expression.java

java1.6众多例子参考

/*
 * Copyright 1999-2004 The Apache Software Foundation.
 *
 * Licensed 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,v 1.2.4.2 2005/09/14 19:50:20 jeffsuttor Exp $
 */
package com.sun.org.apache.xpath.internal;

import javax.xml.transform.ErrorListener;
import javax.xml.transform.TransformerException;

import com.sun.org.apache.xalan.internal.res.XSLMessages;
import com.sun.org.apache.xml.internal.dtm.DTM;
import com.sun.org.apache.xml.internal.dtm.DTMIterator;
import com.sun.org.apache.xml.internal.utils.XMLString;
import com.sun.org.apache.xpath.internal.objects.XNodeSet;
import com.sun.org.apache.xpath.internal.objects.XObject;
import com.sun.org.apache.xpath.internal.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 com.sun.org.apache.xpath.internal.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 <code>XObject</code>.
   *
   * @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 <code>XObject</code>.
   *
   * @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 <code>XObject</code>.
   *
   * @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 <code>XObject</code>.
   *
   * @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.
   *