedPooledObjectFactory#makeObject * makeObject} throws an exception * @throws NoSuchElementException * when the pool is exhausted and cannot or will not return * another instance */ V borrowObject(K key) throws Exception, NoSuchElementException, IllegalStateException; /** * Return an instance to the pool. By contract, <code>obj</code> * <strong>must</strong> have been obtained using * {@link #borrowObject borrowObject} or a related method as defined in an * implementation or sub-interface using a <code>key</code> that is * equivalent to the one used to borrow the instance in the first place. * * @param key the key used to obtain the object * @param obj a {@link #borrowObject borrowed} instance to be returned. * * @throws IllegalStateException * if an attempt is made to return an object to the pool that * is in any state other than allocated (i.e. borrowed). * Attempting to return an object more than once or attempting * to return an object that was never borrowed from the pool * will trigger this exception. * * @throws Exception if an instance cannot be returned to the pool */ void returnObject(K key, V obj) throws Exception; /** * Invalidates an object from the pool. * <p> * By contract, <code>obj</code> <strong>must</strong> have been obtained * using {@link #borrowObject borrowObject} or a related method as defined * in an implementation or sub-interface using a <code>key</code> that is * equivalent to the one used to borrow the <code>Object</code> in the first * place. * <p> * This method should be used when an object that has been borrowed is * determined (due to an exception or other problem) to be invalid. * * @param key the key used to obtain the object * @param obj a {@link #borrowObject borrowed} instance to be returned. * * @throws Exception if the instance cannot be invalidated */ void invalidateObject(K key, V obj) throws Exception; /** * Create an object using the {@link KeyedPooledObjectFactory factory} or * other implementation dependent mechanism, passivate it, and then place it * in the idle object pool. <code>addObject</code> is useful for * "pre-loading" a pool with idle objects (Optional operation). * * @param key the key a new instance should be added to * * @throws Exception * when {@link KeyedPooledObjectFactory#makeObject} fails. * @throws IllegalStateException * after {@link #close} has been called on this pool. * @throws UnsupportedOperationException * when this pool cannot add new idle objects. */ void addObject(K key) throws Exception, IllegalStateException, UnsupportedOperationException; /** * Returns the number of instances corresponding to the given * <code>key</code> currently idle in this pool. Returns a negative value if * this information is not available. * * @param key the key to query * @return the number of instances corresponding to the given * <code>key</code> currently idle in this pool. */ int getNumIdle(K key); /** * Returns the number of instances currently borrowed from but not yet * returned to the pool corresponding to the given <code>key</code>. * Returns a negative value if this information is not available. * * @param key the key to query * @return the number of instances currently borrowed from but not yet * returned to the pool corresponding to the given <code>key</code>. = */ int getNumActive(K key); /** * Returns the total number of instances currently idle in this pool. * Returns a negative value if this information is not available. * @return the total number of instances currently idle in this pool. = */ int getNumIdle(); /** * Returns the total number of instances current borrowed from this pool but * not yet returned. Returns a negative value if this information is not * available. * @return the total number of instances current borrowed from this pool but * not yet returned. */ int getNumActive(); /** * Clears the pool, removing all pooled instances (optional operation). * * @throws UnsupportedOperationException when this implementation doesn't * support the operation * * @throws Exception if the pool cannot be cleared */ void clear() throws Exception, UnsupportedOperationException; /** * Clears the specified pool, removing all pooled instances corresponding to * the given <code>key</code> (optional operation). * * @param key the key to clear * * @throws UnsupportedOperationException when this implementation doesn't * support the operation * * @throws Exception if the key cannot be cleared */ void clear(K key) throws Exception, UnsupportedOperationException; /** * Close this pool, and free any resources associated with it. * <p> * Calling {@link #addObject addObject} or * {@link #borrowObject borrowObject} after invoking this method on a pool * will cause them to throw an {@link IllegalStateException}. * <p> * Implementations should silently fail if not all resources can be freed. */ void close(); }