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