/*
* Terrier - Terabyte Retriever
* Webpage: http://terrier.org
* Contact: terrier{a.}dcs.gla.ac.uk
* University of Glasgow - School of Computing Science
* http://www.gla.ac.uk/
*
* The contents of this file are subject to the Mozilla Public License
* Version 1.1 (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.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS"
* basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
* the License for the specific language governing rights and limitations
* under the License.
*
* The Original Code is RunWriter.java.
*
* The Original Code is Copyright (C) 2004-2011 the University of Glasgow.
* All Rights Reserved.
*
* Contributor(s):
* Roi Blanco (rblanc{at}@udc.es)
* Craig Macdonald (craigm{at}dcs.gla.ac.uk)
*/
package org.terrier.structures.indexing.singlepass;
import java.io.DataOutputStream;
import java.io.IOException;
import org.terrier.compression.BitOutputStream;
import org.terrier.compression.MemorySBOS;
import org.terrier.utility.Files;
/**
* This class writes a run to disk. The data written depends on the specific subclass.
* This one, writes the Nt, TF and the <docid, tf> sequence.
* It also writes the max frequency of a term in the run (useful for allocating memory during the merging phase).
* @author Roi Blanco
*/
public class RunWriter {
/** Underlying {@link org.terrier.compression.BitOutputStream} to write the compressed objects */
protected final BitOutputStream bos;
/** Underlying {@link java.io.DataOutputStream} to write the term Strings */
protected final DataOutputStream stringDos;
/** Debug String representation of this RunWriter */
protected String info;
protected RunWriter()
{
bos = null;
stringDos = null;
info = null;
}
/** other constructor for use by subclasses */
protected RunWriter(BitOutputStream _bos, DataOutputStream _stringDos) throws IOException
{
this.bos = _bos;
this.stringDos = _stringDos;
this.info = "RunWriter(Streams)";
}
/**
* Instanciates a RunWriter, given the filenames to write.
* @param fileName name of the file to write the posting lists data.
* @param termsFile name of the file to write the terms.
* @throws IOException if an I/O error occurs.
*/
public RunWriter(String fileName, String termsFile) throws IOException{
bos = new BitOutputStream(fileName);
stringDos = new DataOutputStream( Files.writeFileStream(termsFile));
this.info = "RunWriter("+fileName+")";
}
/** Returns true if this RunWriter needs writeTerm() to be called sorted by term */
public boolean writeSorted()
{
return true;
}
/**
* Writes the headers of the run.
* @param maxSize max size of a posting.
* @param size number of postings in the run.
* @throws IOException if an I/O error occurs.
*/
public void beginWrite(int maxSize, int size) throws IOException{
bos.writeGamma(maxSize);
bos.writeGamma(size);
}
/**
* Writes the information for a given term.
* @param term the term to write.
* @param post the Posting with the data of the term.
* @throws IOException if an I/O error occurs.
*/
public void writeTerm(final String term, final Posting post) throws IOException{
stringDos.writeUTF(term);
bos.writeGamma(post.getDocF());
bos.writeGamma(post.getTF());
//System.err.println("Writing "+term + " TF="+post.getTF()+ " Nt="+post.getDocF());
final MemorySBOS Docs = post.getDocs();
Docs.pad();
/* when reading, ie RunReader and it's children classes
* an align call is required here. */
bos.append(Docs.getMOS().getBuffer(), Docs.getMOS().getPos());
}
/**
* Closes the output streams.
* @throws IOException if an I/O error occurs.
*/
public void finishWrite() throws IOException{
bos.close();
stringDos.close();
}
/**
* {@inheritDoc}
*/
public String toString()
{
return info;
}
}