nfsdataoutputstream.java

爬虫数据的改进,并修正了一些bug

/* Copyright (c) 2004 The Nutch Organization.  All rights reserved.   */
/* Use subject to the conditions in http://www.nutch.org/LICENSE.txt. */
package net.nutch.fs;

import java.io.*;
import net.nutch.util.NutchConf;

/** Utility that wraps a {@link NFSOutputStream} in a {@link DataOutputStream}
 * and buffers output through a {@link BufferedOutputStream}. */
public class NFSDataOutputStream extends DataOutputStream {
  
  private static class PositionCache extends FilterOutputStream {
    long position;

    public PositionCache(NFSOutputStream out) throws IOException {
      super(out);
      this.position = out.getPos();
    }

    // This is the only write() method called by BufferedOutputStream, so we
    // trap calls to it in order to cache the position.
    public void write(byte b[], int off, int len) throws IOException {
      out.write(b, off, len);
      position += len;                            // update position
    }
      
    public long getPos() throws IOException {
      return position;                            // return cached position
    }
    
  }

  private static class Buffer extends BufferedOutputStream {
    public Buffer(PositionCache out, int bufferSize) throws IOException {
      super(out, bufferSize);
    }

    public long getPos() throws IOException {
      return ((PositionCache)out).getPos() + this.count;
    }

    // optimized version of write(int)
    public void write(int b) throws IOException {
      if (count >= buf.length) {
        super.write(b);
      } else {
        buf[count++] = (byte)b;
      }
    }

  }

  public NFSDataOutputStream(NFSOutputStream out) throws IOException {
    this(out, NutchConf.getInt("io.file.buffer.size", 4096));
  }

  public NFSDataOutputStream(NFSOutputStream out, int bufferSize)
    throws IOException {
    super(new Buffer(new PositionCache(out), bufferSize));
  }

  public long getPos() throws IOException {
    return ((Buffer)out).getPos();
  }

}