/*
* Copyright (c) 2007-2014 Concurrent, Inc. All Rights Reserved.
*
* Project and contact information: http://www.cascading.org/
*
* This file is part of the Cascading project.
*
* 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.
*/
package cascading.operation.xml;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpressionException;
import cascading.flow.FlowProcess;
import cascading.operation.Function;
import cascading.operation.FunctionCall;
import cascading.operation.OperationException;
import cascading.tuple.Fields;
import cascading.tuple.Tuple;
import cascading.util.Pair;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
/**
* XPathParser will extract a value from the passed Tuple argument into a new Tuple field. One field
* for every given XPath expression will be created. This function effectively converts an XML document into
* a table.
* <p/>
* If the returned value of the expression is a NodeList, only the first Node is used. The Node is converted to a new
* XML document and converted to a String. If only the text values are required, search on the text() nodes, or consider
* using {@link XPathGenerator} to handle multiple NodeList values.
*/
public class XPathParser extends XPathOperation implements Function<Pair<DocumentBuilder, Tuple>>
{
/** Field LOG */
private static final Logger LOG = LoggerFactory.getLogger( XPathParser.class );
/**
* Constructor XPathParser creates a new XPathParser instance.
*
* @param fieldDeclaration of type Fields
* @param namespaces of type String[][]
* @param paths of type String...
*/
public XPathParser( Fields fieldDeclaration, String[][] namespaces, String... paths )
{
super( 1, fieldDeclaration, namespaces, paths );
if( !fieldDeclaration.isSubstitution() && fieldDeclaration.size() != paths.length )
throw new IllegalArgumentException( "declared fields and given xpath expressions are not the same size: " + fieldDeclaration.print() + " paths: " + paths.length );
}
/**
* Constructor XPathParser creates a new XPathParser instance.
*
* @param fieldDeclaration of type Fields
* @param paths of type String...
*/
public XPathParser( Fields fieldDeclaration, String... paths )
{
super( 1, fieldDeclaration, null, paths );
if( !fieldDeclaration.isSubstitution() && fieldDeclaration.size() != paths.length )
throw new IllegalArgumentException( "declared fields and given xpath expressions are not the same size: " + fieldDeclaration.print() + " paths: " + paths.length );
}
@Override
public void operate( FlowProcess flowProcess, FunctionCall<Pair<DocumentBuilder, Tuple>> functionCall )
{
Tuple tuple = functionCall.getContext().getRhs();
tuple.clear();
String argument = functionCall.getArguments().getString( 0 );
Document document = parseDocument( functionCall.getContext().getLhs(), argument );
for( int i = 0; i < getExpressions().size(); i++ )
{
try
{
NodeList value = (NodeList) getExpressions().get( i ).evaluate( document, XPathConstants.NODESET );
if( LOG.isDebugEnabled() )
LOG.debug( "xpath: {} was: {}", paths[ i ], value != null && value.getLength() != 0 );
if( value != null && value.getLength() != 0 )
tuple.add( writeAsXML( value.item( 0 ) ) );
else
tuple.add( "" );
}
catch( XPathExpressionException exception )
{
throw new OperationException( "could not evaluate xpath expression: " + paths[ i ], exception );
}
}
functionCall.getOutputCollector().add( tuple );
}
}