PipelineStageWriter.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.hadoop.chukwa.datacollection.writer;


import java.util.ArrayList;
import java.util.List;
import org.apache.hadoop.chukwa.Chunk;
import org.apache.hadoop.conf.Configuration;
import org.apache.log4j.Logger;

/**
 * A pipeline of Pipelineable writers
 * Controlled by option 'chukwaCollector.pipeline', which should be a comma-
 * separated list of classnames. 
 * 
 */
public class PipelineStageWriter implements ChukwaWriter {
  Logger log = Logger.getLogger(PipelineStageWriter.class);

  ChukwaWriter writer; // head of pipeline

  @Override
  public CommitStatus add(List<Chunk> chunks) throws WriterException {
    return writer.add(chunks);
  }

  @Override
  public void close() throws WriterException {
    writer.close();
  }

  @Override
  public void init(Configuration conf) throws WriterException {
    if (conf.get("chukwaCollector.pipeline") != null) {
      String pipeline = conf.get("chukwaCollector.pipeline");
      try {
        String[] classes = pipeline.split(",");
        log.info("using pipelined writers, pipe length is " + classes.length);
        PipelineableWriter lastWriter = null;
        if (classes.length > 1) {
          lastWriter = (PipelineableWriter) conf.getClassByName(classes[0])
              .newInstance();
          lastWriter.init(conf);
          writer = lastWriter;
        }

        for (int i = 1; i < classes.length - 1; ++i) {
          Class<?> stageClass = conf.getClassByName(classes[i]);
          Object st = stageClass.newInstance();
          if (!(st instanceof PipelineableWriter))
            log.error("class " + classes[i]
                + " in processing pipeline isn't a pipeline stage");

          PipelineableWriter stage = (PipelineableWriter) stageClass
              .newInstance();
          stage.init(conf);
          // throws exception if types don't match or class not found; this is
          // OK.

          lastWriter.setNextStage(stage);
          lastWriter = stage;
        }
        Class<?> stageClass = conf.getClassByName(classes[classes.length - 1]);
        Object st = stageClass.newInstance();

        if (!(st instanceof ChukwaWriter)) {
          log.error("class " + classes[classes.length - 1]
              + " at end of processing pipeline isn't a ChukwaWriter");
          throw new WriterException("bad pipeline");
        } else {
          ((ChukwaWriter)st).init(conf);
          if (lastWriter != null)
            lastWriter.setNextStage((ChukwaWriter) st);
          else
            writer = (ChukwaWriter) st; // one stage pipeline
        }
        return;
      } catch (Exception e) {
        // if anything went wrong (missing class, etc) we wind up here.
        log.error("failed to set up pipeline, defaulting to SeqFileWriter", e);
        // fall through to default case
        throw new WriterException("bad pipeline");
      }
    } else {
      throw new WriterException("must set chukwaCollector.pipeline");
    }
  }

}