library/src/main/java/org/apache/apex/malhar/lib/xml/AbstractXmlDOMOperator.java

/**
 * 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 com.datatorrent.lib.xml;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;

import org.w3c.dom.Document;
import org.xml.sax.InputSource;

import com.datatorrent.api.Context;
import com.datatorrent.api.DefaultInputPort;
import com.datatorrent.common.util.BaseOperator;
import com.datatorrent.netlet.util.DTThrowable;

/**
 * This is the base implementation for an xml operator,
 * which parses incoming tuples using the Java XML DOM parser. 
 * Subclasses must implement the methods which are use to process the parsed XML.
 * <p></p>
 * @displayName Abstract XML DOM
 * @category XML
 * @tags abstract, xml, dom
 *
 * @since 1.0.2
 */
@org.apache.hadoop.classification.InterfaceStability.Evolving
public abstract class AbstractXmlDOMOperator<T> extends BaseOperator
{
  protected transient DocumentBuilderFactory docFactory;
  protected transient DocumentBuilder docBuilder;

  @Override
  public void setup(Context.OperatorContext context)
  {
    try {
      docFactory = DocumentBuilderFactory.newInstance();
      docBuilder = docFactory.newDocumentBuilder();
    } catch (ParserConfigurationException e) {
      throw new RuntimeException(e);
    }
  }

  /**
   * This port receives the tuples which will be parsed as xml.
   */
  public transient DefaultInputPort<T> input = new DefaultInputPort<T>()
  {
    @Override
    public void process(T tuple)
    {
      processTuple(tuple);
    }
  };

  protected void processTuple(T tuple)
  {
    try {
      InputSource source = getInputSource(tuple);
      Document document = docBuilder.parse(source);
      processDocument(document, tuple);
    } catch (Exception e) {
      DTThrowable.rethrow(e);
    }
  }

  protected abstract InputSource getInputSource(T tuple);

  protected abstract void processDocument(Document document, T tuple);

}