Problem with Xerces-J

[Louis-Philippe Huberdeau]

The solution to this problem is probably very simple but I can't seem to
find any information about it. I'm trying to parse an XML document with
the Xerces-J (xml.apache.org) DOM implentation. I don't know how common
is the usage of that library but it seemed to be the most documented one
I could find.

The problem is that many functions return child elements as NodeList.
NodeList being a list of Node, I tryed to cast them as Element, to be
able to use getAttribute() on them. When I do so, I get a
ClassCastException. Is there a way to to convert a Node to an Element?

I also have a theorical question, which will probably solve the problem
above... What is the difference between a Node and an Element in XML? In
what cases is a Node not an Element? I'm just trying to figure out why
they seperated both. I'm sure there is a good reason, but I couldn't
find it explicitly and as a student, I don't have enough time to read
the entire specification to find this single information.

--
Louis-Philippe Huberdeau

[A. Bolmarcich]

In article <fJ*******************@news20.bellglobal.com>, Louis-Philippe Huberdeau wrote:

The solution to this problem is probably very simple but I can't seem to
find any information about it. I'm trying to parse an XML document with
the Xerces-J (xml.apache.org) DOM implentation. I don't know how common
is the usage of that library but it seemed to be the most documented one
I could find.

The problem is that many functions return child elements as NodeList.
NodeList being a list of Node, I tryed to cast them as Element, to be
able to use getAttribute() on them. When I do so, I get a
ClassCastException. Is there a way to to convert a Node to an Element?
A quick look at

http://xml.apache.org/xerces2-j/java.../NodeList.html

shows that NodeList has a Node item(int) method. Invoking item(0) on a
NodeList should return the first Node of the NodeList.
I also have a theorical question, which will probably solve the problem
above... What is the difference between a Node and an Element in XML? In
what cases is a Node not an Element? I'm just trying to figure out why
they seperated both. I'm sure there is a good reason, but I couldn't
find it explicitly and as a student, I don't have enough time to read
the entire specification to find this single information.

A quick look at

http://xml.apache.org/xerces2-j/java.../dom/Node.html

shows that the list of subinterfaces of Node Element and other
non-element types types, such as Attr and CharacterData.

[Louis-Philippe Huberdeau]

A. Bolmarcich wrote:

In article <fJ*******************@news20.bellglobal.com>, Louis-Philippe Huberdeau wrote:

The solution to this problem is probably very simple but I can't seem to
find any information about it. I'm trying to parse an XML document with
the Xerces-J (xml.apache.org) DOM implentation. I don't know how common
is the usage of that library but it seemed to be the most documented one
I could find.

The problem is that many functions return child elements as NodeList.
NodeList being a list of Node, I tryed to cast them as Element, to be
able to use getAttribute() on them. When I do so, I get a
ClassCastException. Is there a way to to convert a Node to an Element?

A quick look at

http://xml.apache.org/xerces2-j/java.../NodeList.html

shows that NodeList has a Node item(int) method. Invoking item(0) on a
NodeList should return the first Node of the NodeList.

That's not the problem, I can get the Node, I just can't use it as an
Element to use the methods I really want to use.

I also have a theorical question, which will probably solve the problem
above... What is the difference between a Node and an Element in XML? In
what cases is a Node not an Element? I'm just trying to figure out why
they seperated both. I'm sure there is a good reason, but I couldn't
find it explicitly and as a student, I don't have enough time to read
the entire specification to find this single information.

A quick look at

http://xml.apache.org/xerces2-j/java.../dom/Node.html

shows that the list of subinterfaces of Node Element and other
non-element types types, such as Attr and CharacterData.

I just tought about something related to that. I will test it out
tomorrow and give you feedback about it.

Thank you for your time.

--
Louis-Philippe Huberdeau

[Philippe Poulard]

Louis-Philippe Huberdeau wrote:

The solution to this problem is probably very simple but I can't seem to
find any information about it. I'm trying to parse an XML document with
the Xerces-J (xml.apache.org) DOM implentation. I don't know how common
is the usage of that library but it seemed to be the most documented one
I could find.

The problem is that many functions return child elements as NodeList.
NodeList being a list of Node, I tryed to cast them as Element, to be
able to use getAttribute() on them. When I do so, I get a
ClassCastException. Is there a way to to convert a Node to an Element?

I also have a theorical question, which will probably solve the problem
above... What is the difference between a Node and an Element in XML? In
what cases is a Node not an Element? I'm just trying to figure out why
they seperated both. I'm sure there is a good reason, but I couldn't
find it explicitly and as a student, I don't have enough time to read
the entire specification to find this single information.

--
Louis-Philippe Huberdeau

Hi,

In the data model, all object of the document (and it is true for the
Document itself) is a Node.
So, an Element is also a Node.
But a Node may be something else than an Element, for example, a Text
(there is a dozen of types).
So, when you've a NodeList, you should test wich kind of node you got
before casting it :

Node node = list.item(i);
if (node.getNodeType()==Node.ELEMENT_NODE) {
Element el = (Element) node;
// your stuff here
}

Notice that in the following document :
<foo>
<bar>
</foo>
the NodeList obtained from the foo Element will return 3 nodes :
-a text node with &#xA;
-an element node named bar
-a text node with &#xA;
--
Cordialement,

///
(. .)
-----ooO--(_)--Ooo-----
| Philippe Poulard |
-----------------------

[Louis-Philippe Huberdeau]

Thanks for the information, that did work. I just never tought a blank
space could be a node.

Philippe Poulard wrote:

Louis-Philippe Huberdeau wrote:

The solution to this problem is probably very simple but I can't seem
to find any information about it. I'm trying to parse an XML document
with the Xerces-J (xml.apache.org) DOM implentation. I don't know how
common is the usage of that library but it seemed to be the most
documented one I could find.

The problem is that many functions return child elements as NodeList.
NodeList being a list of Node, I tryed to cast them as Element, to be
able to use getAttribute() on them. When I do so, I get a
ClassCastException. Is there a way to to convert a Node to an Element?

I also have a theorical question, which will probably solve the
problem above... What is the difference between a Node and an Element
in XML? In what cases is a Node not an Element? I'm just trying to
figure out why they seperated both. I'm sure there is a good reason,
but I couldn't find it explicitly and as a student, I don't have
enough time to read the entire specification to find this single
information.

--
Louis-Philippe Huberdeau

Hi,

In the data model, all object of the document (and it is true for the
Document itself) is a Node.
So, an Element is also a Node.
But a Node may be something else than an Element, for example, a Text
(there is a dozen of types).
So, when you've a NodeList, you should test wich kind of node you got
before casting it :

Node node = list.item(i);
if (node.getNodeType()==Node.ELEMENT_NODE) {
Element el = (Element) node;
// your stuff here
}

Notice that in the following document :
<foo>
<bar>
</foo>
the NodeList obtained from the foo Element will return 3 nodes :
-a text node with &#xA;
-an element node named bar
-a text node with &#xA;