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Commons JXPath example source code file (Expression.java)
The Commons JXPath Expression.java source code/* * 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.apache.commons.jxpath.ri.compiler; import org.apache.commons.jxpath.NodeSet; import org.apache.commons.jxpath.Pointer; import org.apache.commons.jxpath.ri.EvalContext; import org.apache.commons.jxpath.ri.model.NodePointer; import org.apache.commons.jxpath.ri.QName; import org.apache.commons.jxpath.util.ValueUtils; import java.util.Collections; import java.util.Iterator; import java.util.Locale; /** * Common superclass for several types of nodes in the parse tree. Provides * APIs for optimization of evaluation of expressions. Specifically, an * expression only needs to executed once during the evaluation of an xpath * if that expression is context-independent. Expression.isContextDependent() * provides that hint. * * @author Dmitri Plotnikov * @version $Revision: 652845 $ $Date: 2008-05-02 12:46:46 -0500 (Fri, 02 May 2008) $ */ public abstract class Expression { /** zero */ protected static final Double ZERO = new Double(0); /** one */ protected static final Double ONE = new Double(1); /** NaN */ protected static final Double NOT_A_NUMBER = new Double(Double.NaN); private boolean contextDependencyKnown = false; private boolean contextDependent; /** * Returns true if this expression should be re-evaluated * each time the current position in the context changes. * @return boolean */ public synchronized boolean isContextDependent() { if (!contextDependencyKnown) { contextDependent = computeContextDependent(); contextDependencyKnown = true; } return contextDependent; } /** * Implemented by subclasses and result is cached by isContextDependent() * @return calculated context-dependentness as boolean */ public abstract boolean computeContextDependent(); /** * Evaluates the expression. If the result is a node set, returns * the first element of the node set. * @param context evaluation context * @return Object */ public abstract Object computeValue(EvalContext context); /** * Evaluates the expression. If the result is a node set, returns * the first element of the node set. * @param context evaluation context * @return Object */ public abstract Object compute(EvalContext context); /** * Iterate over the values from the specified context. * @param context evaluation context * @return value Iterator */ public Iterator iterate(EvalContext context) { Object result = compute(context); if (result instanceof EvalContext) { return new ValueIterator((EvalContext) result); } if (result instanceof NodeSet) { return new ValueIterator(((NodeSet) result).getPointers().iterator()); } return ValueUtils.iterate(result); } /** * Iterate over the pointers from the specified context. * @param context evaluation context * @return pointer Iterator */ public Iterator iteratePointers(EvalContext context) { Object result = compute(context); if (result == null) { return Collections.EMPTY_LIST.iterator(); } if (result instanceof EvalContext) { return (EvalContext) result; } if (result instanceof NodeSet) { return new PointerIterator(((NodeSet) result).getPointers().iterator(), new QName(null, "value"), context.getRootContext().getCurrentNodePointer().getLocale()); } return new PointerIterator(ValueUtils.iterate(result), new QName(null, "value"), context.getRootContext().getCurrentNodePointer().getLocale()); } /** * Pointer iterator */ public static class PointerIterator implements Iterator { private Iterator iterator; private QName qname; private Locale locale; //to what method does the following comment refer? /** * Create a new PointerIterator * @param it underlying Iterator * @param qname name * @param locale Locale * @deprecated Use the method that takes a NamespaceManager */ public PointerIterator(Iterator it, QName qname, Locale locale) { this.iterator = it; this.qname = qname; this.locale = locale; } public boolean hasNext() { return iterator.hasNext(); } public Object next() { Object o = iterator.next(); return o instanceof Pointer ? o : NodePointer.newNodePointer(qname, o, locale); } /** * Unsupported. */ public void remove() { throw new UnsupportedOperationException(); } } /** * Value Iterator */ public static class ValueIterator implements Iterator { private Iterator iterator; /** * Create a new ValueIterator. * @param it underlying Iterator, may contain pointers */ public ValueIterator(Iterator it) { this.iterator = it; } public boolean hasNext() { return iterator.hasNext(); } public Object next() { Object o = iterator.next(); return o instanceof Pointer ? ((Pointer) o).getValue() : o; } /** * Unsupported. */ public void remove() { throw new UnsupportedOperationException(); } } } Other Commons JXPath examples (source code examples)Here is a short list of links related to this Commons JXPath Expression.java source code file: |
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