Your question strongly suggests that you don't understand
how to use JTextArea and that you don't understand
much about the design of Swing. The read() method
is to be used only for initializing the component,
and not for keeping it up to date. All Swing components
keep their state in a data model - in the case of JTextArea
this is an implementation of Document. Modifying
the underlying data model is done through methods belonging
to the model.

The suggestion to use a piped stream is a bad one in this
context, although it will work just fine in general when piping
an output stream to an input stream.

I think you need to do some serious reading about Swing,
in particular about the Model/View/Controller pattern that
Swing uses. See the Swing FAQ for suggested references.

Used PipedInputStream and PipedOutputStream (or PipedReader and PipedWriter). You can find an explanation of how to do this at http://java.sun.com/docs/books/tutorial/essential/io/pipedstreams.htm.