FilteredInputStream is the right thing to extend.
Thank you again, Noel, for calling my attention to FilterInputStream. I had not previously understood what purpose FilterInputStream serves in the API. But your suggestion, coming after this programming exercise in which I've had to understand the consequences of calling read(byte[]) when my class does not override that method, has helped me understand a need for FilterInputStream.
> ... SMTPInputStream
implements read() based upon the real stream, which is the one non-constructor method that is correct in the code. The rest are wrong. For example:
public void close() throws IOException{ super.close(); }
explicitly illustrates a problem that is implicit with all of the inherited methods. The code invokes the inherited implementation, often a NO-OP. It ought to be delegating to the real stream.
In the particular case with SMTPDataInputStream, the class which I submit for your consideration, the underlying stream (the "real stream" as I understand your usage) is the BufferedInputStream which will later be read again by the envelope-command-line Reader. So, unless I am mistaken, we do not want to be closing the underlying stream in this case.
> ... FilteredInputStream provides the
core wrapper for delegation, allowing you to override just those methods that implement your unique behavior.
As I describe in the comment at the end of class SMTPDataInputStream, this implementation relies upon the behavior of the two InputStream methods read(byte[]) and read(byte[], int, int) which work by making repeated calls to the read() method in this descendant SMTPDataInputStream. In this case that behavior is needed, in order to use the functionality which I have added only in the read() method.
The read(byte[]) and read(byte[], int, int) methods of BufferedInputStream, which evidently would be employed if I extended FilterInputStream, do not behave this way, according to my tests. They appear to read directly from somewhere deeper, and thus would not express the functionality added in the one read() method.
But FilterInputStream does look like a class I will want to use another time, in a similar task.
Rich
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