How to extract elements from a document

Question

I'm new to Java and I'm using JDOM in a JSP page. I've a document like this:
<OFFERTA>
<FACOLTA idFacolta="F1">
<CORSO value="xxx"/>
<CORSO value="yyy"/>
</FACOLTA>
<FACOLTA idFacolta="F2">
<CORSO value="zzz"/>
</FACOLTA>
<FACOLTA idFacolta="F3">
</FACOLTA>
<FACOLTA idFacolta="F4">
</FACOLTA>
</OFFERTA>
I'd like to get a document with the same structure but with the only FACOLTA elements that match a requested value for the idFacolta attribute.
For example, if the requested idFacolta is "F2", I'd like to get:
<OFFERTA>
<FACOLTA idFacolta="F2">
<CORSO value="zzz"/>
</FACOLTA>
</OFFERTA>
I check in a loop if the element matches the idFacolta requested but when I find and try to delete it I get:
java.util.ConcurrentModificationException
     at org.jdom.ContentList$FilterListIterator.checkConcurrentModification(ContentList.java:1230)
     at org.jdom.ContentList$FilterListIterator.hasNext(ContentList.java:942)
Here's my code:
Document doc = builder.build(file);
Element root = doc.getRootElement();
List children = root.getChildren();
Iterator facoltaIterator = children.iterator();
// Check if there's a request
if (id!=null) {
     while (facoltaIterator.hasNext()) {
          Element facolta = (Element) facoltaIterator.next();
          if (!facolta.getAttribute("idFacolta").getValue().equalsIgnoreCase(id)) {
               // Delete
               root.removeContent(facolta);
All seems to be right, except the line
root.removeContent(facolta);
So, I tried to make a new document for the results, adding the element facolta:
Document doc = builder.build(file);
Element root = doc.getRootElement();
// Create a new document with the same root
Element rootRisultati = new Element("OFFERTA");
Document docRisultati = new Document(rootRisultati);
List children = root.getChildren();
Iterator facoltaIterator = children.iterator();
if (id!=null) {
     while (facoltaIterator.hasNext()) {
          Element facolta = (Element) facoltaIterator.next();
          if (facolta.getAttribute("idFacolta").getValue().equalsIgnoreCase(id)) {
               // Add the element to the new document
               rootRisultati.addContent(facolta);
but this causes a different exception:
org.jdom.IllegalAddException: The element already has an existing parent "OFFERTA"
     at org.jdom.ContentList.add(ContentList.java:190)
     at org.jdom.ContentList.add(ContentList.java:146)
     at java.util.AbstractList.add(AbstractList.java:84)
     at org.jdom.Element.addContent(Element.java:1062)
I'm not able to find a solution.
There's a commonly used procedure to select elements maintaing the structure of the document?
Can anyone help please? Thanks in advance.
Stefano

Answer 1

maybe you could try posting this in a JDOM forum? JDOM is not a standard XML tool from Sun / for Java... therefore out of the scope of this forum!