XML and ID node (dtd)

[Jean-Philippe Martin]

Hi all,

I parse a XML file to get a DOM Document.

But when I use the method Document.getElementsByID(String Id) each time I receive null.

My XML follow a DTD. But I don't know where to tell to my parser to use this DTD.

How can I tell it ? and does it change anything to the result of the above method ?

thx in advance, Jean-Philippe

 

[Martin Honnen]

I parse a XML file to get a DOM Document.

But when I use the method Document.getElementsByID(String Id) each time I receive null.

There is no method getElementsByID in the W3C DOM. There is method document.getElementById

My XML follow a DTD. But I don't know where to tell to my parser to use this DTD.

How can I tell it ? and does it change anything to the result of the above method ?

Which parser are you using? How do you use the parser, with a programming language, for instance Java?

 

[Jean-Philippe Martin]

you're right. )

I've use the tutorial example available on java.sun.com

Here a the begining of the source code to open and parse the file with Java.

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance;

try{
DocumentBuilder builder = factory.newDocumentBuilder;
Document doc = builder.parse(new File(FileName));
} catch(....)

After that point I'm able to use the "doc" variable.

Thanks in advance.

 

[Johannes Koch]

Jean-Philippe Martin wrote:

[Document.getElementsByID(String Id)]

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance;

try{
DocumentBuilder builder = factory.newDocumentBuilder;
Document doc = builder.parse(new File(FileName));
} catch(....)

After that point I'm able to use the "doc" variable.

I think, you have to enable validation to successfully use getElementByID.

 

[Martin Honnen]

Jean-Philippe Martin wrote:

I've use the tutorial example available on java.sun.com

Here a the begining of the source code to open and parse the file with Java.

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance;

try{
DocumentBuilder builder = factory.newDocumentBuilder;
Document doc = builder.parse(new File(FileName));
} catch(....)

After that point I'm able to use the "doc" variable.

With the following example Java program

import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.DocumentBuilder;
import org.w3c.dom.Document;
import org.w3c.dom.Element;

public class Test20040302 {
public static void main (String args) {
try {
DocumentBuilderFactory docBuilderFactory =
DocumentBuilderFactory.newInstance;
DocumentBuilder docBuilder = docBuilderFactory.newDocumentBuilder; Document xmlDocument = docBuilder.parse(args[0]); if (xmlDocument != null) { Element god = xmlDocument.getElementById("Kibo"); if (god != null) { System.out.println(god.getAttribute("home")); } else { System.out.println("Element not found."); } } } catch (Exception e) { System.out.println(e); } } }

when I pass in the filename of the following XML on the command line

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE gods [
<!ELEMENT gods (god)+>
<!ELEMENT god EMPTY>
<!ATTLIST god
name ID #REQUIRED
home CDATA #IMPLIED>
]>
<gods>
<god name="Kibo" home="http://www.kibo.com/" /> <god name="Xibo" /> </gods>

then getElementById("Kibo") finds the right element.

 

[Jean-Philippe Martin]

Thx I will try it at home.

 

[Jean-Philippe Martin]

Your example works fine, but have you tried to add an element with a method ?

for example this method:

static void addNode(Document doc) {
Element elem = doc.createElement("god");
elem.setAttribute("home", "AvProc");
elem.setAttribute("name", "Butch");
((Element)
doc.getElementsByTagName("gods").item(0)).appendChild(elem);

}

if you use it in your example, by instance after the search of "kibo"'s home, you won't be able to find "Butch"'s home with a getElementById("Butch").

In my application, I construct the xml file dynamically with this kind of method.

Thx, I hope you see the problem.

Best regards Jean-Philippe.

 

[Jean-Philippe Martin]

Here is a copy/paste of the Java api about this methods:

getElementById
public Element getElementById(java.lang.String elementId) Returns the Element whose ID is given by elementId. If no such element exists, returns null. Behavior is not defined if more than one element has this ID.
Note: The DOM implementation must have information that says which attributes are of type ID. Attributes with the name "ID" are not of type ID unless so defined. Implementations that do not know whether attributes are of type ID or not are expected to return null.

Parameters:
elementId - The unique id value for an element.
Returns:
The matching element.
Since:
DOM Level 2

How can I inform the DOM implementation ???

Thx for your help.

 

[Martin Honnen]

Your example works fine, but have you tried to add an element with a method ?

for example this method:

static void addNode(Document doc) {
Element elem = doc.createElement("god");
elem.setAttribute("home", "AvProc");
elem.setAttribute("name", "Butch");
((Element)
doc.getElementsByTagName("gods").item(0)).appendChild(elem);

}

if you use it in your example, by instance after the search of "kibo"'s home, you won't be able to find "Butch"'s home with a getElementById("Butch").

In my application, I construct the xml file dynamically with this kind of method.

That seems odd to me, but I can confirm that problem with Java 1.4.1_02. I consider that a bug, I think if the implementation reads in the DTD and getElementById finds elements parsed from a serialized XML document then it should also find elements created with the DOM. I googled around to find out if anyone else run into this but I haven't found anything about that. There are other Java DOM parsers than the one the Sun JRE comes with, maybe XercesJ from http://xml.apache.org/ doesn't have the problem.

 

[Jean-Philippe Martin]

It's not THE answer but it's an answer )

Thx for your time ! You're one of the few persons who try to help me.

I will try with another parser.I will post the result next time.

Have a nice day.

Jean-Philippe.

 

[Martin Honnen]

It's not THE answer but it's an answer )

Thx for your time ! You're one of the few persons who try to help me.

I will try with another parser.I will post the result next time.

It seems that the Java implementations somehow fail to have getElementById work on dynamically created and inserted elements:
http://lists.w3.org/Archives/Public/www-dom/2002JulSep/0005.html

DOM Level 3 introduces some new methods to specify an attribute is of type id but I still think if the DTD defines that then a DOM Level 2 implementation should do.