HashSumEventStream.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreemnets.  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 opennlp.model;

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.math.BigInteger;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

import opennlp.model.Event;
import opennlp.model.EventStream;

public class HashSumEventStream implements EventStream {

  private final EventStream eventStream;
  
  private MessageDigest digest;
  
  public HashSumEventStream(EventStream eventStream) {
    this.eventStream = eventStream;
    
    try {
      digest = MessageDigest.getInstance("MD5");
    } catch (NoSuchAlgorithmException e) {
      // should never happen, does all java runtimes have md5 ?!
     throw new IllegalStateException(e);
    }
  }
  
  public boolean hasNext() throws IOException {
    return eventStream.hasNext();
  }

  public Event next() throws IOException {
    
    Event event = eventStream.next();
    
    try {
      digest.update(event.toString().getBytes("UTF-8"));
    }
    catch (UnsupportedEncodingException e) {
      throw new IllegalStateException("UTF-8 encoding is not available!");
    }
    
    return event;
  }
  
  /**
   * Calculates the hash sum of the stream. The method must be
   * called after the stream is completely consumed.
   * 
   * @return the hash sum
   * @throws IllegalStateException if the stream is not consumed completely,
   * completely means that hasNext() returns false
   */
  public BigInteger calculateHashSum() {
    
//    if (hasNext())
//      throw new IllegalStateException("stream must be consumed completely!");
    
    return new BigInteger(1, digest.digest());
  }
  
  public void remove() {
  }
}