    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.io.input;
    018
    019import static org.apache.commons.io.IOUtils.EOF;
    020
    021import org.apache.commons.io.output.QueueOutputStream;
    022
    023import java.io.InputStream;
    024import java.io.PipedInputStream;
    025import java.io.PipedOutputStream;
    026import java.util.Objects;
    027import java.util.concurrent.BlockingQueue;
    028import java.util.concurrent.LinkedBlockingQueue;
    029
    030/**
    031 * Simple alternative to JDK {@link java.io.PipedInputStream}; queue input stream provides what's written in queue
    032 * output stream.
    033 *
    034 * <p>
    035 * Example usage:
    036 * </p>
    037 * <pre>
    038 * QueueInputStream inputStream = new QueueInputStream();
    039 * QueueOutputStream outputStream = inputStream.newQueueOutputStream();
    040 *
    041 * outputStream.write("hello world".getBytes(UTF_8));
    042 * inputStream.read();
    043 * </pre>
    044 * <p>
    045 * Unlike JDK {@link PipedInputStream} and {@link PipedOutputStream}, queue input/output streams may be used safely in a
    046 * single thread or multiple threads. Also, unlike JDK classes, no special meaning is attached to initial or current
    047 * thread. Instances can be used longer after initial threads exited.
    048 * </p>
    049 * <p>
    050 * Closing a {@code QueueInputStream} has no effect. The methods in this class can be called after the stream has been
    051 * closed without generating an {@code IOException}.
    052 * </p>
    053 *
    054 * @see QueueOutputStream
    055 * @since 2.9.0
    056 */
    057public class QueueInputStream extends InputStream {
    058
    059    private final BlockingQueue<Integer> blockingQueue;
    060
    061    /**
    062     * Constructs a new instance with no limit to its internal buffer size.
    063     */
    064    public QueueInputStream() {
    065        this(new LinkedBlockingQueue<>());
    066    }
    067
    068    /**
    069     * Constructs a new instance with given buffer
    070     *
    071     * @param blockingQueue backing queue for the stream
    072     */
    073    public QueueInputStream(final BlockingQueue<Integer> blockingQueue) {
    074        this.blockingQueue = Objects.requireNonNull(blockingQueue, "blockingQueue");
    075    }
    076
    077    /**
    078     * Creates a new QueueOutputStream instance connected to this. Writes to the output stream will be visible to this
    079     * input stream.
    080     *
    081     * @return QueueOutputStream connected to this stream
    082     */
    083    public QueueOutputStream newQueueOutputStream() {
    084        return new QueueOutputStream(blockingQueue);
    085    }
    086
    087    /**
    088     * Reads and returns a single byte.
    089     *
    090     * @return either the byte read or {@code -1} if the end of the stream has been reached
    091     */
    092    @Override
    093    public int read() {
    094        final Integer value = blockingQueue.poll();
    095        return value == null ? EOF : ((0xFF) & value);
    096    }
    097
    098}