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.pool; import java.util.NoSuchElementException; /** * A "keyed" pooling interface. * <p> * A keyed pool pools instances of multiple types. Each * type may be accessed using an arbitrary key. * </p> * <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> * <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> * * <p>See {@link BaseKeyedObjectPool} for a simple base implementation.</p> * * @author Rodney Waldhoff * @author Sandy McArthur * @version $Revision: 778480 $ $Date: 2009-05-25 15:34:55 -0400 (Mon, 25 May 2009) $ * @see KeyedPoolableObjectFactory * @see KeyedObjectPoolFactory * @see ObjectPool * @see BaseKeyedObjectPool * @since Pool 1.0 */ public interface KeyedObjectPool { /** * 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 KeyedPoolableObjectFactory#makeObject makeObject} or will be a previously idle object and * have been activated with {@link KeyedPoolableObjectFactory#activateObject activateObject} and * then validated with {@link KeyedPoolableObjectFactory#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). * Older versions of this method would return <code>null</code> to indicate exhaustion, * newer versions are encouraged to throw a {@link NoSuchElementException}. * * @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 KeyedPoolableObjectFactory#makeObject makeObject} throws an exception * @throws NoSuchElementException when the pool is exhausted and cannot or will not return another instance */ Object borrowObject(Object 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 Exception */ void returnObject(Object key, Object obj) throws Exception; /** * Invalidates an object from 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 <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. * </p> * * @param key the key used to obtain the object * @param obj a {@link #borrowObject borrowed} instance to be returned. * @throws Exception */ void invalidateObject(Object key, Object obj) throws Exception; /** * Create an object using the {@link KeyedPoolableObjectFactory 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 KeyedPoolableObjectFactory#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(Object key) throws Exception, IllegalStateException, UnsupportedOperationException; /** * Returns the number of instances * corresponding to the given <code>key</code> * currently idle in this pool (optional operation). * 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 or a negative value if unsupported * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation */ int getNumIdle(Object key) throws UnsupportedOperationException; /** * Returns the number of instances * currently borrowed from but not yet returned * to the pool corresponding to the * given <code>key</code> (optional operation). * 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 borrowed in this pool or a negative value if unsupported * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation */ int getNumActive(Object key) throws UnsupportedOperationException; /** * Returns the total number of instances * currently idle in this pool (optional operation). * Returns a negative value if this information is not available. * * @return the total number of instances currently idle in this pool or a negative value if unsupported * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation */ int getNumIdle() throws UnsupportedOperationException; /** * Returns the total number of instances * current borrowed from this pool but not * yet returned (optional operation). * Returns a negative value if this information is not available. * * @return the total number of instances currently borrowed from this pool or a negative value if unsupported * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation */ int getNumActive() throws UnsupportedOperationException; /** * Clears the pool, removing all pooled instances (optional operation). * Throws {@link UnsupportedOperationException} if the pool cannot be cleared. * * @throws UnsupportedOperationException when this implementation doesn't support the operation */ void clear() throws Exception, UnsupportedOperationException; /** * Clears the specified pool, removing all * pooled instances corresponding to * the given <code>key</code> (optional operation). * Throws {@link UnsupportedOperationException} if the pool cannot be cleared. * * @param key the key to clear * @throws UnsupportedOperationException when this implementation doesn't support the operation */ void clear(Object 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> * * @throws Exception */ void close() throws Exception; /** * Sets the {@link KeyedPoolableObjectFactory factory} the pool uses * to create new instances (optional operation). * Trying to change the <code>factory</code> after a pool has been used will frequently * throw an {@link UnsupportedOperationException}. It is up to the pool * implementation to determine when it is acceptable to call this method. * * @param factory the {@link KeyedPoolableObjectFactory} used to create new instances. * @throws IllegalStateException when the factory cannot be set at this time * @throws UnsupportedOperationException when this implementation doesn't support the operation */ void setFactory(KeyedPoolableObjectFactory factory) throws IllegalStateException, UnsupportedOperationException; }