    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 */
    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 *
    029 *
    030 * @since 2.0
    031 */
    032public abstract class BaseObjectPool<T> extends BaseObject implements ObjectPool<T> {
    033
    034    private volatile boolean closed;
    035
    036    /**
    037     * Not supported in this base implementation. Subclasses should override
    038     * this behavior.
    039     *
    040     * @throws UnsupportedOperationException if the pool does not implement this
    041     *          method
    042     */
    043    @Override
    044    public void addObject() throws Exception {
    045        throw new UnsupportedOperationException();
    046    }
    047
    048    /**
    049     * Throws an {@code IllegalStateException} when this pool has been
    050     * closed.
    051     *
    052     * @throws IllegalStateException when this pool has been closed.
    053     *
    054     * @see #isClosed()
    055     */
    056    protected final void assertOpen() throws IllegalStateException {
    057        if (isClosed()) {
    058            throw new IllegalStateException("Pool not open");
    059        }
    060    }
    061
    062    @Override
    063    public abstract T borrowObject() throws Exception;
    064
    065    /**
    066     * Not supported in this base implementation.
    067     *
    068     * @throws UnsupportedOperationException if the pool does not implement this
    069     *          method
    070     */
    071    @Override
    072    public void clear() throws Exception {
    073        throw new UnsupportedOperationException();
    074    }
    075
    076    /**
    077     * {@inheritDoc}
    078     * <p>
    079     * This affects the behavior of {@code isClosed} and
    080     * {@code assertOpen}.
    081     * </p>
    082     */
    083    @Override
    084    public void close() {
    085        closed = true;
    086    }
    087
    088    /**
    089     * Not supported in this base implementation.
    090     *
    091     * @return a negative value.
    092     */
    093    @Override
    094    public int getNumActive() {
    095        return -1;
    096    }
    097
    098    /**
    099     * Not supported in this base implementation.
    100     *
    101     * @return a negative value.
    102     */
    103    @Override
    104    public int getNumIdle() {
    105        return -1;
    106    }
    107
    108    @Override
    109    public abstract void invalidateObject(T obj) throws Exception;
    110
    111    /**
    112     * Has this pool instance been closed.
    113     *
    114     * @return {@code true} when this pool has been closed.
    115     */
    116    public final boolean isClosed() {
    117        return closed;
    118    }
    119
    120    @Override
    121    public abstract void returnObject(T obj) throws Exception;
    122
    123    @Override
    124    protected void toStringAppendFields(final StringBuilder builder) {
    125        builder.append("closed=");
    126        builder.append(closed);
    127    }
    128}