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Java Forum / General / July 2007regex: find semicolon that is not part of an entity
Okay, I have something that works, but I don't like it: String SEMICOLON_NOT_ENTITY_REGEX = "(?<!&#?\\w{1,20}+);"; The part of the regex that says, "at least 1 but not more than 20" is a horrible addition that is the only way I could find around the odd Exception: java.util.regex.PatternSyntaxException: Look-behind group does not have an obvious maximum length near index 9 (?<!&#?\w+); ^ Is there any way around this? On Jul 16, 9:44 am, Robert Watkins <rwatkinsNOS...@NOSPAMfoo-bar.org> wrote: > Okay, I have something that works, but I don't like it: > [quoted text clipped - 10 lines] > > Is there any way around this? Does this regex work for you: "(&#?[^;]*;[^&]*)?;" Alternatively, you can use an XML parser, and wherever you find a ; in character data, you found a ; not part of an entity :-) > Does this regex work for you: "(&#?[^;]*;[^&]*)?;" Nope -- that one also finds semicolons that /are/ part of entities. > Alternatively, you can use an XML parser, and wherever you find a ; in > character data, you found a ; not part of an entity :-) Hmmm. I suppose, but that way more heavy-handed than I was hoping for (and probably far less performant than the regex I've got that works). All I'm doing is splitting a String on semicolons, while keeping entities intact. Thanks, -- Robert On Mon, 16 Jul 2007 16:44:17 GMT, Robert Watkins <rwatkinsNOSPAM@NOSPAMfoo-bar.org> wrote, quoted or indirectly quoted someone who said : >String SEMICOLON_NOT_ENTITY_REGEX I have written some classes for interconverting entities and chars. They use manual parsers. see http://mindprod.com/products.html#ENTITIES They also include big tables of known entities.  SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com > On Mon, 16 Jul 2007 16:44:17 GMT, Robert Watkins > <rwatkinsNOSPAM@NOSPAMfoo-bar.org> wrote, quoted or indirectly quoted [quoted text clipped - 6 lines] > http://mindprod.com/products.html#ENTITIES > They also include big tables of known entities. Thanks, but I don't want to convert the entities. All I'm doing is splitting a String on semicolons, while keeping entities intact. Thanks, -- Robert > All I'm doing is > splitting a String on semicolons, while keeping entities intact. It might be easier to solve the inverse problem, then: Find the strings that are separated by semi colons that are not part of an entity. I think the regular expression would look something like: ([^&;]|&[^&;]*;)*(&[^&;]*)? Where the last bit "(&[^&;]*)?" is only necessary if you want to allow for malformed XML where you have an unterminated entity (e.g. "<BadXML>Hello World &unterminated</BadXML>" What the regexp basically says is: <pseudoRegExp> ( Any character except '&' and ';' OR an entity; that is, '&' followed by any character except '&' and ';' followed by ';' ) zero or more times optionally followed by an unterminated entity. </pseudoRegExp> - Oliver >> All I'm doing is >> splitting a String on semicolons, while keeping entities intact. [quoted text clipped - 4 lines] > > ([^&;]|&[^&;]*;)*(&[^&;]*)? Thanks for this approach. It does work. Given that I will not allow malformaed entities, I've changed the regex to: ([^&;]|&#?\\w+;)* which also restricts the entity-specific regex a bit. It took me a while to respond because (along with all my other work!) I did a fair bit of testing with your approach, my original approach and with yet another approach: splitting on all semicolons, then reconstructing the strings that were split at the end of entities. What surprised me was that there weren't any hugely significant differences in the performance of all three approaches. I expected the string reconstruction to be way slower than the others, but the greatest difference in timing was a mere 8% (which could certainly be considered more significant in different contexts). I'm a bit reticent to admit that I started out as a Perl programmer -- and as such have always fancied myself fairly good with regular expressions -- but you've got me stumped here. While I was able to parse your original regex easily enough not to need your kindly provided pseudoRegExp, I have to admit that I can't figure out why the first character class needs to be [^&;]. Why does the & have to figure in; why could it not simply be: <pseudoRegExp> ( any character not a semicolon OR any entity ) zero or more times </pseudoRegExp> I tried this and it simply doesn't work, but I can't think why. Don't it always happen that way? I answered my own question moments after posting this repsonse to you. It's a matter of order. The regex you provided, and which I modified, tries to match the sole semicolons first, but without the & in the character class it finds the semicolons in entities before the regex has tried to match entities. Just switching things around a bit: (&#?\\w+;|[^;])* Gives the expected results and is (for me) much clearer, being essentially what I was looking for in my question to you: <pseudoRegExp> ( any entity OR any character not a semicolon ) zero or more times </pseudoRegExp> In any case, thank you again, you certainly pointed me in the right direction, having me look at the problem the other way 'round. -- Robert >>> All I'm doing is >>> splitting a String on semicolons, while keeping entities intact. [quoted text clipped - 38 lines] > > I tried this and it simply doesn't work, but I can't think why. On Tue, 17 Jul 2007 12:42:03 GMT, Robert Watkins <rwatkinsNOSPAM@NOSPAMfoo-bar.org> wrote, quoted or indirectly quoted someone who said : >Thanks, but I don't want to convert the entities. All I'm doing is >splitting a String on semicolons, while keeping entities intact. One way to skin that cat would be to convent the entities back to chars, then split on semicolons, then put the entities back. Consider there are also decimal and hex entities. You could use your code to find entities, or use mine. SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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