    001    /*
    002     * Copyright (c) 2007-2014 Concurrent, Inc. All Rights Reserved.
    003     *
    004     * Project and contact information: http://www.cascading.org/
    005     *
    006     * This file is part of the Cascading project.
    007     *
    008     * Licensed under the Apache License, Version 2.0 (the "License");
    009     * you may not use this file except in compliance with the License.
    010     * You may obtain a copy of the License at
    011     *
    012     *     http://www.apache.org/licenses/LICENSE-2.0
    013     *
    014     * Unless required by applicable law or agreed to in writing, software
    015     * distributed under the License is distributed on an "AS IS" BASIS,
    016     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    017     * See the License for the specific language governing permissions and
    018     * limitations under the License.
    019     */
    020
    021    package cascading.operation.xml;
    022
    023    import javax.xml.parsers.DocumentBuilder;
    024    import javax.xml.xpath.XPathConstants;
    025    import javax.xml.xpath.XPathExpressionException;
    026
    027    import cascading.flow.FlowProcess;
    028    import cascading.operation.Function;
    029    import cascading.operation.FunctionCall;
    030    import cascading.operation.OperationException;
    031    import cascading.tuple.Fields;
    032    import cascading.tuple.Tuple;
    033    import cascading.tuple.TupleEntry;
    034    import cascading.util.Pair;
    035    import org.slf4j.Logger;
    036    import org.slf4j.LoggerFactory;
    037    import org.w3c.dom.Document;
    038    import org.w3c.dom.NodeList;
    039
    040    /**
    041     * XPathGenerator is a Generator function that will emit a new Tuple for every Node returned by
    042     * the given XPath expression.
    043     */
    044    public class XPathGenerator extends XPathOperation implements Function<Pair<DocumentBuilder, Tuple>>
    045      {
    046      /** Field LOG */
    047      private static final Logger LOG = LoggerFactory.getLogger( XPathGenerator.class );
    048
    049      /**
    050       * Constructor XPathGenerator creates a new XPathGenerator instance.
    051       *
    052       * @param fieldDeclaration of type Fields
    053       * @param namespaces       of type String[][]
    054       * @param paths            of type String...
    055       */
    056      public XPathGenerator( Fields fieldDeclaration, String[][] namespaces, String... paths )
    057        {
    058        super( 1, fieldDeclaration, namespaces, paths );
    059
    060        if( fieldDeclaration.size() != 1 )
    061          throw new IllegalArgumentException( "only one field can be declared: " + fieldDeclaration.print() );
    062
    063        }
    064
    065      @Override
    066      public void operate( FlowProcess flowProcess, FunctionCall<Pair<DocumentBuilder, Tuple>> functionCall )
    067        {
    068        TupleEntry input = functionCall.getArguments();
    069
    070        if( input.getObject( 0 ) == null || !( input.getObject( 0 ) instanceof String ) )
    071          return;
    072
    073        String value = input.getString( 0 );
    074
    075        if( value.length() == 0 ) // intentionally not trim()ing this value
    076          return;
    077
    078        Document document = parseDocument( functionCall.getContext().getLhs(), value );
    079
    080        for( int i = 0; i < getExpressions().size(); i++ )
    081          {
    082          try
    083            {
    084            NodeList nodeList = (NodeList) getExpressions().get( i ).evaluate( document, XPathConstants.NODESET );
    085
    086            if( LOG.isDebugEnabled() )
    087              LOG.debug( "xpath: {} was: {}", paths[ i ], nodeList != null && nodeList.getLength() != 0 );
    088
    089            if( nodeList == null )
    090              continue;
    091
    092            for( int j = 0; j < nodeList.getLength(); j++ )
    093              {
    094              functionCall.getContext().getRhs().set( 0, writeAsXML( nodeList.item( j ) ) );
    095              functionCall.getOutputCollector().add( functionCall.getContext().getRhs() );
    096              }
    097
    098            }
    099          catch( XPathExpressionException exception )
    100            {
    101            throw new OperationException( "could not evaluate xpath expression: " + paths[ i ], exception );
    102            }
    103          }
    104        }
    105      }