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The XPath engine used by HtmlUnit.
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.htmlunit.xpath;
import javax.xml.transform.ErrorListener;
import javax.xml.transform.TransformerException;
import org.htmlunit.xpath.objects.XObject;
import org.htmlunit.xpath.res.XPATHErrorResources;
import org.htmlunit.xpath.res.XPATHMessages;
import org.htmlunit.xpath.xml.dtm.DTM;
import org.htmlunit.xpath.xml.dtm.DTMIterator;
/**
* This abstract class serves as the base for all expression objects. An Expression can be executed
* to return a {@link org.htmlunit.xpath.objects.XObject}, normally has a location within a document
* or DOM, can send error and warning events, and normally do not hold state and are meant to be
* immutable once construction has completed. An exception to the immutibility rule is iterators and
* walkers, which must be cloned in order to be used -- the original must still be immutable.
*/
public abstract class Expression implements ExpressionNode, XPathVisitable {
/**
* The location where this expression was built from. Need for diagnostic messages. May be null.
*
* @serial
*/
private ExpressionNode m_parent;
/**
* Tell if this expression or it's subexpressions can traverse outside the current subtree.
*
* @return true if traversal outside the context node's subtree can occur.
*/
public boolean canTraverseOutsideSubtree() {
return false;
}
/**
* Execute an expression in the XPath runtime context, and return the result of the expression.
*
* @param xctxt The XPath runtime context.
* @param currentNode The currentNode.
* @return The result of the expression in the form of a XObject.
* @throws javax.xml.transform.TransformerException if a runtime exception occurs.
*/
public XObject execute(final XPathContext xctxt, final int currentNode)
throws javax.xml.transform.TransformerException {
// For now, the current node is already pushed.
return execute(xctxt);
}
/**
* Execute an expression in the XPath runtime context, and return the result of the expression.
*
* @param xctxt The XPath runtime context.
* @param currentNode The currentNode.
* @param dtm The DTM of the current node.
* @param expType The expanded type ID of the current node.
* @return The result of the expression in the form of a XObject.
* @throws javax.xml.transform.TransformerException if a runtime exception occurs.
*/
public XObject execute(
final XPathContext xctxt, final int currentNode, final DTM dtm, final int expType)
throws javax.xml.transform.TransformerException {
// For now, the current node is already pushed.
return execute(xctxt);
}
/**
* Execute an expression in the XPath runtime context, and return the result of the expression.
*
* @param xctxt The XPath runtime context.
* @return The result of the expression in the form of a XObject.
* @throws javax.xml.transform.TransformerException if a runtime exception occurs.
*/
public abstract XObject execute(XPathContext xctxt)
throws javax.xml.transform.TransformerException;
/**
* Execute an expression in the XPath runtime context, and return the result of the expression,
* but tell that a "safe" object doesn't have to be returned. The default implementation just
* calls execute(xctxt).
*
* @param xctxt The XPath runtime context.
* @param destructiveOK true if a "safe" object doesn't need to be returned.
* @return The result of the expression in the form of a XObject.
* @throws javax.xml.transform.TransformerException if a runtime exception occurs.
*/
public XObject execute(final XPathContext xctxt, final boolean destructiveOK)
throws javax.xml.transform.TransformerException {
return execute(xctxt);
}
/**
* Evaluate expression to a number.
*
* @param xctxt The XPath runtime context.
* @return The expression evaluated as a double.
* @throws javax.xml.transform.TransformerException if any
*/
public double num(final XPathContext xctxt) throws javax.xml.transform.TransformerException {
return execute(xctxt).num();
}
/**
* Evaluate expression to a boolean.
*
* @param xctxt The XPath runtime context.
* @return false
* @throws javax.xml.transform.TransformerException if any
*/
public boolean bool(final XPathContext xctxt) throws javax.xml.transform.TransformerException {
return execute(xctxt).bool();
}
/**
* Return the first node out of the nodeset, if this expression is a nodeset expression.
*
* @param xctxt The XPath runtime context.
* @return the first node out of the nodeset, or DTM.NULL.
* @throws javax.xml.transform.TransformerException if any
*/
public int asNode(final XPathContext xctxt) throws javax.xml.transform.TransformerException {
final DTMIterator iter = execute(xctxt).iter();
return iter.nextNode();
}
/**
* Given an select expression and a context, evaluate the XPath and return the resulting iterator.
*
* @param xctxt The execution context.
* @param contextNode The node that "." expresses.
* @return A valid DTMIterator.
* @throws TransformerException thrown if the active ProblemListener decides the error condition
* is severe enough to halt processing.
* @throws javax.xml.transform.TransformerException if any
*/
public DTMIterator asIterator(final XPathContext xctxt, final int contextNode)
throws javax.xml.transform.TransformerException {
try {
xctxt.pushCurrentNodeAndExpression(contextNode);
return execute(xctxt).iter();
}
finally {
xctxt.popCurrentNodeAndExpression();
}
}
/**
* Tell if this expression returns a stable number that will not change during iterations within
* the expression. This is used to determine if a proximity position predicate can indicate that
* no more searching has to occur.
*
* @return true if the expression represents a stable number.
*/
public boolean isStableNumber() {
return false;
}
/**
* Compare this object with another object and see if they are equal, include the sub heararchy.
*
* @param expr Another expression object.
* @return true if this objects class and the expr object's class are the same, and the data
* contained within both objects are considered equal.
*/
public abstract boolean deepEquals(Expression expr);
/**
* This is a utility method to tell if the passed in class is the same class as this. It is to be
* used by the deepEquals method. I'm bottlenecking it here because I'm not totally confident that
* comparing the class objects is the best way to do this.
*
* @return true of the passed in class is the exact same class as this class.
*/
protected final boolean isSameClass(final Expression expr) {
if (null == expr) {
return false;
}
return getClass() == expr.getClass();
}
/**
* Tell the user of an assertion error, and probably throw an exception.
*
* @param b If false, a runtime exception will be thrown.
* @param msg The assertion message, which should be informative.
* @throws RuntimeException if the b argument is false.
*/
public void assertion(final boolean b, final String msg) {
if (!b) {
final String fMsg =
XPATHMessages.createXPATHMessage(
XPATHErrorResources.ER_INCORRECT_PROGRAMMER_ASSERTION, new Object[] {msg});
throw new RuntimeException(fMsg);
}
}
/**
* Tell the user of an error, and probably throw an exception.
*
* @param xctxt The XPath runtime context.
* @param msg An error msgkey that corresponds to one of the constants found in {@link
* org.htmlunit.xpath.res.XPATHErrorResources}, which is a key for a format string.
* @param args An array of arguments represented in the format string, which may be null.
* @throws TransformerException if the current ErrorListoner determines to throw an exception.
* @throws javax.xml.transform.TransformerException if any
*/
public void error(final XPathContext xctxt, final String msg, final Object[] args)
throws javax.xml.transform.TransformerException {
final String fmsg = XPATHMessages.createXPATHMessage(msg, args);
if (null != xctxt) {
final ErrorListener eh = xctxt.getErrorListener();
final TransformerException te = new TransformerException(fmsg, this);
eh.fatalError(te);
}
}
/**
* Get the first non-Expression parent of this node.
*
* @return null or first ancestor that is not an Expression.
*/
public ExpressionNode getExpressionOwner() {
ExpressionNode parent = exprGetParent();
while ((null != parent) && (parent instanceof Expression)) {
parent = parent.exprGetParent();
}
return parent;
}
// =============== ExpressionNode methods ================
/** {@inheritDoc} */
@Override
public void exprSetParent(final ExpressionNode n) {
assertion(n != this, "Can not parent an expression to itself!");
m_parent = n;
}
/** {@inheritDoc} */
@Override
public ExpressionNode exprGetParent() {
return m_parent;
}
/** {@inheritDoc} */
@Override
public String getPublicId() {
if (null == m_parent) {
return null;
}
return m_parent.getPublicId();
}
/** {@inheritDoc} */
@Override
public String getSystemId() {
if (null == m_parent) {
return null;
}
return m_parent.getSystemId();
}
/** {@inheritDoc} */
@Override
public int getLineNumber() {
if (null == m_parent) {
return 0;
}
return m_parent.getLineNumber();
}
/** {@inheritDoc} */
@Override
public int getColumnNumber() {
if (null == m_parent) {
return 0;
}
return m_parent.getColumnNumber();
}
}
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