    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 *      https://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 */
    017package org.apache.commons.pool2;
    018
    019/**
    020 * A simple base implementation of {@link ObjectPool}.
    021 * Optional operations are implemented to either do nothing, return a value
    022 * indicating it is unsupported or throw {@link UnsupportedOperationException}.
    023 * <p>
    024 * This class is intended to be thread-safe.
    025 * </p>
    026 *
    027 * @param <T> Type of element pooled in this pool.
    028 * @since 2.0
    029 */
    030public abstract class BaseObjectPool<T> extends BaseObject implements ObjectPool<T> {
    031
    032    private volatile boolean closed;
    033
    034    /**
    035     * Constructs a new instance.
    036     */
    037    public BaseObjectPool() {
    038        // empty
    039    }
    040
    041    /**
    042     * Not supported in this base implementation. Subclasses should override
    043     * this behavior.
    044     *
    045     * @throws UnsupportedOperationException if the pool does not implement this
    046     *          method
    047     */
    048    @Override
    049    public void addObject() throws Exception {
    050        throw new UnsupportedOperationException();
    051    }
    052
    053    /**
    054     * Throws an {@code IllegalStateException} when this pool has been
    055     * closed.
    056     *
    057     * @throws IllegalStateException when this pool has been closed.
    058     * @see #isClosed()
    059     */
    060    protected final void assertOpen() throws IllegalStateException {
    061        if (isClosed()) {
    062            throw new IllegalStateException("Pool not open");
    063        }
    064    }
    065
    066    @Override
    067    public abstract T borrowObject() throws Exception;
    068
    069    /**
    070     * Not supported in this base implementation.
    071     *
    072     * @throws UnsupportedOperationException if the pool does not implement this
    073     *          method
    074     */
    075    @Override
    076    public void clear() throws Exception {
    077        throw new UnsupportedOperationException();
    078    }
    079
    080    /**
    081     * {@inheritDoc}
    082     * <p>
    083     * This affects the behavior of {@code isClosed} and
    084     * {@code assertOpen}.
    085     * </p>
    086     */
    087    @Override
    088    public void close() {
    089        closed = true;
    090    }
    091
    092    /**
    093     * Not supported in this base implementation.
    094     *
    095     * @return a negative value.
    096     */
    097    @Override
    098    public int getNumActive() {
    099        return -1;
    100    }
    101
    102    /**
    103     * Not supported in this base implementation.
    104     *
    105     * @return a negative value.
    106     */
    107    @Override
    108    public int getNumIdle() {
    109        return -1;
    110    }
    111
    112    @Override
    113    public abstract void invalidateObject(T obj) throws Exception;
    114
    115    /**
    116     * Has this pool instance been closed.
    117     *
    118     * @return {@code true} when this pool has been closed.
    119     */
    120    public final boolean isClosed() {
    121        return closed;
    122    }
    123
    124    @Override
    125    public abstract void returnObject(T obj) throws Exception;
    126
    127    @Override
    128    protected void toStringAppendFields(final StringBuilder builder) {
    129        builder.append("closed=");
    130        builder.append(closed);
    131    }
    132}