yacy_search_server/source/net/yacy/kelondro/blob/Gap.java

// Gap.java
// (C) 2008 by Michael Peter Christen; mc@yacy.net, Frankfurt a. M., Germany
// first published 30.12.2008 on http:// yacy.net
// 
// This is a part of YaCy, a peer-to-peer based web search engine
// 
// $LastChangedDate$
// $LastChangedRevision$
// $LastChangedBy$
// 
// LICENSE
// 
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
// 
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
// 
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

package net.yacy.kelondro.blob;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Iterator;
import java.util.Map;
import java.util.TreeMap;

/**
 * this is an extension of a set of {seek, size} pairs
 * it is used to denote the position and space of free records
 * The class provides methods to dump such a set to a file and read it again
 */

public class Gap extends TreeMap<Long, Integer> {
    
    private static final long serialVersionUID = 1L;

    public Gap() {
        super();
    }
    
    /**
     * initialize a kelondroBLOBGap with the content of a dump
     * @param file
     * @throws IOException 
     * @throws IOException 
     */
    public Gap(final File file) throws IOException {
        super();
        // read the index dump and fill the index
        DataInputStream is;
        FileInputStream fis = null;
        try {
        	fis = new FileInputStream(file);
            is = new DataInputStream(new BufferedInputStream(fis, (Integer.SIZE + Long.SIZE) * 1024)); // equals 16*1024*recordsize
        } catch (final OutOfMemoryError e) {
        	if(fis != null) {
        		/* Reuse if possible the already created FileInputStream */
                is = new DataInputStream(fis);
        	} else {
        		is = new DataInputStream(new FileInputStream(file));
        	}

        }
        try {
        	long p;
        	int l;
        	while (true) {
        		try {
        			p = is.readLong();
        			l = is.readInt();
        			this.put(Long.valueOf(p), Integer.valueOf(l));
        		} catch (final IOException e) {
        			break;
        		}
        	}
        } finally {
        	if(is != null) {
        		is.close();
        	}
        }
        is = null;
    }
    
    /**
     * dump the set to a file
     * @param file
     * @return
     * @throws IOException
     */
    public int dump(File file) throws IOException {
        File tmp = new File(file.getParentFile(), file.getName() + ".prt");
        Iterator<Map.Entry<Long, Integer>> i = this.entrySet().iterator();
        DataOutputStream os;
        int c = 0;
        try (/* Resource automatically closed by this try-with-resources statement */
        		final FileOutputStream fileStream = new FileOutputStream(tmp);
        ) {
        	try {
        		os = new DataOutputStream(new BufferedOutputStream(fileStream, (Integer.SIZE + Long.SIZE) * 1024)); // = 16*1024*recordsize
        	} catch (final OutOfMemoryError e) {
        		os = new DataOutputStream(fileStream);
        	}
        	try {
        		Map.Entry<Long, Integer> e;
        		while (i.hasNext()) {
        			e = i.next();
        			os.writeLong(e.getKey().longValue());
        			os.writeInt(e.getValue().intValue());
        			c++;
        		}
        		os.flush();
        	} finally {
        		os.close();
        	}
        }
        tmp.renameTo(file);
        assert file.exists() : file.toString();
        assert !tmp.exists() : tmp.toString();
        
        return c;
    }

}