Re: How to convert CSV row to Java object?
On Fri, 3 Sep 2010, Arved Sandstrom wrote:
Lew wrote:
You should look at the information about CSV files on mindprod.com. One
think Roedy makes clear is that CSV is not simple or precise or
straightforward.
Well, "pure" or simple CSV - where only commas have any special meaning
in a line - is simple. As soon as you start adding any extra rules,
including anything at all to do with quotes or backslashes, then it
stops being simple;
I'd say that a format with these rules:
1. Rows are terminated by newlines
2. Within a row, values are separated by commas
3. A backslash followed by some character means that character as part of
a value, not as a syntactic element
3a. A backslash followed by end of file means end of file
Was still very simple. Code to read it looks like:
Reader in;
List<List<String>> rows = new ArrayList<List<String>>();
List<String> row = new ArrayList<String>();
StringBuilder buf = new StringBuilder();
int ch;
while ((ch = in.read()) != -1) {
if (ch == '\n') {
row.add(buf.toString());
buf.setLength(0);
rows.add(row);
row = new ArrayList<String>();
}
else if (ch == ',') {
row.add(buf.toString());
buf.setLength(0);
}
else if (ch == '\\') {
if ((ch = in.read()) != -1) {
buf.append((char)ch);
}
}
else {
buf.append((char)ch);
}
}
// if your last line is not properly terminated, you will have a nonempty
// row here; you might like to add that to rows, or you might not
My first cut at that also included a few lines to skip empty rows, and so
make last-line handling robust for free. It's so tempting to add bells and
whistles to something this simple.
The trouble is that the originators of CSV didn't choose backslash
escaping, they chose quoting, and doomed future generations to a world of
pain. ESR talks about this:
http://www.faqs.org/docs/artu/ch05s02.html
implementations that obey one set of rules or the other also stop being
compatible.
That's perhaps the major problem.
The thing is, when discussing delimiter-separated fields, commas are
often a poor choice for many sets of data, and a lot of these varying
and somewhat complicated rules exist precisely because commas are used.
Much better just to select a sensible delimiter.
True. I've always liked tabs, but they aren't very editor-friendly. A
system i talk to at work uses pipes. Some of the obscure ASCII controls
like RS could be good choices as long as you know the path the data is
travelling across is properly 7-bit clean.
tom
--
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being PERMANENTLY INVISIBLE.