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Posted to j-users@xerces.apache.org by Michal Sankot <sa...@seznam.cz> on 2004/01/16 16:48:49 UTC
problem with SAX - repetitive lines returned by characters()
Hi,
I have problem with SAX bit of Xerces. I use SAX to get lines of an element
of specified tag and print them out.
I was using older version of Xerces with which it run fine. When I replaced
old xerces.jar with new xercesImpl.jar SAX starts to behave wierd.
CDATA element content which is "1\n2\n3\n4\n" is returned by characters()
method as
"1\n"
"1\n"
"2\n"
"1\n"
"2\n"
"3\n"
"1\n"
"2\n"
"3\n"
"4\n"
strange (and frustrating), isn't it ?
what can be done with it ?
Michal
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Re: problem with SAX - repetitive lines returned by characters()
Posted by Michal Sankot <sa...@seznam.cz>.
ok,
I tried to isolate problematic part of code and found the culprit. I was
using two different buffers for saving incomming data, where the forst one
was saving data returned by characters and second appended sone other text
to the contents of first one, after parsing finished. Problem was that I
appended content of first buff to the second every(!) time characters were
called. Thus when there was more of contents, it was called more times and
caused repetition described in previous mails. It
Thanks,
Michal
> That's not impossible, but it seems unlikely unless you're perhaps
> using a very old version of Xerces. It seems a lot more likely
> there's a bug in your code. If you can provide a complete test case
> that demonstrates the alleged bug (the simpler the better) then I'd
> be more inclined to believe the bug is in Xerces, and perhaps someone
> could offer a fix.
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Re: problem with SAX - repetitive lines returned by characters()
Posted by Elliotte Rusty Harold <el...@metalab.unc.edu>.
At 10:51 AM +0000 1/19/04, Michal Sankot wrote:
>Hi,
>I agree with the points you mentioned, but the problem is exactly that
>Xerces doesn't behave the way you say (and which I expected to encounter).
That's not impossible, but it seems unlikely unless you're perhaps
using a very old version of Xerces. It seems a lot more likely
there's a bug in your code. If you can provide a complete test case
that demonstrates the alleged bug (the simpler the better) then I'd
be more inclined to believe the bug is in Xerces, and perhaps someone
could offer a fix.
--
Elliotte Rusty Harold
elharo@metalab.unc.edu
Effective XML (Addison-Wesley, 2003)
http://www.cafeconleche.org/books/effectivexml
http://www.amazon.com/exec/obidos/ISBN%3D0321150406/ref%3Dnosim/cafeaulaitA
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Re: problem with SAX - repetitive lines returned by characters()
Posted by Michal Sankot <sa...@seznam.cz>.
Hi,
I agree with the points you mentioned, but the problem is exactly that
Xerces doesn't behave the way you say (and which I expected to encounter).
characters() method I use is standart SAX characters method (same as you use
in your Fibonacci example)
-------
public void characters(char[] text, int start, int length) {
if (processing) {
buffer.append(text,start,length);
}
}
public void startElement(...) {
if (localName.equals(codeName)) {
buffer = new StringBuffer();
processing=true;
}
}
public void endElement(...) {
if (localName.equals(codeName)) {
processing=false;
System.out.println(buffer.toString())
buffer.setLength(0);
}
}
-------
It's code I'd expect to work. Problem is that
- every char array returned by characters() has start=0 and length covering
full length of returned text. (so it doesn't return any data which aren't
meant to be not accepted)
- it returns what was returned before, with all chars of array marked as
valid (to be accepted)
so what I get for "1\n2\n3\n4\n" is (where real lines are longer, not just
one digit)
"1\n" : start =0, length =2
"1\n" : start =0, length =2
"2\n" : start =0, length =2
"1\n" : start =0, length =2
"2\n" : start =0, length =2
"3\n" : start =0, length =2
"1\n" : start =0, length =2
"2\n" : start =0, length =2
"3\n" : start =0, length =2
"4\n" : start =0, length =2
To me it seems that there may be problem with version mismatch of
InputSourcem or other classes which pass document to SAX itslef.
Michal
> At 3:48 PM +0000 1/16/04, Michal Sankot wrote:
> >I have problem with SAX bit of Xerces. I use SAX to get lines of an
element
> >of specified tag and print them out.
> >I was using older version of Xerces with which it run fine. When I
replaced
> >old xerces.jar with new xercesImpl.jar SAX starts to behave wierd.
> >
> >CDATA element content which is "1\n2\n3\n4\n" is returned by characters()
> >method as
> >"1\n"
> >"1\n"
> >"2\n"
> >
> >"1\n"
> >
> >"2\n"
> >"3\n"
> >"1\n"
> >"2\n"
> >"3\n"
> >"4\n"
> >strange (and frustrating), isn't it ?
> >
>
> I don't think so. Remember SAX parsers are not required to report all
> character data in a single call to characters. They can and do split
> nodes across multiple calls. You need to buffer and accumulate the
> data until you're ready to use it.
>
> You also have one or both of two other problems. The char array
> passed to characters() is not minimal. It normally contains other
> data not related to the current invocation. You need to use the start
> and length arguments to extract the sub-array relevant to the current
> call.
>
> Finally, the array passed to characters may be reused by the parser.
> You should not store it. Any data you need should be copied into some
> other object. See
>
> http://www.cafeconleche.org/books/xmljava/chapters/ch06s07.html
>
> for more discussion of these points.
> --
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Re: problem with SAX - repetitive lines returned by characters()
Posted by Elliotte Rusty Harold <el...@metalab.unc.edu>.
At 3:48 PM +0000 1/16/04, Michal Sankot wrote:
>Hi,
>I have problem with SAX bit of Xerces. I use SAX to get lines of an element
>of specified tag and print them out.
>I was using older version of Xerces with which it run fine. When I replaced
>old xerces.jar with new xercesImpl.jar SAX starts to behave wierd.
>
>CDATA element content which is "1\n2\n3\n4\n" is returned by characters()
>method as
>"1\n"
>"1\n"
>"2\n"
>
>"1\n"
>
>"2\n"
>"3\n"
>"1\n"
>"2\n"
>"3\n"
>"4\n"
>strange (and frustrating), isn't it ?
>
I don't think so. Remember SAX parsers are not required to report all
character data in a single call to characters. They can and do split
nodes across multiple calls. You need to buffer and accumulate the
data until you're ready to use it.
You also have one or both of two other problems. The char array
passed to characters() is not minimal. It normally contains other
data not related to the current invocation. You need to use the start
and length arguments to extract the sub-array relevant to the current
call.
Finally, the array passed to characters may be reused by the parser.
You should not store it. Any data you need should be copied into some
other object. See
http://www.cafeconleche.org/books/xmljava/chapters/ch06s07.html
for more discussion of these points.
--
Elliotte Rusty Harold
elharo@metalab.unc.edu
Effective XML (Addison-Wesley, 2003)
http://www.cafeconleche.org/books/effectivexml
http://www.amazon.com/exec/obidos/ISBN%3D0321150406/ref%3Dnosim/cafeaulaitA
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