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////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2018-2022 Saxonica Limited
// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
// This Source Code Form is "Incompatible With Secondary Licenses", as defined by the Mozilla Public License, v. 2.0.
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
package net.sf.saxon.sxpath;
import net.sf.saxon.Controller;
import net.sf.saxon.expr.Expression;
import net.sf.saxon.expr.StaticContext;
import net.sf.saxon.expr.XPathContextMajor;
import net.sf.saxon.expr.instruct.Executable;
import net.sf.saxon.expr.instruct.SlotManager;
import net.sf.saxon.om.Item;
import net.sf.saxon.om.ItemConsumer;
import net.sf.saxon.om.SequenceIterator;
import net.sf.saxon.om.SequenceTool;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.type.ItemType;
import net.sf.saxon.type.TypeHierarchy;
import java.util.ArrayList;
import java.util.List;
/**
* This class is a representation of an XPath Expression for use with the {@link XPathEvaluator} class.
* It is modelled on the XPath API defined in JAXP 1.3, but is free-standing, and is more strongly typed.
* In Saxon 9.6, the methods that returned Object and did implicit conversion to a native Java object
* have been removed; all conversions must now be done explicitly.
*
*/
public class XPathExpression {
private final StaticContext env;
private final Expression expression;
private SlotManager stackFrameMap;
private final Executable executable;
private int numberOfExternalVariables;
/**
* The constructor is protected, to ensure that instances can only be
* created using the createExpression() or createPattern() method of XPathEvaluator
*
* @param env the static context of the expression
* @param exp the internal representation of the compiled expression
* @param exec the Executable associated with this expression
*/
protected XPathExpression(StaticContext env, Expression exp, Executable exec) {
expression = exp;
this.env = env;
this.executable = exec;
}
/**
* Get the Executable associated with this expression
* @return the associated Executable
*/
public Executable getExecutable() {
return executable;
}
/**
* Define the number of slots needed for local variables within the expression
*
* @param map the stack frame map identifying all the variables used by the expression, both
* those declared internally, and references to variables declared externally
* @param numberOfExternalVariables the number of slots in the stack frame allocated to
* externally-declared variables. These must be assigned a value before execution starts
*/
protected void setStackFrameMap(SlotManager map, int numberOfExternalVariables) {
stackFrameMap = map;
this.numberOfExternalVariables = numberOfExternalVariables;
}
/**
* Create a dynamic context suitable for evaluating this expression, without supplying a context
* item
*
* @return an XPathDynamicContext object representing a suitable dynamic context. This will
* be initialized with a stack frame suitable for holding the variables used by the
* expression.
*/
public XPathDynamicContext createDynamicContext() {
XPathContextMajor context = new XPathContextMajor(null, executable);
context.openStackFrame(stackFrameMap);
return new XPathDynamicContext(env.getRequiredContextItemType(), context, stackFrameMap);
}
/**
* Create a dynamic context suitable for evaluating this expression
*
* @param contextItem the initial context item, which may be null if no
* context item is required, or if it is to be supplied later
* @return an XPathDynamicContext object representing a suitable dynamic context. This will
* be initialized with a stack frame suitable for holding the variables used by the
* expression.
* @throws XPathException if the context item does not match the required context item type
* set up in the static context
*/
public XPathDynamicContext createDynamicContext(Item contextItem) throws XPathException {
checkContextItemType(contextItem);
XPathContextMajor context = new XPathContextMajor(contextItem, executable);
context.openStackFrame(stackFrameMap);
return new XPathDynamicContext(env.getRequiredContextItemType(), context, stackFrameMap);
}
/**
* Create a dynamic context suitable for evaluating this expression within an environment
* represented by an existing controller. The dynamic context will inherit properties of the
* Controller such as the current error listener, URI resolver, document pool, and implicit
* timezone.
*
* @param controller an existing controller. May be null, in which case the method is
* equivalent to calling {@link #createDynamicContext(net.sf.saxon.om.Item)}
* @param contextItem the initial context item, which may be null if no
* context item is required, or if it is to be supplied later
* @return an XPathDynamicContext object representing a suitable dynamic context. This will
* be initialized with a stack frame suitable for holding the variables used by the
* expression.
* @throws XPathException if the context item does not match the required context item type
* set up in the static context
* @since 9.2
*/
public XPathDynamicContext createDynamicContext(Controller controller, Item contextItem)
throws XPathException {
checkContextItemType(contextItem);
if (controller == null) {
return createDynamicContext(contextItem);
} else {
XPathContextMajor context = controller.newXPathContext();
context.openStackFrame(stackFrameMap);
XPathDynamicContext dc = new XPathDynamicContext(env.getRequiredContextItemType(), context, stackFrameMap);
if (contextItem != null) {
dc.setContextItem(contextItem);
}
return dc;
}
}
private void checkContextItemType(Item contextItem) throws XPathException {
if (contextItem != null) {
ItemType type = env.getRequiredContextItemType();
TypeHierarchy th = env.getConfiguration().getTypeHierarchy();
if (!type.matches(contextItem, th)) {
throw new XPathException("Supplied context item does not match required context item type " +
type);
}
}
}
/**
* Execute the expression, returning the result as a {@link SequenceIterator}, whose members will be instances
* of the class {@link net.sf.saxon.om.Item}
* Note that if evaluation of the expression fails with a dynamic error, this will generally
* be reported in the form of an exception thrown by the next() method of the {@link SequenceIterator}
*
* @param context the XPath dynamic context
* @return an iterator over the result of the expression
* @throws XPathException if a dynamic error occurs during the expression evaluation (though in many
* cases, the error will only be detected when the iterator is actually used).
*/
public SequenceIterator iterate(XPathDynamicContext context) throws XPathException {
context.checkExternalVariables(stackFrameMap, numberOfExternalVariables);
return expression.iterate(context.getXPathContextObject());
}
/**
* Execute the expression, returning the result as a List, whose members will be instances
* of the class {@link net.sf.saxon.om.Item}
*
* @param context the XPath dynamic context
* @return a list of items representing the result of the expression
* @throws XPathException if a dynamic error occurs while evaluation the expression
*/
public List- evaluate(XPathDynamicContext context) throws XPathException {
List
- list = new ArrayList<>(20);
// Don't replace with list::add - C# doesn't like it because list.add() returns boolean
//noinspection Convert2MethodRef
SequenceTool.supply(expression.iterate(context.getXPathContextObject()), (ItemConsumer) item -> list.add(item));
return list;
}
/**
* Execute the expression, returning the result as a single {@link net.sf.saxon.om.Item}
* If the result of the expression is a sequence containing more than one item, items after
* the first are discarded. If the result is an empty sequence, the method returns null.
*
* @param context the XPath dynamic context
* @return the first item in the result of the expression, or null to indicate that the result
* is an empty sequence
* @throws XPathException if a dynamic error occurs during the expression evaluation
*/
/*@Nullable*/
public Item evaluateSingle(XPathDynamicContext context) throws XPathException {
SequenceIterator iter = expression.iterate(context.getXPathContextObject());
Item result = iter.next();
iter.close();
return result;
}
/**
* Evaluate the expression, returning its effective boolean value
*
* @param context the XPath dynamic context
* @return the effective boolean value of the result, as defined by the fn:boolean() function
* @throws XPathException if a dynamic error occurs, or if the result is a value for which
* no effective boolean value is defined
*/
public boolean effectiveBooleanValue(XPathDynamicContext context) throws XPathException {
return expression.effectiveBooleanValue(context.getXPathContextObject());
}
/**
* Low-level method to get the internal Saxon expression object. This exposes a wide range of
* internal methods that may be needed by specialized applications, and allows greater control
* over the dynamic context for evaluating the expression.
*
* @return the underlying Saxon expression object.
*/
public Expression getInternalExpression() {
return expression;
}
}