iomapperbase.java

hadoop:Nutch集群平台

package org.apache.hadoop.fs;

import java.io.IOException;
import java.net.InetAddress;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.UTF8;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.io.WritableComparable;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.Mapper;
import org.apache.hadoop.mapred.OutputCollector;
import org.apache.hadoop.mapred.Reporter;

/**
 * Base mapper class for IO operations.
 * <p>
 * Two abstract method {@link #doIO(Reporter,String,long)} and 
 * {@link #collectStats(OutputCollector,String,long,Object)} should be
 * overloaded in derived classes to define the IO operation and the
 * statistics data to be collected by subsequent reducers.
 * 
 * @author Konstantin Shvachko
 */
public abstract class IOMapperBase extends Configured implements Mapper {
  protected byte[] buffer;
  protected int bufferSize;
  protected FileSystem fs;
  protected String hostName;

  public IOMapperBase(Configuration conf) { 
    super(conf); 
    try {
      fs = FileSystem.get(conf);
    } catch (Exception e) {
      throw new RuntimeException( "Cannot create file system.", e );
    }
    bufferSize = conf.getInt("test.io.file.buffer.size", 4096);
    buffer = new byte[bufferSize];
    try {
      hostName = InetAddress.getLocalHost().getHostName();
    } catch(Exception e) {
      hostName = "localhost";
    }
  }

  public void configure(JobConf job) {
    setConf(job);
  }

  public void close() throws IOException {
  }
  
  /**
   * Perform io operation, usually read or write.
   * 
   * @param reporter
   * @param name file name
   * @param value offset within the file
   * @return object that is passed as a parameter to 
   *          {@link #collectStats(OutputCollector,String,long,Object)}
   * @throws IOException
   */
  abstract Object doIO( Reporter reporter, 
                        String name, 
                        long value ) throws IOException;

  /**
   * Collect stat data to be combined by a subsequent reducer.
   * 
   * @param output
   * @param name file name
   * @param execTime IO execution time
   * @param doIOReturnValue value returned by {@link #doIO(Reporter,String,long)}
   * @throws IOException
   */
  abstract void collectStats( OutputCollector output, 
                              String name, 
                              long execTime, 
                              Object doIOReturnValue ) throws IOException;
  
  /**
   * Map file name and offset into statistical data.
   * <p>
   * The map task is to get the 
   * <tt>key</tt>, which contains the file name, and the 
   * <tt>value</tt>, which is the offset within the file.
   * 
   * The parameters are passed to the abstract method 
   * {@link #doIO(Reporter,String,long)}, which performs the io operation, 
   * usually read or write data, and then 
   * {@link #collectStats(OutputCollector,String,long,Object)} 
   * is called to prepare stat data for a subsequent reducer.
   */
  public void map(WritableComparable key, 
                  Writable value,
                  OutputCollector output, 
                  Reporter reporter) throws IOException {
    String name = ((UTF8)key).toString();
    long longValue = ((LongWritable)value).get();
    
    reporter.setStatus("starting " + name + " ::host = " + hostName);
    
    long tStart = System.currentTimeMillis();
    Object statValue = doIO( reporter, name, longValue );
    long tEnd = System.currentTimeMillis();
    long execTime = tEnd - tStart;
    collectStats( output, name, execTime, statValue );
    
    reporter.setStatus("finished " + name + " ::host = " + hostName);
  }
}