    001    /*
    002     * Licensed to the Apache Software Foundation (ASF) under one or more
    003     * contributor license agreements.  See the NOTICE file distributed with
    004     * this work for additional information regarding copyright ownership.
    005     * The ASF licenses this file to You under the Apache License, Version 2.0
    006     * (the "License"); you may not use this file except in compliance with
    007     * the License.  You may obtain a copy of the License at
    008     *
    009     *      http://www.apache.org/licenses/LICENSE-2.0
    010     *
    011     * Unless required by applicable law or agreed to in writing, software
    012     * distributed under the License is distributed on an "AS IS" BASIS,
    013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014     * See the License for the specific language governing permissions and
    015     * limitations under the License.
    016     */
    017
    018    package org.apache.commons.pool;
    019
    020    import java.util.NoSuchElementException;
    021
    022    /**
    023     * A "keyed" pooling interface.
    024     * <p>
    025     * A keyed pool pools instances of multiple types. Each
    026     * type may be accessed using an arbitrary key.
    027     * </p>
    028     * <p>
    029     * Example of use:
    030     * <pre style="border:solid thin; padding: 1ex;"
    031     * > Object obj = <code style="color:#00C">null</code>;
    032     * Object key = <code style="color:#C00">"Key"</code>;
    033     *
    034     * <code style="color:#00C">try</code> {
    035     *     obj = pool.borrowObject(key);
    036     *     <code style="color:#0C0">//...use the object...</code>
    037     * } <code style="color:#00C">catch</code>(Exception e) {
    038     *     <code style="color:#0C0">// invalidate the object</code>
    039     *     pool.invalidateObject(key, obj);
    040     *     <code style="color:#0C0">// do not return the object to the pool twice</code>
    041     *     obj = <code style="color:#00C">null</code>;
    042     * } <code style="color:#00C">finally</code> {
    043     *     <code style="color:#0C0">// make sure the object is returned to the pool</code>
    044     *     <code style="color:#00C">if</code>(<code style="color:#00C">null</code> != obj) {
    045     *         pool.returnObject(key, obj);
    046     *     }
    047     * }</pre>
    048     * </p>
    049     * <p>
    050     * {@link KeyedObjectPool} implementations <i>may</i> choose to store at most
    051     * one instance per key value, or may choose to maintain a pool of instances
    052     * for each key (essentially creating a {@link java.util.Map Map} of
    053     * {@link ObjectPool pools}).
    054     * </p>
    055     *
    056     * <p>See {@link BaseKeyedObjectPool} for a simple base implementation.</p>
    057     *
    058     * @author Rodney Waldhoff
    059     * @author Sandy McArthur
    060     * @version $Revision: 962893 $ $Date: 2010-07-10 10:37:27 -0700 (Sat, 10 Jul 2010) $
    061     * @see KeyedPoolableObjectFactory
    062     * @see KeyedObjectPoolFactory
    063     * @see ObjectPool
    064     * @see BaseKeyedObjectPool
    065     * @since Pool 1.0
    066     */
    067    public interface KeyedObjectPool {
    068        /**
    069         * Obtains an instance from this pool for the specified <code>key</code>.
    070         * <p>
    071         * Instances returned from this method will have been either newly created with
    072         * {@link KeyedPoolableObjectFactory#makeObject makeObject} or will be a previously idle object and
    073         * have been activated with {@link KeyedPoolableObjectFactory#activateObject activateObject} and
    074         * then validated with {@link KeyedPoolableObjectFactory#validateObject validateObject}.
    075         * <p>
    076         * By contract, clients <strong>must</strong> return the borrowed object using
    077         * {@link #returnObject returnObject}, {@link #invalidateObject invalidateObject}, or a related method
    078         * as defined in an implementation or sub-interface,
    079         * using a <code>key</code> that is {@link Object#equals equivalent} to the one used to
    080         * borrow the instance in the first place.
    081         * <p>
    082         * The behaviour of this method when the pool has been exhausted
    083         * is not strictly specified (although it may be specified by implementations).
    084         * Older versions of this method would return <code>null</code> to indicate exhaustion,
    085         * newer versions are encouraged to throw a {@link NoSuchElementException}.
    086         *
    087         * @param key the key used to obtain the object
    088         * @return an instance from this pool.
    089         * @throws IllegalStateException after {@link #close close} has been called on this pool
    090         * @throws Exception when {@link KeyedPoolableObjectFactory#makeObject makeObject} throws an exception
    091         * @throws NoSuchElementException when the pool is exhausted and cannot or will not return another instance
    092         */
    093        Object borrowObject(Object key) throws Exception, NoSuchElementException, IllegalStateException;
    094
    095        /**
    096         * Return an instance to the pool.
    097         * By contract, <code>obj</code> <strong>must</strong> have been obtained
    098         * using {@link #borrowObject borrowObject}
    099         * or a related method as defined in an implementation
    100         * or sub-interface
    101         * using a <code>key</code> that is equivalent to the one used to
    102         * borrow the instance in the first place.
    103         *
    104         * @param key the key used to obtain the object
    105         * @param obj a {@link #borrowObject borrowed} instance to be returned.
    106         * @throws Exception
    107         */
    108        void returnObject(Object key, Object obj) throws Exception;
    109
    110        /**
    111         * <p>Invalidates an object from the pool.</p>
    112         *
    113         * <p>By contract, <code>obj</code> <strong>must</strong> have been obtained
    114         * using {@link #borrowObject borrowObject} or a related method as defined
    115         * in an implementation or sub-interface using a <code>key</code> that is
    116         * equivalent to the one used to borrow the <code>Object</code> in the first place.</p>
    117         *
    118         * <p>This method should be used when an object that has been borrowed
    119         * is determined (due to an exception or other problem) to be invalid.</p>
    120         *
    121         * @param key the key used to obtain the object
    122         * @param obj a {@link #borrowObject borrowed} instance to be returned.
    123         * @throws Exception
    124         */
    125        void invalidateObject(Object key, Object obj) throws Exception;
    126
    127        /**
    128         * Create an object using the {@link KeyedPoolableObjectFactory factory} or other
    129         * implementation dependent mechanism, passivate it, and then place it in the idle object pool.
    130         * <code>addObject</code> is useful for "pre-loading" a pool with idle objects
    131         * (Optional operation).
    132         *
    133         * @param key the key a new instance should be added to
    134         * @throws Exception when {@link KeyedPoolableObjectFactory#makeObject} fails.
    135         * @throws IllegalStateException after {@link #close} has been called on this pool.
    136         * @throws UnsupportedOperationException when this pool cannot add new idle objects.
    137         */
    138        void addObject(Object key) throws Exception, IllegalStateException, UnsupportedOperationException;
    139
    140        /**
    141         * Returns the number of instances
    142         * corresponding to the given <code>key</code>
    143         * currently idle in this pool (optional operation).
    144         * Returns a negative value if this information is not available.
    145         *
    146         * @param key the key to query
    147         * @return the number of instances corresponding to the given <code>key</code> currently idle in this pool or a negative value if unsupported
    148         * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
    149         */
    150        int getNumIdle(Object key) throws UnsupportedOperationException;
    151
    152        /**
    153         * Returns the number of instances
    154         * currently borrowed from but not yet returned
    155         * to the pool corresponding to the
    156         * given <code>key</code> (optional operation).
    157         * Returns a negative value if this information is not available.
    158         *
    159         * @param key the key to query
    160         * @return the number of instances corresponding to the given <code>key</code> currently borrowed in this pool or a negative value if unsupported
    161         * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
    162         */
    163        int getNumActive(Object key) throws UnsupportedOperationException;
    164
    165        /**
    166         * Returns the total number of instances
    167         * currently idle in this pool (optional operation).
    168         * Returns a negative value if this information is not available.
    169         *
    170         * @return the total number of instances currently idle in this pool or a negative value if unsupported
    171         * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
    172         */
    173        int getNumIdle() throws UnsupportedOperationException;
    174
    175        /**
    176         * Returns the total number of instances
    177         * current borrowed from this pool but not
    178         * yet returned (optional operation).
    179         * Returns a negative value if this information is not available.
    180         *
    181         * @return the total number of instances currently borrowed from this pool or a negative value if unsupported
    182         * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
    183         */
    184        int getNumActive() throws UnsupportedOperationException;
    185
    186        /**
    187         * Clears the pool, removing all pooled instances (optional operation).
    188         * Throws {@link UnsupportedOperationException} if the pool cannot be cleared.
    189         *
    190         * @throws UnsupportedOperationException when this implementation doesn't support the operation
    191         */
    192        void clear() throws Exception, UnsupportedOperationException;
    193
    194        /**
    195         * Clears the specified pool, removing all
    196         * pooled instances corresponding to
    197         * the given <code>key</code> (optional operation).
    198         * Throws {@link UnsupportedOperationException} if the pool cannot be cleared.
    199         *
    200         * @param key the key to clear
    201         * @throws UnsupportedOperationException when this implementation doesn't support the operation
    202         */
    203        void clear(Object key) throws Exception, UnsupportedOperationException;
    204
    205        /**
    206         * Close this pool, and free any resources associated with it.
    207         * <p>
    208         * Calling {@link #addObject addObject} or {@link #borrowObject borrowObject} after invoking
    209         * this method on a pool will cause them to throw an {@link IllegalStateException}.
    210         * </p>
    211         *
    212         * @throws Exception
    213         */
    214        void close() throws Exception;
    215
    216        /**
    217         * Sets the {@link KeyedPoolableObjectFactory factory} the pool uses
    218         * to create new instances (optional operation).
    219         * Trying to change the <code>factory</code> after a pool has been used will frequently
    220         * throw an {@link UnsupportedOperationException}. It is up to the pool
    221         * implementation to determine when it is acceptable to call this method.
    222         *
    223         * @param factory the {@link KeyedPoolableObjectFactory} used to create new instances.
    224         * @throws IllegalStateException when the factory cannot be set at this time
    225         * @throws UnsupportedOperationException when this implementation doesn't support the operation
    226         * @deprecated to be removed in pool 2.0
    227         */
    228        void setFactory(KeyedPoolableObjectFactory factory) throws IllegalStateException, UnsupportedOperationException;
    229    }