org.apache.xpath.Expression Maven / Gradle / Ivy
/*
* 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.
*/
/*
* $Id: Expression.java 468655 2006-10-28 07:12:06Z minchau $
*/
package org.apache.xpath;
import javax.xml.transform.ErrorListener;
import javax.xml.transform.TransformerException;
import org.apache.xalan.res.XSLMessages;
import org.apache.xml.dtm.DTM;
import org.apache.xml.dtm.DTMIterator;
import org.apache.xml.utils.XMLString;
import org.apache.xpath.objects.XNodeSet;
import org.apache.xpath.objects.XObject;
import org.apache.xpath.res.XPATHErrorResources;
import org.xml.sax.ContentHandler;
/**
* This abstract class serves as the base for all expression objects. An
* Expression can be executed to return a {@link org.apache.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 java.io.Serializable, ExpressionNode, XPathVisitable
{
static final long serialVersionUID = 565665869777906902L;
/**
* 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;
}
// /**
// * Set the location where this expression was built from.
// *
// *
// * @param locator the location where this expression was built from, may be
// * null.
// */
// public void setSourceLocator(SourceLocator locator)
// {
// m_slocator = locator;
// }
/**
* 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(XPathContext xctxt, 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(
XPathContext xctxt, int currentNode, DTM dtm, 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(XPathContext xctxt, 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
*/
public double num(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
*/
public boolean bool(XPathContext xctxt)
throws javax.xml.transform.TransformerException
{
return execute(xctxt).bool();
}
/**
* Cast result object to a string.
*
*
* @param xctxt The XPath runtime context.
* @return The string this wraps or the empty string if null
*
* @throws javax.xml.transform.TransformerException
*/
public XMLString xstr(XPathContext xctxt)
throws javax.xml.transform.TransformerException
{
return execute(xctxt).xstr();
}
/**
* Tell if the expression is a nodeset expression. In other words, tell
* if you can execute {@link #asNode(XPathContext) asNode} without an exception.
* @return true if the expression can be represented as a nodeset.
*/
public boolean isNodesetExpr()
{
return false;
}
/**
* 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
*/
public int asNode(XPathContext xctxt)
throws javax.xml.transform.TransformerException
{
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
* @xsl.usage experimental
*/
public DTMIterator asIterator(XPathContext xctxt, int contextNode)
throws javax.xml.transform.TransformerException
{
try
{
xctxt.pushCurrentNodeAndExpression(contextNode, contextNode);
return execute(xctxt).iter();
}
finally
{
xctxt.popCurrentNodeAndExpression();
}
}
/**
* Given an select expression and a context, evaluate the XPath
* and return the resulting iterator, but do not clone.
*
* @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
* @xsl.usage experimental
*/
public DTMIterator asIteratorRaw(XPathContext xctxt, int contextNode)
throws javax.xml.transform.TransformerException
{
try
{
xctxt.pushCurrentNodeAndExpression(contextNode, contextNode);
XNodeSet nodeset = (XNodeSet)execute(xctxt);
return nodeset.iterRaw();
}
finally
{
xctxt.popCurrentNodeAndExpression();
}
}
/**
* Execute an expression in the XPath runtime context, and return the
* result of the expression.
*
*
* @param xctxt The XPath runtime context.
* NEEDSDOC @param handler
*
* @return The result of the expression in the form of a XObject.
*
* @throws javax.xml.transform.TransformerException if a runtime exception
* occurs.
* @throws org.xml.sax.SAXException
*/
public void executeCharsToContentHandler(
XPathContext xctxt, ContentHandler handler)
throws javax.xml.transform.TransformerException,
org.xml.sax.SAXException
{
XObject obj = execute(xctxt);
obj.dispatchCharactersEvents(handler);
obj.detach();
}
/**
* 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;
}
/**
* This function is used to fixup variables from QNames to stack frame
* indexes at stylesheet build time.
* @param vars List of QNames that correspond to variables. This list
* should be searched backwards for the first qualified name that
* corresponds to the variable reference qname. The position of the
* QName in the vector from the start of the vector will be its position
* in the stack frame (but variables above the globalsTop value will need
* to be offset to the current stack frame).
* NEEDSDOC @param globalsSize
*/
public abstract void fixupVariables(java.util.Vector vars, int globalsSize);
/**
* 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(Expression expr)
{
if(null == expr)
return false;
return (getClass() == expr.getClass());
}
/**
* Warn the user of an problem.
*
* @param xctxt The XPath runtime context.
* @param msg An error msgkey that corresponds to one of the conststants found
* in {@link org.apache.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
*/
public void warn(XPathContext xctxt, String msg, Object[] args)
throws javax.xml.transform.TransformerException
{
java.lang.String fmsg = XSLMessages.createXPATHWarning(msg, args);
if (null != xctxt)
{
ErrorListener eh = xctxt.getErrorListener();
// TO DO: Need to get stylesheet Locator from here.
eh.warning(new TransformerException(fmsg, xctxt.getSAXLocator()));
}
}
/**
* 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.
*
* @throws javax.xml.transform.TransformerException
*/
public void assertion(boolean b, java.lang.String msg)
{
if (!b)
{
java.lang.String fMsg = XSLMessages.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.apache.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
*/
public void error(XPathContext xctxt, String msg, Object[] args)
throws javax.xml.transform.TransformerException
{
java.lang.String fmsg = XSLMessages.createXPATHMessage(msg, args);
if (null != xctxt)
{
ErrorListener eh = xctxt.getErrorListener();
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 ================
/** This pair of methods are used to inform the node of its
parent. */
public void exprSetParent(ExpressionNode n)
{
assertion(n != this, "Can not parent an expression to itself!");
m_parent = n;
}
public ExpressionNode exprGetParent()
{
return m_parent;
}
/** This method tells the node to add its argument to the node's
list of children. */
public void exprAddChild(ExpressionNode n, int i)
{
assertion(false, "exprAddChild method not implemented!");
}
/** This method returns a child node. The children are numbered
from zero, left to right. */
public ExpressionNode exprGetChild(int i)
{
return null;
}
/** Return the number of children the node has. */
public int exprGetNumChildren()
{
return 0;
}
//=============== SourceLocator methods ================
/**
* Return the public identifier for the current document event.
*
* The return value is the public identifier of the document
* entity or of the external parsed entity in which the markup that
* triggered the event appears.
*
* @return A string containing the public identifier, or
* null if none is available.
* @see #getSystemId
*/
public String getPublicId()
{
if(null == m_parent)
return null;
return m_parent.getPublicId();
}
/**
* Return the system identifier for the current document event.
*
* The return value is the system identifier of the document
* entity or of the external parsed entity in which the markup that
* triggered the event appears.
*
* If the system identifier is a URL, the parser must resolve it
* fully before passing it to the application.
*
* @return A string containing the system identifier, or null
* if none is available.
* @see #getPublicId
*/
public String getSystemId()
{
if(null == m_parent)
return null;
return m_parent.getSystemId();
}
/**
* Return the line number where the current document event ends.
*
* Warning: The return value from the method
* is intended only as an approximation for the sake of error
* reporting; it is not intended to provide sufficient information
* to edit the character content of the original XML document.
*
* The return value is an approximation of the line number
* in the document entity or external parsed entity where the
* markup that triggered the event appears.
*
* @return The line number, or -1 if none is available.
* @see #getColumnNumber
*/
public int getLineNumber()
{
if(null == m_parent)
return 0;
return m_parent.getLineNumber();
}
/**
* Return the character position where the current document event ends.
*
* Warning: The return value from the method
* is intended only as an approximation for the sake of error
* reporting; it is not intended to provide sufficient information
* to edit the character content of the original XML document.
*
* The return value is an approximation of the column number
* in the document entity or external parsed entity where the
* markup that triggered the event appears.
*
* @return The column number, or -1 if none is available.
* @see #getLineNumber
*/
public int getColumnNumber()
{
if(null == m_parent)
return 0;
return m_parent.getColumnNumber();
}
}