Algorithms for string processing

Question

I have a question which make me think about how to improve speed and memory of system. I will describe it by example, I have this file which have some string:

<e>Customer</e>
    <a1>Customer Id</a1>
    <a2>Customer Name</a2>
<e>Person</e>

It similar to xml file.

Now, my solution is when I read <e>Customer</e>, I will read from that to a nearest tag and then, substring from <e>Customer</e> to a nearest tag.

It make the system need to process so much. I used only regular expression to do it. I thought I will do the same as real compiler which have some phases (lexical analysis, parser).

Any ideas?

Thanks in advance!

Why not define an actual XML document (you can define your own tags, so I think what you've shown may be already valid...), then just run it though one of the XML parsing libraries? — Clockwork-Muse, Apr 05 '13 at 16:07
Thanks for quick reply, it's just a challenge for me. I'm searching for open source xml to view, but all of open source use source from jdk. — Trung Huynh, Apr 05 '13 at 16:29
Although technically the JDK itself seems to be for Linux (deployment), a fair bit of the Java code itself should still be 'portable' - check out [OpenJDK](http://openjdk.java.net/) which is an open-source version of the JDK. — Clockwork-Muse, Apr 05 '13 at 17:29

score 2 · Answer 1 · answered Apr 05 '13 at 16:08

2

Regular expressions are not the right tool for parsing complex structures like this. Since your file looks a lot like XML, it may make sense to add what's missing to make it XML (i.e. the header), and feed the result to an XML parser.

XML parsers are optimized for processing large volumes of data quickly (especially the SAX kind). You should see a significant improvement in performance if you switch to parsing XML from processing large volumes of text with regular expressions.

answered Apr 05 '13 at 16:08

Sergey Kalinichenko

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I process data in PhoneGap and I think, in Javascript don't have a best xml parser. it's reason I do it. – Trung Huynh Apr 05 '13 at 16:34
@TrungHuynh For modestly large inputs, even the bad XML parsers would still beat a regex. – Sergey Kalinichenko Apr 05 '13 at 16:47
OK, I agree, so why don't I build a new parser which better for my purpose? – Trung Huynh Apr 05 '13 at 17:21
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Because adjusting your purpose slightly will save you several weeks of difficult and error-prone work, and give you a solution which works now. – user207421 Apr 06 '13 at 01:50

score 2 · Accepted Answer · edited May 23 '17 at 12:21

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If you really don't want to use one of the free and reliable xml parsers then a truly fast solution will almost certainly involve a state machine.

See this How to create a simple state machine in java question for a good start.

Please be sure to have a very good reason for taking this route.

edited May 23 '17 at 12:21

Community

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answered Apr 05 '13 at 16:12

OldCurmudgeon

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@TrungHuynh - I am sorry to hear that - good luck. There is plenty of resources covering state machines. – OldCurmudgeon Apr 05 '13 at 23:01

score 1 · Answer 3 · answered Apr 05 '13 at 16:07

1

Just don't invest the time into an XML lexer/parser (its not worth it) and use what is allready out there.

For example http://www.mkyong.com/tutorials/java-xml-tutorials/ is a good tutorial,just use google.

answered Apr 05 '13 at 16:07

Quonux

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Thanks, if have any language don't have XML lexer and parser built-in? – Trung Huynh Apr 05 '13 at 16:30

Algorithms for string processing

3 Answers3