    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 pooling interface.
    024     * <p>
    025     * <code>ObjectPool</code> defines a trivially simple pooling interface. The only
    026     * required methods are {@link #borrowObject borrowObject}, {@link #returnObject returnObject}
    027     * and {@link #invalidateObject invalidateObject}.
    028     * </p>
    029     * <p>
    030     * Example of use:
    031     * <pre style="border:solid thin; padding: 1ex;"
    032     * > Object obj = <code style="color:#00C">null</code>;
    033     *
    034     * <code style="color:#00C">try</code> {
    035     *     obj = pool.borrowObject();
    036     *     <code style="color:#00C">try</code> {
    037     *         <code style="color:#0C0">//...use the object...</code>
    038     *     } <code style="color:#00C">catch</code>(Exception e) {
    039     *         <code style="color:#0C0">// invalidate the object</code>
    040     *         pool.invalidateObject(obj);
    041     *         <code style="color:#0C0">// do not return the object to the pool twice</code>
    042     *         obj = <code style="color:#00C">null</code>;
    043     *     } <code style="color:#00C">finally</code> {
    044     *         <code style="color:#0C0">// make sure the object is returned to the pool</code>
    045     *         <code style="color:#00C">if</code>(<code style="color:#00C">null</code> != obj) {
    046     *             pool.returnObject(obj);
    047     *        }
    048     *     }
    049     * } <code style="color:#00C">catch</code>(Exception e) {
    050     *       <code style="color:#0C0">// failed to borrow an object</code>
    051     * }</pre>
    052     * </p>
    053     *
    054     * <p>See {@link BaseObjectPool} for a simple base implementation.</p>
    055     *
    056     * @author Rodney Waldhoff
    057     * @author Sandy McArthur
    058     * @version $Revision: 962893 $ $Date: 2010-07-10 10:37:27 -0700 (Sat, 10 Jul 2010) $
    059     * @see PoolableObjectFactory
    060     * @see ObjectPoolFactory
    061     * @see KeyedObjectPool
    062     * @see BaseObjectPool
    063     * @since Pool 1.0
    064     */
    065    public interface ObjectPool {
    066        /**
    067         * Obtains an instance from this pool.
    068         * <p>
    069         * Instances returned from this method will have been either newly created with
    070         * {@link PoolableObjectFactory#makeObject makeObject} or will be a previously idle object and
    071         * have been activated with {@link PoolableObjectFactory#activateObject activateObject} and
    072         * then validated with {@link PoolableObjectFactory#validateObject validateObject}.
    073         * </p>
    074         * <p>
    075         * By contract, clients <strong>must</strong> return the borrowed instance using
    076         * {@link #returnObject returnObject}, {@link #invalidateObject invalidateObject}, or a related method
    077         * as defined in an implementation or sub-interface.
    078         * </p>
    079         * <p>
    080         * The behaviour of this method when the pool has been exhausted
    081         * is not strictly specified (although it may be specified by implementations).
    082         * Older versions of this method would return <code>null</code> to indicate exhaustion,
    083         * newer versions are encouraged to throw a {@link NoSuchElementException}.
    084         * </p>
    085         *
    086         * @return an instance from this pool.
    087         * @throws IllegalStateException after {@link #close close} has been called on this pool.
    088         * @throws Exception when {@link PoolableObjectFactory#makeObject makeObject} throws an exception.
    089         * @throws NoSuchElementException when the pool is exhausted and cannot or will not return another instance.
    090         */
    091        Object borrowObject() throws Exception, NoSuchElementException, IllegalStateException;
    092
    093        /**
    094         * Return an instance to the pool.
    095         * By contract, <code>obj</code> <strong>must</strong> have been obtained
    096         * using {@link #borrowObject() borrowObject}
    097         * or a related method as defined in an implementation
    098         * or sub-interface.
    099         *
    100         * @param obj a {@link #borrowObject borrowed} instance to be returned.
    101         * @throws Exception
    102         */
    103        void returnObject(Object obj) throws Exception;
    104
    105        /**
    106         * <p>Invalidates an object from the pool.</p>
    107         *
    108         * <p>By contract, <code>obj</code> <strong>must</strong> have been obtained
    109         * using {@link #borrowObject borrowObject} or a related method as defined in
    110         * an implementation or sub-interface.</p>
    111         *
    112         * <p>This method should be used when an object that has been borrowed
    113         * is determined (due to an exception or other problem) to be invalid.</p>
    114         *
    115         * @param obj a {@link #borrowObject borrowed} instance to be disposed.
    116         * @throws Exception
    117         */
    118        void invalidateObject(Object obj) throws Exception;
    119
    120        /**
    121         * Create an object using the {@link PoolableObjectFactory factory} or other
    122         * implementation dependent mechanism, passivate it, and then place it in the idle object pool.
    123         * <code>addObject</code> is useful for "pre-loading" a pool with idle objects.
    124         * (Optional operation).
    125         *
    126         * @throws Exception when {@link PoolableObjectFactory#makeObject} fails.
    127         * @throws IllegalStateException after {@link #close} has been called on this pool.
    128         * @throws UnsupportedOperationException when this pool cannot add new idle objects.
    129         */
    130        void addObject() throws Exception, IllegalStateException, UnsupportedOperationException;
    131
    132        /**
    133         * Return the number of instances
    134         * currently idle in this pool (optional operation).
    135         * This may be considered an approximation of the number
    136         * of objects that can be {@link #borrowObject borrowed}
    137         * without creating any new instances.
    138         * Returns a negative value if this information is not available.
    139         *
    140         * @return the number of instances currently idle in this pool or a negative value if unsupported
    141         * @throws UnsupportedOperationException <strong>deprecated</strong>: if this implementation does not support the operation
    142         */
    143        int getNumIdle() throws UnsupportedOperationException;
    144
    145        /**
    146         * Return the number of instances
    147         * currently borrowed from this pool
    148         * (optional operation).
    149         * Returns a negative value if this information is not available.
    150         *
    151         * @return the number of instances currently borrowed from this pool or a negative value if unsupported
    152         * @throws UnsupportedOperationException <strong>deprecated</strong>: if this implementation does not support the operation
    153         */
    154        int getNumActive() throws UnsupportedOperationException;
    155
    156        /**
    157         * Clears any objects sitting idle in the pool, releasing any
    158         * associated resources (optional operation).
    159         * Idle objects cleared must be {@link PoolableObjectFactory#destroyObject(Object) destroyed}.
    160         *
    161         * @throws UnsupportedOperationException if this implementation does not support the operation
    162         */
    163        void clear() throws Exception, UnsupportedOperationException;
    164
    165        /**
    166         * Close this pool, and free any resources associated with it.
    167         * <p>
    168         * Calling {@link #addObject} or {@link #borrowObject} after invoking
    169         * this method on a pool will cause them to throw an
    170         * {@link IllegalStateException}.
    171         * </p>
    172         *
    173         * @throws Exception <strong>deprecated</strong>: implementations should silently fail if not all resources can be freed.
    174         */
    175        void close() throws Exception;
    176
    177        /**
    178         * Sets the {@link PoolableObjectFactory factory} this pool uses
    179         * to create new instances (optional operation). Trying to change
    180         * the <code>factory</code> after a pool has been used will frequently
    181         * throw an {@link UnsupportedOperationException}. It is up to the pool
    182         * implementation to determine when it is acceptable to call this method.
    183         *
    184         * @param factory the {@link PoolableObjectFactory} used to create new instances.
    185         * @throws IllegalStateException when the factory cannot be set at this time
    186         * @throws UnsupportedOperationException if this implementation does not support the operation
    187         * @deprecated to be removed in pool 2.0
    188         */
    189        void setFactory(PoolableObjectFactory factory) throws IllegalStateException, UnsupportedOperationException;
    190    }