documentinputstream.java

Office格式转换代码

     * is returned as an integer. The definition of this method in
     * java.io.InputStream allows this method to block, but it won't.
     * <p>
     * If b is null, a NullPointerException is thrown. If the length
     * of b is zero, then no bytes are read and 0 is returned;
     * otherwise, there is an attempt to read at least one byte. If no
     * byte is available because the stream is at end of file, the
     * value -1 is returned; otherwise, at least one byte is read and
     * stored into b.
     * <p>
     * The first byte read is stored into element b[0], the next one
     * into b[1], and so on. The number of bytes read is, at most,
     * equal to the length of b. Let k be the number of bytes actually
     * read; these bytes will be stored in elements b[0] through
     * b[k-1], leaving elements b[k] through b[b.length-1] unaffected.
     * <p>
     * If the first byte cannot be read for any reason other than end
     * of file, then an IOException is thrown. In particular, an
     * IOException is thrown if the input stream has been closed.
     * <p>
     * The read(b) method for class InputStream has the same effect as:
     * <p>
     * <code>read(b, 0, b.length)</code>
     *
     * @param b the buffer into which the data is 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 IOException
     * @exception NullPointerException
     */

    public int read(final byte [] b)
        throws IOException, NullPointerException
    {
        return read(b, 0, b.length);
    }

    /**
     * Reads up to len bytes of data from the input stream into an
     * array of bytes. An attempt is made to read as many as len
     * bytes, but a smaller number may be read, possibly zero. The
     * number of bytes actually read is returned as an integer.
     * <p>
     * The definition of this method in java.io.InputStream allows it
     * to block, but it won't.
     * <p>
     * If b is null, a NullPointerException is thrown.
     * <p>
     * If off is negative, or len is negative, or off+len is greater
     * than the length of the array b, then an
     * IndexOutOfBoundsException is thrown.
     * <p>
     * If len is zero, then no bytes are read and 0 is returned;
     * otherwise, there is an attempt to read at least one byte. If no
     * byte is available because the stream is at end of file, the
     * value -1 is returned; otherwise, at least one byte is read and
     * stored into b.
     * <p>
     * The first byte read is stored into element b[off], the next one
     * into b[off+1], and so on. The number of bytes read is, at most,
     * equal to len. Let k be the number of bytes actually read; these
     * bytes will be stored in elements b[off] through b[off+k-1],
     * leaving elements b[off+k] through b[off+len-1] unaffected.
     * <p>
     * In every case, elements b[0] through b[off] and elements
     * b[off+len] through b[b.length-1] are unaffected.
     * <p>
     * If the first byte cannot be read for any reason other than end
     * of file, then an IOException is thrown. In particular, an
     * IOException is thrown if the input stream has been closed.
     *
     * @param b the buffer into which the data is read.
     * @param off the start offset in array b at which the data is
     *            written.
     * @param len the maximum number of bytes to 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 IOException
     * @exception NullPointerException
     * @exception IndexOutOfBoundsException
     */

    public int read(final byte [] b, final int off, final int len)
        throws IOException, NullPointerException, IndexOutOfBoundsException
    {
        dieIfClosed();
        if (b == null)
        {
            throw new NullPointerException("buffer is null");
        }
        if ((off < 0) || (len < 0) || (b.length < (off + len)))
        {
            throw new IndexOutOfBoundsException(
                "can't read past buffer boundaries");
        }
        if (len == 0)
        {
            return 0;
        }
        if (atEOD())
        {
            return EOD;
        }
        int limit = Math.min(available(), len);

        if ((off == 0) && (limit == b.length))
        {
            _document.read(b, _current_offset);
        }
        else
        {
            byte[] buffer = new byte[ limit ];

            _document.read(buffer, _current_offset);
            System.arraycopy(buffer, 0, b, off, limit);
        }
        _current_offset += limit;
        return limit;
    }

    /**
     * Repositions this stream to the position at the time the mark
     * method was last called on this input stream.
     * <p>
     * The general contract of reset is:
     * <p>
     * <ul>
     *    <li>
     *        If the method markSupported returns true, then:
     *        <ul>
     *            <li>
     *                If the method mark has not been called since the
     *                stream was created, or the number of bytes read
     *                from the stream since mark was last called is
     *                larger than the argument to mark at that last
     *                call, then an IOException might be thrown.
     *            </li>
     *            <li>
     *                If such an IOException is not thrown, then the
     *                stream is reset to a state such that all the
     *                bytes read since the most recent call to mark
     *                (or since the start of the file, if mark has not
     *                been called) will be resupplied to subsequent
     *                callers of the read method, followed by any
     *                bytes that otherwise would have been the next
     *                input data as of the time of the call to reset.
     *             </li>
     *         </ul>
     *     </li>
     *     <li>
     *         If the method markSupported returns false, then:
     *         <ul>
     *             <li>
     *                 The call to reset may throw an IOException.
     *             </li>
     *             <li>
     *                 If an IOException is not thrown, then the
     *                 stream is reset to a fixed state that depends
     *                 on the particular type of the input and how it
     *                 was created. The bytes that will be supplied to
     *                 subsequent callers of the read method depend on
     *                 the particular type of the input stream.
     *             </li>
     *         </ul>
     *     </li>
     * </ul>
     * <p>
     * All well and good ... this class's markSupported method returns
     * true and this method does not care whether you've called mark
     * at all, or whether you've exceeded the number of bytes
     * specified in the last call to mark. We're basically walking a
     * byte array ... mark and reset to your heart's content.
     */

    public void reset()
    {
        _current_offset = _marked_offset;
    }

    /**
     * Skips over and discards n bytes of data from this input
     * stream. The skip method may, for a variety of reasons, end up
     * skipping over some smaller number of bytes, possibly 0. This
     * may result from any of a number of conditions; reaching end of
     * file before n bytes have been skipped is only one
     * possibility. The actual number of bytes skipped is returned. If
     * n is negative, no bytes are skipped.
     *
     * @param n the number of bytes to be skipped.
     *
     * @return the actual number of bytes skipped.
     *
     * @exception IOException
     */

    public long skip(final long n)
        throws IOException
    {
        dieIfClosed();
        if (n < 0)
        {
            return 0;
        }
        int new_offset = _current_offset + ( int ) n;

        if (new_offset < _current_offset)
        {

            // wrap around in converting a VERY large long to an int
            new_offset = _document_size;
        }
        else if (new_offset > _document_size)
        {
            new_offset = _document_size;
        }
        long rval = new_offset - _current_offset;

        _current_offset = new_offset;
        return rval;
    }

    private void dieIfClosed()
        throws IOException
    {
        if (_closed)
        {
            throw new IOException(
                "cannot perform requested operation on a closed stream");
        }
    }

    private boolean atEOD()
    {
        return _current_offset == _document_size;
    }
}   // end public class DocumentInputStream