Seek in huge xml-files

[Bogomir Engel]

Hi all,

For a student project I have to be able to look up information in
xml-files that are several GB big. Depending on the input of the user
through the GUI data has to be displayed. And it's not applicable to
parse the whole file for every input. We can't use DOM since it would
load the whole file into memory. Our current approaches are based on the
use of SAX. We thought of generating some sort of index for every data
set that would provide us the byte offset in the file. The Project has
to be implemented in Java, so we wanted to do something like

Reader.skip(offsetBytes)

So we could jump to the location where our data set is without having to
parse the whole file. The Problem with that is, that we don't have any
idea on how to obtain the index information. How can you find out, where
in a file the SAX parser is (meaning the byte offset)?

Another point is that our tests with the SAX parser when skipping bytes
in it's input source produced this exception.

Content is not allowed in prolog

So we are wondering, whether it's possible to jump to some given
position and then parse from there.

I'm thankful for any advice since I'm quite helpless now. Many Thanks!
Bogomir Engel

[jimmy Zhang]

if it is less than 2GB and you have enough memory, try vtd-xml
http://vtd-xml.sf.net

"Bogomir Engel" <bo*****@grafidelity.dewrote in message
news:g7*************@news.t-online.com...

Hi all,

For a student project I have to be able to look up information in
xml-files that are several GB big. Depending on the input of the user
through the GUI data has to be displayed. And it's not applicable to parse
the whole file for every input. We can't use DOM since it would load the
whole file into memory. Our current approaches are based on the use of
SAX. We thought of generating some sort of index for every data set that
would provide us the byte offset in the file. The Project has to be
implemented in Java, so we wanted to do something like

Reader.skip(offsetBytes)

So we could jump to the location where our data set is without having to
parse the whole file. The Problem with that is, that we don't have any
idea on how to obtain the index information. How can you find out, where
in a file the SAX parser is (meaning the byte offset)?

Another point is that our tests with the SAX parser when skipping bytes in
it's input source produced this exception.

Content is not allowed in prolog

So we are wondering, whether it's possible to jump to some given position
and then parse from there.

I'm thankful for any advice since I'm quite helpless now. Many Thanks!
Bogomir Engel

[Bogomir Engel]

We successfully completed the application.

javax.xml.stream.Location offers a method getCharacterOffset() which
does exactly what we needed.

This article was quite helpful:
Parsing XML documents partially with StAX
http://www.ibm.com/developerworks/xm...tx2/index.html

StAX is a very useful tool, when you don't have the memory to do it with
DOM and SAX offers insufficient control. For example one can decide how
to proceed in the parsing process at any time.

By the way, with some mapping JiBX (http://jibx.sourceforge.net/ very
recommendable) created ordinary Java objects out of the xml-data sets
for us. We saved the byte offsets in the objects during the initial
parsing process.