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 *
026 * @param <T> Type of element pooled in this pool.
027 *
028 * @since 2.0
029 */
030public abstract class BaseObjectPool<T> extends BaseObject implements ObjectPool<T> {
031
032    @Override
033    public abstract T borrowObject() throws Exception;
034
035    @Override
036    public abstract void returnObject(T obj) throws Exception;
037
038    @Override
039    public abstract void invalidateObject(T obj) throws Exception;
040
041    /**
042     * Not supported in this base implementation.
043     *
044     * @return a negative value.
045     */
046    @Override
047    public int getNumIdle() {
048        return -1;
049    }
050
051    /**
052     * Not supported in this base implementation.
053     *
054     * @return a negative value.
055     */
056    @Override
057    public int getNumActive() {
058        return -1;
059    }
060
061    /**
062     * Not supported in this base implementation.
063     *
064     * @throws UnsupportedOperationException if the pool does not implement this
065     *          method
066     */
067    @Override
068    public void clear() throws Exception, UnsupportedOperationException {
069        throw new UnsupportedOperationException();
070    }
071
072    /**
073     * Not supported in this base implementation. Subclasses should override
074     * this behavior.
075     *
076     * @throws UnsupportedOperationException if the pool does not implement this
077     *          method
078     */
079    @Override
080    public void addObject() throws Exception, UnsupportedOperationException {
081        throw new UnsupportedOperationException();
082    }
083
084    /**
085     * {@inheritDoc}
086     * <p>
087     * This affects the behavior of <code>isClosed</code> and
088     * <code>assertOpen</code>.
089     * </p>
090     */
091    @Override
092    public void close() {
093        closed = true;
094    }
095
096    /**
097     * Has this pool instance been closed.
098     *
099     * @return <code>true</code> when this pool has been closed.
100     */
101    public final boolean isClosed() {
102        return closed;
103    }
104
105    /**
106     * Throws an <code>IllegalStateException</code> when this pool has been
107     * closed.
108     *
109     * @throws IllegalStateException when this pool has been closed.
110     *
111     * @see #isClosed()
112     */
113    protected final void assertOpen() throws IllegalStateException {
114        if (isClosed()) {
115            throw new IllegalStateException("Pool not open");
116        }
117    }
118
119    private volatile boolean closed = false;
120
121    @Override
122    protected void toStringAppendFields(final StringBuilder builder) {
123        builder.append("closed=");
124        builder.append(closed);
125    }
126}