bufferedreader.java

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    *
    * @exception IOException If an error occurs.
    */
  public int read(char[] buf, int offset, int count) throws IOException
  {
    synchronized (lock)
      {
	checkStatus();
	// Once again, we need to handle the special case of a readLine
	// that has a '\r' at the end of the buffer.  In this case, we'll
	// need to skip a '\n' if it is the next char to be read.
	// This special case is indicated by 'pos > limit'.
	boolean retAtEndOfBuffer = false;

	int avail = limit - pos;
	if (count > avail)
	  {
	    if (avail > 0)
	      count = avail;
	    else // pos >= limit
	      {
		if (limit == buffer.length)
		  markPos = -1; // read too far - invalidate the mark.
		if (pos > limit)
		  {
		    // Set a boolean and make pos == limit to simplify things.
		    retAtEndOfBuffer = true;
		    --pos;
		  }
		if (markPos < 0)
		  {
		    // Optimization:  can read directly into buf.
		    if (count >= buffer.length && !retAtEndOfBuffer)
		      return in.read(buf, offset, count);
		    pos = limit = 0;
		  }
		avail = in.read(buffer, limit, buffer.length - limit);
		if (retAtEndOfBuffer && avail > 0 && buffer[limit] == '\n')
		  {
		    --avail;
		    limit++;
		  }
		if (avail < count)
		  {
		    if (avail <= 0)
		      return avail;
		    count = avail;
		  }
		limit += avail;
	      }
	  }
	System.arraycopy(buffer, pos, buf, offset, count);
	pos += count;
	return count;
      }
  }

  /* Read more data into the buffer.  Update pos and limit appropriately.
     Assumes pos==limit initially.  May invalidate the mark if read too much.
     Return number of chars read (never 0), or -1 on eof. */
  private int fill() throws IOException
  {
    checkStatus();
    // Handle the special case of a readLine that has a '\r' at the end of
    // the buffer.  In this case, we'll need to skip a '\n' if it is the
    // next char to be read.  This special case is indicated by 'pos > limit'.
    boolean retAtEndOfBuffer = false;
    if (pos > limit)
      {
        retAtEndOfBuffer = true;
	--pos;
      }

    if (markPos >= 0 && limit == buffer.length)
      markPos = -1;
    if (markPos < 0)
      pos = limit = 0;
    int count = in.read(buffer, limit, buffer.length - limit);
    if (count > 0)
      limit += count;

    if (retAtEndOfBuffer && buffer[pos] == '\n')
      {
	--count;
	// If the mark was set to the location of the \n, then we
	// must change it to fully pretend that the \n does not
	// exist.
	if (markPos == pos)
	  ++markPos;
	++pos;
      }

    return count;
  }
  
  public int read() throws IOException
  {
    synchronized (lock)
      {
	checkStatus();
	if (pos >= limit && fill () <= 0)
	  return -1;
	return buffer[pos++];
      }
  }

  /* Return the end of the line starting at this.pos and ending at limit.
   * The index returns is *before* any line terminators, or limit
   * if no line terminators were found.
   */
  private int lineEnd(int limit)
  {
    int i = pos;
    for (; i < limit; i++)
      {
	char ch = buffer[i];
	if (ch == '\n' || ch == '\r')
	  break;
      }
    return i;
  }

  /**
    * This method reads a single line of text from the input stream, returning
    * it as a <code>String</code>.  A line is terminated by "\n", a "\r", or
    * an "\r\n" sequence.  The system dependent line separator is not used.
    * The line termination characters are not returned in the resulting
    * <code>String</code>.
    * 
    * @return The line of text read, or <code>null</code> if end of stream.
    * 
    * @exception IOException If an error occurs
    */
  public String readLine() throws IOException
  {
    checkStatus();
    // Handle the special case where a previous readLine (with no intervening
    // reads/skips) had a '\r' at the end of the buffer.
    // In this case, we'll need to skip a '\n' if it's the next char to be read.
    // This special case is indicated by 'pos > limit'.
    if (pos > limit)
      {
	int ch = read();
	if (ch < 0)
	  return null;
	if (ch != '\n')
	  --pos;
      }
    int i = lineEnd(limit);
    if (i < limit)
      {
	String str = new String(buffer, pos, i - pos);
	pos = i + 1;
	// If the last char in the buffer is a '\r', we must remember
	// to check if the next char to be read after the buffer is refilled
	// is a '\n'.  If so, skip it.  To indicate this condition, we set pos
	// to be limit + 1, which normally is never possible.
	if (buffer[i] == '\r')
	  if (pos == limit || buffer[pos] == '\n')
	    pos++;
	return str;
      }
    StringBuffer sbuf = new StringBuffer(200);
    sbuf.append(buffer, pos, i - pos);
    pos = i;
    // We only want to return null when no characters were read before
    // EOF.  So we must keep track of this separately.  Otherwise we
    // would treat an empty `sbuf' as an EOF condition, which is wrong
    // when there is just a newline.
    boolean eof = false;
    for (;;)
      {
	int ch = read();
	if (ch < 0)
	  {
	    eof = true;
	    break;
	  }
	if (ch == '\n' || ch == '\r')
	  {
	    // Check here if a '\r' was the last char in the buffer; if so,
	    // mark it as in the comment above to indicate future reads
	    // should skip a newline that is the next char read after
	    // refilling the buffer.
	    if (ch == '\r')
	      if (pos == limit || buffer[pos] == '\n')
	        pos++;
	    break;
	  }
	i = lineEnd(limit);
	sbuf.append(buffer, pos - 1, i - (pos - 1));
	pos = i;
      }
    return (sbuf.length() == 0 && eof) ? null : sbuf.toString();
  }

  /**
    * This method skips the specified number of chars in the stream.  It
    * returns the actual number of chars skipped, which may be less than the
    * requested amount.
    * <p>
    * This method first discards chars in the buffer, then calls the
    * <code>skip</code> method on the underlying stream to skip the remaining chars.
    *
    * @param num_chars The requested number of chars to skip
    *
    * @return The actual number of chars skipped.
    *
    * @exception IOException If an error occurs
    */
  public long skip(long count) throws IOException
  {
    synchronized (lock)
      {
	checkStatus();
	if (count <= 0)
	  return 0;
	// Yet again, we need to handle the special case of a readLine
	// that has a '\r' at the end of the buffer.  In this case, we need
	// to ignore a '\n' if it is the next char to be read.
	// This special case is indicated by 'pos > limit' (i.e. avail < 0).
	// To simplify things, if we're dealing with the special case for
	// readLine, just read the next char (since the fill method will
	// skip the '\n' for us).  By doing this, we'll have to back up pos.
	// That's easier than trying to keep track of whether we've skipped
	// one element or not.
	int ch;
	if (pos > limit)
	  if ((ch = read()) < 0)
	    return 0;
	  else
	    --pos; 

	int avail = limit - pos;

	if (count < avail)
	  {
	    pos += count;
	    return count;
	  }

	pos = limit;
	long todo = count - avail;
	if (todo > buffer.length)
	  {
	    markPos = -1;
	    todo -= in.skip(todo);
	  }
	else
	  {
	    while (todo > 0)
	      {
		avail = fill();
		if (avail <= 0)
		  break;
		if (avail > todo)
		  avail = (int) todo;
		pos += avail;
		todo -= avail;
	      }
	  }
	return count - todo;
      }
  }
  
  private void checkStatus() throws IOException
  {
    if (in == null)
      throw new IOException("Stream closed");
  }  
}