package org.apache.xpath.operations;
import javax.xml.transform.TransformerException;
import org.apache.xml.dtm.DTM;
import org.apache.xml.dtm.DTMIterator;
import org.apache.xml.dtm.DTMManager;
import org.apache.xpath.Expression;
import org.apache.xpath.XPathContext;
import org.apache.xpath.objects.XNodeSet;
import org.apache.xpath.objects.XObject;
/**
* This is a "smart" variable reference that is used in situations where
* an absolute path is optimized into a variable reference, but may
* be used in some situations where the document context may have changed.
* For instance, in select="document(doc/@href)//name[//salary > 7250]", the
* root in the predicate will be different for each node in the set. While
* this is easy to detect statically in this case, in other cases static
* detection would be very hard or impossible. So, this class does a dynamic check
* to make sure the document context of the referenced variable is the same as
* the current document context, and, if it is not, execute the referenced variable's
* expression with the current context instead.
*/
public class VariableSafeAbsRef extends Variable
{
/**
* Dereference the variable, and return the reference value. Note that lazy
* evaluation will occur. If a variable within scope is not found, a warning
* will be sent to the error listener, and an empty nodeset will be returned.
*
*
* @param xctxt The runtime execution context.
*
* @return The evaluated variable, or an empty nodeset if not found.
*
* @throws javax.xml.transform.TransformerException
*/
public XObject execute(XPathContext xctxt, boolean destructiveOK)
throws javax.xml.transform.TransformerException
{
XNodeSet xns = (XNodeSet)super.execute(xctxt, destructiveOK);
DTMManager dtmMgr = xctxt.getDTMManager();
int context = xctxt.getContextNode();
if(dtmMgr.getDTM(xns.getRoot()).getDocument() !=
dtmMgr.getDTM(context).getDocument())
{
Expression expr = (Expression)xns.getContainedIter();
xns = (XNodeSet)expr.asIterator(xctxt, context);
}
return xns;
}
}