Multiple readers for InputStream in Java

Question

I have an InputStream from which I\'m reading characters. I would like multiple readers to access this InputStream. It seems that a reasonable way to achieve this is to writ

Answer 1

Looking for a possible way to have an outputstream sending bytes to two or more different Inputstream, I found this forum. Unfortunately, the exact solution was directing to PipedOutputStream and PipedInputStream. So, I was declined to write a PipeOutputStream extension. Here it is. The example is written in the PipedOutputStream's "main" method.

/**
 * Extensao de {@link PipedOutputStream}, onde eh possivel conectar mais de um {@link PipedInputStream}
 */
public class PipedOutputStreamEx extends PipedOutputStream {

    /**
     * 
     */
    public PipedOutputStreamEx() {
        // TODO Auto-generated constructor stub
    }

    /* REMIND: identification of the read and write sides needs to be
       more sophisticated.  Either using thread groups (but what about
       pipes within a thread?) or using finalization (but it may be a
       long time until the next GC). */
    private PipedInputStreamEx[] sinks=null;

    public synchronized void connect(PipedInputStreamEx... pIns) throws IOException {
        for (PipedInputStreamEx snk : pIns) {
            if (snk == null) {
                throw new NullPointerException();
            } else if (sinks != null || snk.connected) {
                throw new IOException("Already connected");
            }
            snk.in = -1;
            snk.out = 0;
            snk.connected = true;
        }

        this.sinks = pIns;
    }


    /**
     * Writes the specified byte to the piped output stream. 
     * 

     * Implements the write method of OutputStream.
     *
     * @param      b   the byte to be written.
     * @exception IOException if the pipe is  broken,
     *      {@link #connect(java.io.PipedInputStream) unconnected},
     *      closed, or if an I/O error occurs.
     */
    public void write(int b)  throws IOException {
        if (this.sinks == null) {
            throw new IOException("Pipe(s) not connected");
        }
        for (PipedInputStreamEx sink : this.sinks) {
            sink.receive(b);
        }
    }

    /**
     * Writes len bytes from the specified byte array 
     * starting at offset off to this piped output stream. 
     * This method blocks until all the bytes are written to the output
     * stream.
     *
     * @param      b     the data.
     * @param      off   the start offset in the data.
     * @param      len   the number of bytes to write.
     * @exception IOException if the pipe is  broken,
     *          {@link #connect(java.io.PipedInputStream) unconnected},
     *      closed, or if an I/O error occurs.
     */
    public void write(byte b[], int off, int len) throws IOException {
        if (sinks == null) {
            throw new IOException("Pipe not connected");
        } else if (b == null) {
            throw new NullPointerException();
        } else if ((off < 0) || (off > b.length) || (len < 0) ||
                ((off + len) > b.length) || ((off + len) < 0)) {
            throw new IndexOutOfBoundsException();
        } else if (len == 0) {
            return;
        } 
        for (PipedInputStreamEx sink : this.sinks) {
            sink.receive(b, off, len);
        }
    }

    /**
     * Flushes this output stream and forces any buffered output bytes 
     * to be written out. 
     * This will notify any readers that bytes are waiting in the pipe.
     *
     * @exception IOException if an I/O error occurs.
     */
    public synchronized void flush() throws IOException {
        if (sinks != null) {
            for (PipedInputStreamEx sink : this.sinks) {
                synchronized (sink) {
                    sink.notifyAll();
                }
            }
        }
    }

    /**
     * Closes this piped output stream and releases any system resources 
     * associated with this stream. This stream may no longer be used for 
     * writing bytes.
     *
     * @exception  IOException  if an I/O error occurs.
     */
    public void close()  throws IOException {
        if (sinks != null) {
            for (PipedInputStreamEx sink : this.sinks) {
                sink.receivedLast();
            }
        }
    }


    /**
     * Teste desta extensao de {@link PipedOutputStream}
     * @param args
     * @throws InterruptedException 
     * @throws IOException 
     */
    public static void main(String[] args) throws InterruptedException, IOException {
        final PipedOutputStreamEx pOut = new PipedOutputStreamEx();
        final PipedInputStreamEx pInHash = new PipedInputStreamEx();
        final PipedInputStreamEx pInConsole = new PipedInputStreamEx();

        pOut.connect(pInHash, pInConsole);

        Thread escreve = new Thread("Escrevendo") {
            @Override
            public void run() {
                String[] paraGravar = new String[]{
                        "linha1 0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\n"
                        , "linha2 0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\n"
                        , "linha3 0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\n"
                        , "linha4 0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\n"
                        , "linha5 0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\n"
                        , "linha6 0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\n"
                        , "linha7 0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\n"
                        , "linha8 0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\n"
                        , "linha9 0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\n"
                        , "linha10 0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\n"
                        , "linha11 0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\n"
                        , "linha12 0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\n"
                        , "linha13 0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\n"
                        , "linha14 0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\n"
                        , "linha15 0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\n"
                        , "linha16 0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\n"
                        , "linha17 0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\n"
                        , "linha18 0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\n"
                        , "linha19 0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\n"
                        , "linha20 0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789\n"
                };
                for (String s :paraGravar) {
                    try {
                        pOut.write(s.getBytes("ISO-8859-1") );
                        Thread.sleep(100);
                    } catch (Exception e) {
                        throw new RuntimeException(e);
                    }
                }
                try {
                    pOut.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }   
        };

        Thread le1 = new Thread("Le1 - hash") {
            @Override
            public void run() {
                try {
                    System.out.println("HASH: "+HashUtil.getHashCRC(pInHash,true));                         
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        };

        Thread le2 = new Thread("Le2 - escreve no console") {
            @Override
            public void run() {
                BufferedReader bIn = new BufferedReader(new InputStreamReader(pInConsole));
                String s;
                try {
                    while ( (s=bIn.readLine())!=null) {
                        Thread.sleep(700); //teste simulando o um leitor lento...
                        System.out.println(s);
                    }
                } catch (IOException e) {
                    throw new RuntimeException(e);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        };


        escreve.start();
        le1.start();
        le2.start();

        escreve.join();
        le1.join();
        le2.join();

        pInHash.close();
        pInConsole.close();
    }
}

Here is the PipedInputStreamEx code. Unfortunately, I had to copy all JDK code, to have access to "connected", "in" and "out" properties.

/**
 * Extensao de {@link PipedInputStream}, que permite conetar mais de um destes no {@link PipedOutputStream}
 * Como a classe ancestral possui propriedades 'package friend', tivemos que copiar o codigo herdado :/
 */
public class PipedInputStreamEx extends PipedInputStream {

    @Override
    public void connect(PipedOutputStream src) throws IOException {
        throw new IOException("conecte usando PipedOutputStream.connect()");
    }

//----------------------------------------------------------------------------------------------------------
//----------------------------------------------------------------------------------------------------------
//----------------------------------------------------------------------------------------------------------
//--------- INICIO codigo da classe herdada (alguns metodos comentados...)----------------------------------
//----------------------------------------------------------------------------------------------------------

    boolean closedByWriter = false;
    volatile boolean closedByReader = false;
    boolean connected = false;

    /* REMIND: identification of the read and write sides needs to be
       more sophisticated.  Either using thread groups (but what about
       pipes within a thread?) or using finalization (but it may be a
       long time until the next GC). */
    Thread readSide;
    Thread writeSide;

    private static final int DEFAULT_PIPE_SIZE = 1024;

    /**
     * The default size of the pipe's circular input buffer.
     * @since   JDK1.1
     */
    // This used to be a constant before the pipe size was allowed
    // to change. This field will continue to be maintained
    // for backward compatibility. 
    protected static final int PIPE_SIZE = DEFAULT_PIPE_SIZE;

    /**
     * The circular buffer into which incoming data is placed.
     * @since   JDK1.1
     */
    protected byte buffer[];

    /**
     * The index of the position in the circular buffer at which the
     * next byte of data will be stored when received from the connected
     * piped output stream. in<0 implies the buffer is empty,
     * in==out implies the buffer is full
     * @since   JDK1.1
     */
    protected int in = -1;

    /**
     * The index of the position in the circular buffer at which the next
     * byte of data will be read by this piped input stream.
     * @since   JDK1.1
     */
    protected int out = 0;

//    /**
//     * Creates a PipedInputStream so
//     * that it is connected to the piped output
//     * stream src. Data bytes written
//     * to src will then be  available
//     * as input from this stream.
//     *
//     * @param      src   the stream to connect to.
//     * @exception  IOException  if an I/O error occurs.
//     */
//    public PipedInputStream(PipedOutputStream src) throws IOException {
//        this(src, DEFAULT_PIPE_SIZE);
//    }
//
//    /**
//     * Creates a PipedInputStream so that it is
//     * connected to the piped output stream
//     * src and uses the specified pipe size for
//     * the pipe's buffer.
//     * Data bytes written to src will then
//     * be available as input from this stream.
//     *
//     * @param      src   the stream to connect to.
//     * @param      pipeSize the size of the pipe's buffer.
//     * @exception  IOException  if an I/O error occurs.
//     * @exception  IllegalArgumentException if pipeSize <= 0.
//     * @since    1.6
//     */
//    public PipedInputStream(PipedOutputStream src, int pipeSize)
//            throws IOException {
//   initPipe(pipeSize);
//   connect(src);
//    }

    /**
     * Creates a PipedInputStream so
     * that it is not yet {@linkplain #connect(java.io.PipedOutputStream)
     * connected}.
     * It must be {@linkplain java.io.PipedOutputStream#connect(
     * java.io.PipedInputStream) connected} to a
     * PipedOutputStream before being used.
     */
    public PipedInputStreamEx() {
    initPipe(DEFAULT_PIPE_SIZE);
    }

    /**
     * Creates a PipedInputStream so that it is not yet
     * {@linkplain #connect(java.io.PipedOutputStream) connected} and
     * uses the specified pipe size for the pipe's buffer.
     * It must be {@linkplain java.io.PipedOutputStream#connect(
     * java.io.PipedInputStream)
     * connected} to a PipedOutputStream before being used.
     *
     * @param      pipeSize the size of the pipe's buffer.
     * @exception  IllegalArgumentException if pipeSize <= 0.
     * @since      1.6
     */
    public PipedInputStreamEx(int pipeSize) {
    initPipe(pipeSize);
    }

    private void initPipe(int pipeSize) {
         if (pipeSize <= 0) {
            throw new IllegalArgumentException("Pipe Size <= 0");
         }
         buffer = new byte[pipeSize];
    }

//    /**
//     * Causes this piped input stream to be connected
//     * to the piped  output stream src.
//     * If this object is already connected to some
//     * other piped output  stream, an IOException
//     * is thrown.
//     * 

//     * If src is an
//     * unconnected piped output stream and snk
//     * is an unconnected piped input stream, they
//     * may be connected by either the call:
//     * 

//     * 
snk.connect(src) 
//     * 

//     * or the call:
//     * 

//     * 
src.connect(snk) 
//     * 

//     * The two
//     * calls have the same effect.
//     *
//     * @param      src   The piped output stream to connect to.
//     * @exception  IOException  if an I/O error occurs.
//     */
//    public void connect(PipedOutputStream src) throws IOException {
//  src.connect(this);
//    }

    /**
     * Receives a byte of data.  This method will block if no input is
     * available.
     * @param b the byte being received
     * @exception IOException If the pipe is  broken,
     *      {@link #connect(java.io.PipedOutputStream) unconnected},
     *      closed, or if an I/O error occurs.
     * @since     JDK1.1
     */
    protected synchronized void receive(int b) throws IOException {
        checkStateForReceive();
        writeSide = Thread.currentThread();
        if (in == out)
            awaitSpace();
    if (in < 0) {
        in = 0;
        out = 0;
    }
    buffer[in++] = (byte)(b & 0xFF);
    if (in >= buffer.length) {
        in = 0;
    }
    }

    /**
     * Receives data into an array of bytes.  This method will
     * block until some input is available.
     * @param b the buffer into which the data is received
     * @param off the start offset of the data
     * @param len the maximum number of bytes received
     * @exception IOException If the pipe is  broken,
     *       {@link #connect(java.io.PipedOutputStream) unconnected},
     *       closed,or if an I/O error occurs.
     */
    synchronized void receive(byte b[], int off, int len)  throws IOException {
        checkStateForReceive();
        writeSide = Thread.currentThread();
        int bytesToTransfer = len;
        while (bytesToTransfer > 0) {
            if (in == out)
                awaitSpace();
            int nextTransferAmount = 0;
            if (out < in) {
                nextTransferAmount = buffer.length - in;
            } else if (in < out) {
                if (in == -1) {
                    in = out = 0;
                    nextTransferAmount = buffer.length - in;
                } else {
                    nextTransferAmount = out - in;
                }
            }
            if (nextTransferAmount > bytesToTransfer)
                nextTransferAmount = bytesToTransfer;
            assert(nextTransferAmount > 0);
            System.arraycopy(b, off, buffer, in, nextTransferAmount);
            bytesToTransfer -= nextTransferAmount;
            off += nextTransferAmount;
            in += nextTransferAmount;
            if (in >= buffer.length) {
                in = 0;
            }
        }
    }

    private void checkStateForReceive() throws IOException {
        if (!connected) {
            throw new IOException("Pipe not connected");
        } else if (closedByWriter || closedByReader) {
        throw new IOException("Pipe closed");
    } else if (readSide != null && !readSide.isAlive()) {
            throw new IOException("Read end dead");
        }
    }

    private void awaitSpace() throws IOException {
    while (in == out) {
        checkStateForReceive();

        /* full: kick any waiting readers */
        notifyAll();
        try {
            wait(1000);
        } catch (InterruptedException ex) {
        throw new java.io.InterruptedIOException();
        }
    }
    }

    /**
     * Notifies all waiting threads that the last byte of data has been
     * received.
     */
    synchronized void receivedLast() {
    closedByWriter = true;
    notifyAll();
    }

    /**
     * Reads the next byte of data from this piped input stream. The
     * value byte is returned as an int in the range
     * 0 to 255. 
     * This method blocks until input data is available, the end of the
     * stream is detected, or an exception is thrown.
     *
     * @return     the next byte of data, or -1 if the end of the
     *             stream is reached.
     * @exception  IOException  if the pipe is
     *       {@link #connect(java.io.PipedOutputStream) unconnected},
     *        broken, closed,
     *       or if an I/O error occurs.
     */
    public synchronized int read()  throws IOException {
        if (!connected) {
            throw new IOException("Pipe not connected");
        } else if (closedByReader) {
        throw new IOException("Pipe closed");
    } else if (writeSide != null && !writeSide.isAlive()
                   && !closedByWriter && (in < 0)) {
            throw new IOException("Write end dead");
    }

        readSide = Thread.currentThread();
    int trials = 2;
    while (in < 0) {
        if (closedByWriter) {
        /* closed by writer, return EOF */
        return -1;
        }
        if ((writeSide != null) && (!writeSide.isAlive()) && (--trials < 0)) {
        throw new IOException("Pipe broken");
        }
            /* might be a writer waiting */
        notifyAll();
        try {
            wait(1000);
        } catch (InterruptedException ex) {
        throw new java.io.InterruptedIOException();
        }
    }
    int ret = buffer[out++] & 0xFF;
    if (out >= buffer.length) {
        out = 0;
    }
    if (in == out) {
            /* now empty */
        in = -1;
    }

    return ret;
    }

    /**
     * Reads up to len bytes of data from this piped input
     * stream into an array of bytes. Less than len bytes
     * will be read if the end of the data stream is reached or if 
     * len exceeds the pipe's buffer size.
     * If len  is zero, then no bytes are read and 0 is returned; 
     * otherwise, the method blocks until at least 1 byte of input is 
     * available, end of the stream has been detected, or an exception is
     * thrown.
     *
     * @param      b     the buffer into which the data is read.
     * @param      off   the start offset in the destination array b
     * @param      len   the maximum number of bytes read.
     * @return     the total number of bytes read into the buffer, or
     *             -1 if there is no more data because the end of
     *             the stream has been reached.
     * @exception  NullPointerException If b is null.
     * @exception  IndexOutOfBoundsException If off is negative, 
     * len is negative, or len is greater than 
     * b.length - off
     * @exception  IOException if the pipe is  broken,
     *       {@link #connect(java.io.PipedOutputStream) unconnected},
     *       closed, or if an I/O error occurs.
     */
    public synchronized int read(byte b[], int off, int len)  throws IOException {
    if (b == null) {
        throw new NullPointerException();
    } else if (off < 0 || len < 0 || len > b.length - off) {
        throw new IndexOutOfBoundsException();
    } else if (len == 0) {
        return 0;
    }

        /* possibly wait on the first character */
    int c = read();
    if (c < 0) {
        return -1;
    }
    b[off] = (byte) c;
    int rlen = 1;
    while ((in >= 0) && (len > 1)) {

        int available; 

        if (in > out) {
        available = Math.min((buffer.length - out), (in - out));
        } else {
        available = buffer.length - out;
        }

        // A byte is read beforehand outside the loop
        if (available > (len - 1)) {
        available = len - 1;
        }
        System.arraycopy(buffer, out, b, off + rlen, available);
        out += available;
        rlen += available; 
        len -= available;

        if (out >= buffer.length) {
        out = 0;
        }
        if (in == out) {
                /* now empty */
        in = -1;
        }
    }
    return rlen;
    }

    /**
     * Returns the number of bytes that can be read from this input
     * stream without blocking.
     *
     * @return the number of bytes that can be read from this input stream
     *         without blocking, or {@code 0} if this input stream has been
     *         closed by invoking its {@link #close()} method, or if the pipe
     *         is {@link #connect(java.io.PipedOutputStream) unconnected}, or
     *       broken.
     *
     * @exception  IOException  if an I/O error occurs.
     * @since   JDK1.0.2
     */
    public synchronized int available() throws IOException {
    if(in < 0)
        return 0;
    else if(in == out)
        return buffer.length;
    else if (in > out)
        return in - out;
    else
        return in + buffer.length - out;
    }

    /**
     * Closes this piped input stream and releases any system resources
     * associated with the stream.
     *
     * @exception  IOException  if an I/O error occurs.
     */
    public void close()  throws IOException {
    closedByReader = true;
        synchronized (this) {
            in = -1;
        }
    }

//----------------------------------------------------------------------------------------------------------
//--------- FIM codigo da classe herdada -------------------------------------------------------------------
//----------------------------------------------------------------------------------------------------------


}