    001/*
    002 * Copyright (c) 2007-2017 Xplenty, 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
    021package cascading.operation.xml;
    022
    023import javax.xml.parsers.DocumentBuilder;
    024import javax.xml.xpath.XPathConstants;
    025import javax.xml.xpath.XPathExpressionException;
    026
    027import cascading.flow.FlowProcess;
    028import cascading.operation.Function;
    029import cascading.operation.FunctionCall;
    030import cascading.operation.OperationException;
    031import cascading.tuple.Fields;
    032import cascading.tuple.Tuple;
    033import cascading.tuple.TupleEntry;
    034import cascading.util.Pair;
    035import org.slf4j.Logger;
    036import org.slf4j.LoggerFactory;
    037import org.w3c.dom.Document;
    038import 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 */
    044public 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  }