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Java example source code file (EofSensorInputStream.java)

This example source code file (EofSensorInputStream.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java tags/keywords

attempted, connectionreleasetrigger, eofsensorinputstream, eofsensorwatcher, illegalargumentexception, inputstream, io, ioexception, notthreadsafe, override, wrapped

The EofSensorInputStream.java example source code

/*
 * ====================================================================
 *
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */

package org.apache.http.conn;

import java.io.InputStream;
import java.io.IOException;

import org.apache.http.annotation.NotThreadSafe;

/**
 * A stream wrapper that triggers actions on {@link #close close()} and EOF.
 * Primarily used to auto-release an underlying
 * {@link ManagedClientConnection connection}
 * when the response body is consumed or no longer needed.
 * <p>
 * This class is based on <code>AutoCloseInputStream in HttpClient 3.1,
 * but has notable differences. It does not allow mark/reset, distinguishes
 * different kinds of event, and does not always close the underlying stream
 * on EOF. That decision is left to the {@link EofSensorWatcher watcher}.
 *
 * @see EofSensorWatcher
 *
 * @since 4.0
 */
// don't use FilterInputStream as the base class, we'd have to
// override markSupported(), mark(), and reset() to disable them
@NotThreadSafe
public class EofSensorInputStream extends InputStream implements ConnectionReleaseTrigger {

    /**
     * The wrapped input stream, while accessible.
     * The value changes to <code>null when the wrapped stream
     * becomes inaccessible.
     */
    protected InputStream wrappedStream;

    /**
     * Indicates whether this stream itself is closed.
     * If it isn't, but {@link #wrappedStream wrappedStream}
     * is <code>null, we're running in EOF mode.
     * All read operations will indicate EOF without accessing 
     * the underlying stream. After closing this stream, read
     * operations will trigger an {@link IOException IOException}.
     *
     * @see #isReadAllowed isReadAllowed
     */
    private boolean selfClosed;

    /** The watcher to be notified, if any. */
    private final EofSensorWatcher eofWatcher;

    /**
     * Creates a new EOF sensor.
     * If no watcher is passed, the underlying stream will simply be
     * closed when EOF is detected or {@link #close close} is called.
     * Otherwise, the watcher decides whether the underlying stream
     * should be closed before detaching from it.
     *
     * @param in        the wrapped stream
     * @param watcher   the watcher for events, or <code>null for
     *                  auto-close behavior without notification
     */
    public EofSensorInputStream(final InputStream in,
                                final EofSensorWatcher watcher) {
        if (in == null) {
            throw new IllegalArgumentException
                ("Wrapped stream may not be null.");
        }

        wrappedStream = in;
        selfClosed = false;
        eofWatcher = watcher;
    }

    /**
     * Checks whether the underlying stream can be read from.
     *
     * @return  <code>true if the underlying stream is accessible,
     *          <code>false if this stream is in EOF mode and
     *          detached from the underlying stream
     *
     * @throws IOException      if this stream is already closed
     */
    protected boolean isReadAllowed() throws IOException {
        if (selfClosed) {
            throw new IOException("Attempted read on closed stream.");
        }
        return (wrappedStream != null);
    }

    @Override
    public int read() throws IOException {
        int l = -1;

        if (isReadAllowed()) {
            try {
                l = wrappedStream.read();
                checkEOF(l);
            } catch (IOException ex) {
                checkAbort();
                throw ex;
            }
        }

        return l;
    }

    @Override
    public int read(byte[] b, int off, int len) throws IOException {
        int l = -1;

        if (isReadAllowed()) {
            try {
                l = wrappedStream.read(b,  off,  len);
                checkEOF(l);
            } catch (IOException ex) {
                checkAbort();
                throw ex;
            }
        }

        return l;
    }

    @Override
    public int read(byte[] b) throws IOException {
        int l = -1;

        if (isReadAllowed()) {
            try {
                l = wrappedStream.read(b);
                checkEOF(l);
            } catch (IOException ex) {
                checkAbort();
                throw ex;
            }
        }
        return l;
    }

    @Override
    public int available() throws IOException {
        int a = 0; // not -1

        if (isReadAllowed()) {
            try {
                a = wrappedStream.available();
                // no checkEOF() here, available() can't trigger EOF
            } catch (IOException ex) {
                checkAbort();
                throw ex;
            }
        }

        return a;
    }

    @Override
    public void close() throws IOException {
        // tolerate multiple calls to close()
        selfClosed = true;
        checkClose();
    }

    /**
     * Detects EOF and notifies the watcher.
     * This method should only be called while the underlying stream is
     * still accessible. Use {@link #isReadAllowed isReadAllowed} to
     * check that condition.
     * <br/>
     * If EOF is detected, the watcher will be notified and this stream
     * is detached from the underlying stream. This prevents multiple
     * notifications from this stream.
     *
     * @param eof       the result of the calling read operation.
     *                  A negative value indicates that EOF is reached.
     *
     * @throws IOException
     *          in case of an IO problem on closing the underlying stream
     */
    protected void checkEOF(int eof) throws IOException {

        if ((wrappedStream != null) && (eof < 0)) {
            try {
                boolean scws = true; // should close wrapped stream?
                if (eofWatcher != null)
                    scws = eofWatcher.eofDetected(wrappedStream);
                if (scws)
                    wrappedStream.close();
            } finally {
                wrappedStream = null;
            }
        }
    }

    /**
     * Detects stream close and notifies the watcher.
     * There's not much to detect since this is called by {@link #close close}.
     * The watcher will only be notified if this stream is closed
     * for the first time and before EOF has been detected.
     * This stream will be detached from the underlying stream to prevent
     * multiple notifications to the watcher.
     *
     * @throws IOException
     *          in case of an IO problem on closing the underlying stream
     */
    protected void checkClose() throws IOException {

        if (wrappedStream != null) {
            try {
                boolean scws = true; // should close wrapped stream?
                if (eofWatcher != null)
                    scws = eofWatcher.streamClosed(wrappedStream);
                if (scws)
                    wrappedStream.close();
            } finally {
                wrappedStream = null;
            }
        }
    }

    /**
     * Detects stream abort and notifies the watcher.
     * There's not much to detect since this is called by
     * {@link #abortConnection abortConnection}.
     * The watcher will only be notified if this stream is aborted
     * for the first time and before EOF has been detected or the
     * stream has been {@link #close closed} gracefully.
     * This stream will be detached from the underlying stream to prevent
     * multiple notifications to the watcher.
     *
     * @throws IOException
     *          in case of an IO problem on closing the underlying stream
     */
    protected void checkAbort() throws IOException {

        if (wrappedStream != null) {
            try {
                boolean scws = true; // should close wrapped stream?
                if (eofWatcher != null)
                    scws = eofWatcher.streamAbort(wrappedStream);
                if (scws)
                    wrappedStream.close();
            } finally {
                wrappedStream = null;
            }
        }
    }

    /**
     * Same as {@link #close close()}.
     */
    public void releaseConnection() throws IOException {
        close();
    }

    /**
     * Aborts this stream.
     * This is a special version of {@link #close close()} which prevents
     * re-use of the underlying connection, if any. Calling this method
     * indicates that there should be no attempt to read until the end of
     * the stream.
     */
    public void abortConnection() throws IOException {
        // tolerate multiple calls
        selfClosed = true;
        checkAbort();
    }

}

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