[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: [OT] bugs in JDK regex engine ?
On 2008-02-03 23:26:58 -0500 "Mukul Gandhi" <gandhi.mukul@g...> wrote: > String str = "<root><abc x='1'>text1</abc><pqr > y='1'>text2</pqr></root>"; > > Pattern pattern = Pattern.compile("<[^/]+>"); //anything from '<' to > '>', and not having '/' > Matcher matcher = pattern.matcher(str); > > while (matcher.find()) { > String group = matcher.group(); > System.out.println(group); > } > > 'str' is a String representation of a XML fragment. > > I want to extract all pieces from the string (the tokens), which form > a start tag (including attribute parts). > > I am expecting output: > <root> > <abc x='1'> > <pqr y='1'> But that's not what you asked for. You said "longest string starting with '<' and ending with '>' that doesn't contain '/'. > But the output produced by the above program is: > <root><abc x='1'> > <pqr y='1'> Yup. Exactly matches the regex. No / in either one, is there? Specifically, even though you think you asked for "just the start tag," you have <abc> nested inside <root>; there's no / anywhere around to prevent the regex from matching to the end of <abc> The problem with using regular expressions to parse any grammar with paired tokens (XML for example, but also most programming languages with paired braces of any sort, or comments in a language that permits comment nesting) is that regular expressions can't handle parity. You need something more powerful than regex. If you're determined to find the next layer of problems associated with using a too-weak tool to do the job, you should find it shortly after making this change: Pattern.compile("<[^/<]+>"); That prevents it from picking up a nested element tag. Most of the time. For giggles: <root><?my-pi wotsit ?><abc x='1'><![CDATA[<?xml version="1.0?> <root><abc x='1'>text1]]></abc> </root> HTH. Amy! -- Amelia A. Lewis amyzing {at} talsever.com Confidence: a feeling peculiar to the stage just before full comprehension of the problem.
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