OpenTop Input/Output Facilities
OpenTop contains classes for managing both files and streams of
data.
Possibly the most admired feature of the Java™ and .NET™
input/output models is their explicit separation of byte and Unicode character streams and the flexible
way in which these streams can be filtered, extended and combined.
OpenTop offers an alternative to standard C++ streams,
providing a rich set of classes inspired by the Java API.
Of course OpenTop applications are not obliged to use the OpenTop I/O streams,
but their flexibility, power and ease of use often makes them an ideal
choice over the standard alternative.
Byte Streams
For applications that need to read/write bytes of data,
OpenTop provides the abstract
InputStream and
OutputStream
interfaces. These interfaces define the minimum set of operations
(such as read(), write(), close() and so on) which all byte streams implement.
OpenTop supplies concrete implementations of these interfaces for
writing to and reading from data files, the console, network sockets,
in-memory buffers and more. These classes perform a similar role to the standard C++
streambuf class but, because they are only concerned with the
specific task of reading or writing bytes and don't concern themselves
with ancillary tasks such as buffering or encoding, they are considerably
easier to understand and implement.
Filter Streams
So far we have only discussed streams which connect to a tangible
store of bytes. However, one of the most elegant features of OpenTop
streams is that they can be wrapped by other streams. This process is
called filtering and the streams which perform this task
are called filter streams.
A filter stream implements the InputStream or OutputStream
interface and also contains a reference to another InputStream or OutputStream
which is the filtered stream. The filter delegates read and write requests
to the contained stream, but performs some additional function such as
buffering the data to improve efficiency.
The BufferedInputStream
class is an example of a filter stream which aids performance by placing
a buffer between the reader and the data store. The elegance of this design
is demonstrated here because any input stream can now take advantage
of efficient buffering simply by being wrapped by
a BufferedInputStream, thereby removing the need for individual
streams to perform this task themselves.
By combining streams with one or more filters, the application is
able to create a virtual
pipeline through which data travels on its journey to or from
the data store. In some ways the OpenTop streams mirror the UNIX command filter
paradigm; where each filter stream performs one specific, identifiable task,
and multiple filters can be built-up into a pipeline to perform more complex tasks.
Unicode Character Streams (Readers and Writers)
In addition to the byte streams described above, OpenTop
contains streams for reading and writing Unicode characters. The Unicode
character stream equivalent to InputStream and OutputStream
are
Reader and
Writer respectively.
Unicode characters are often serialized to an external data source as
an encoded stream of bytes. OpenTop provides the
InputStreamReader and
OutputStreamWriter
classes which can decode or encode Unicode characters using any of the
wide range of
supplied Unicode encodings.
Just like their byte stream equivalents, Readers and Writers
support the filter paradigm as exemplified by the
BufferedReader class.
Additionally, streams are provided which buffer their characters in memory or
store them in string objects.
Platform-independent File System Access
Even though the C++ standard defines the fstream class for
performing file i/o, one of the perennial frustrations for cross-platform developers
is the lack of a standard facility to navigate the file system, e.g.
listing directories or determining a file's attributes.
OpenTop provides the File class
which gives application developers a portable method of accessing file
and directory information.
