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