RFR [9] Add blocking bulk read to java.io.InputStream

Chris Hegarty chris.hegarty at oracle.com
Thu Apr 23 09:01:38 UTC 2015

A while back when we added the long overdue java.io.InputStream.transferTo method, there was support for adding a blocking bulk read operation. This has been sitting in a branch in the sandbox since then. I would like to revive it with the intention of bringing it into 9. The motivation for this addition is provide library support for a common pattern found when reading from input streams.

 * Reads some bytes from the input stream into the given byte array. This
 * method blocks until {@code len} bytes of input data have been read, or
 * end of stream is detected. The number of bytes actually read, possibly
 * zero, is returned. This method does not close the input stream.
 * <p> In the case where end of stream is reached before {@code len} bytes
 * have been read, then the actual number of bytes read will be returned.
 * When this stream reaches end of stream, further invocations of this
 * method will return zero.
 * <p> If {@code len} is zero, then no bytes are read and {@code 0} is
 * returned; otherwise, there is an attempt to read up to {@code len} bytes.
 * <p> The first byte read is stored into element {@code b[off]}, the next
 * one in to {@code b[off+1]}, and so on. The number of bytes read is, at
 * most, equal to {@code len}. Let <i>k</i> be the number of bytes actually
 * read; these bytes will be stored in elements {@code b[off]} through
 * {@code b[off+}<i>k</i>{@code -1]}, leaving elements {@code b[off+}<i>k</i>
 * {@code ]} through {@code b[off+len-1]} unaffected.
 * <p> In every case, elements {@code b[0]} through {@code b[off]} and
 * elements{@code b[off+len]} through {@code b[b.length-1]} are unaffected.
 * <p> The behavior for the case where the input stream is <i>asynchronously
 * closed</i>, or the thread interrupted during the read, is highly input
 * stream specific, and therefore not specified.
 * <p> If an I/O error occurs reading from the input stream, then it may do
 * so after some bytes have been read. Consequently the input stream may be
 * in an inconsistent state. It is strongly recommended that the stream be
 * promptly closed if an I/O error occurs.
 * @param  b the buffer into which the data is read
 * @param  off the start offset in {@code b} at which the data is written
 * @param  len the maximum number of bytes to read
 * @return the actual number of bytes read into the buffer
 * @throws IOException if an I/O error occurs
 * @throws NullPointerException if {@code b} is {@code null}
 * @throws IndexOutOfBoundsException If {@code off} is negative, {@code len}
 *                is negative, or {@code len} is greater than {@code b.length - off}
 * @since 1.9
public int readBytes(byte[] b, int off, int len) throws IOException {
    if (off < 0 || len < 0 || len > b.length - off)
        throw new IndexOutOfBoundsException();
    int n = 0;
    while (n < len) {
        int count = read(b, off + n, len - n);
        if (count < 0)
        n += count;
    return n;


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