samoa-api/src/main/java/org/apache/samoa/topology/LocalEntranceProcessingItem.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 org.apache.samoa.topology;

import org.apache.samoa.core.ContentEvent;
import org.apache.samoa.core.EntranceProcessor;

/**
 * Implementation of EntranceProcessingItem for local engines (Simple, Multithreads)
 * 
 * @author Anh Thu Vu
 * 
 */
public class LocalEntranceProcessingItem extends AbstractEntranceProcessingItem {
  public LocalEntranceProcessingItem(EntranceProcessor processor) {
    super(processor);
  }

  /**
   * If there are available events, first event in the queue will be sent out on the output stream.
   * 
   * @return true if there is (at least) one available event and it was sent out false otherwise
   */
  public boolean injectNextEvent() {
    if (this.getProcessor().hasNext()) {
      ContentEvent event = this.getProcessor().nextEvent();
      this.getOutputStream().put(event);
      return true;
    }
    return false;
  }

  /**
   * Start sending events by calling {@link #injectNextEvent()}. If there are no available events, and that the stream
   * is not entirely consumed, it will wait by calling {@link #waitForNewEvents()} before attempting to send again. </p>
   * When the stream is entirely consumed, the last event is tagged accordingly and the processor gets the finished
   * status.
   * 
   */
  public void startSendingEvents() {
    if (this.getOutputStream() == null)
      throw new IllegalStateException("Try sending events from EntrancePI while outputStream is not set.");

    while (!this.getProcessor().isFinished()) {
      if (!this.injectNextEvent()) {
        try {
          waitForNewEvents();
        } catch (Exception e) {
          e.printStackTrace();
          break;
        }
      }
    }
  }

  /**
   * Method to wait for an amount of time when there are no available events. Implementation of EntranceProcessingItem
   * should override this method to implement non-blocking wait or to adjust the amount of time.
   */
  protected void waitForNewEvents() throws Exception {
    Thread.sleep(100);
  }
}