Java: using regex to parse dxf file

Question

I'm beginning to write my own dxf file parser and I've ran across a regex problem. Consider the following text file (which is a snippet of a particular dxf file I'm working on):

http://www.filedropper.com/test_104

I read this file in as a String with:

String s = FileUtils.readFileToString(file);

I then want to use regex to split this string so I get an array of Strings of size two with the LINE entity as the first element and the MTEXT entity as the second. My first thought was to use:

String[] tokens = s.split("\\s{2,2}0");

The problem with this however (which you can test for yourself), is that it returns:

{"", "\nLINE...", "\nMTEXT...", "\n100...", "\n"}

Of course the first and last strings could easily be removed from the array, but if you look at the text file, you'll see that in the MTEXT entity there is

"    0"

i.e, four whitespaces and a 0. I don't want to split on this unfortunately. So my question is: how can I parse this using split and regex to simply obtain the array:

String[] tokens = {"\nLINE...", "\nMTEXT..."}

RokL · Accepted Answer · 2014-05-15 12:59:40Z

1

You can use positive look-ahead.

s.split("\\s\\s0(?=\\nLINE|\\nMTEXT)");

answered May 15, 2014 at 12:59

RokL

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3 Comments

CB_Maverick Over a year ago

Your absolutely correct. I had just noticed to that you could do: s.split("\\n\\s\\s0\\n") because of the way the end line characters are setup in the file.

CB_Maverick Over a year ago

Another question. Is there a way to compactify your above regex expression when testing all dxf entity objects. This list can be found here: link

RokL Over a year ago

Well if you found a good delimited like "\\n\\s\\s0\\n" then I recommend you use that. Generally I don't use split since sometimes it can be nearly impossible to construct an expression that precisely splits. I tend to use Pattern and Matcher object directly and examine matches for additional conditions (such as match starting one of particular keywords). I manually glue together matches that don't statify the condition to get the correct List of string fragments.

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