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// ChunkIterator.java
// (C) 2008 by Michael Peter Christen; mc@yacy.net, Frankfurt a. M., Germany
// first published 14.01.2008 on http://yacy.net
//
// $LastChangedDate$
// $LastChangedRevision$
// $LastChangedBy$
//
// 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.table;
import java.io.BufferedInputStream;
import java.io.DataInputStream;
import java.io.EOFException;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.Iterator;
import net.yacy.cora.util.ConcurrentLog;
import net.yacy.cora.util.LookAheadIterator;
public class ChunkIterator extends LookAheadIterator<byte[]> implements Iterator<byte[]> {
private final int chunksize;
/**
* create a ChunkIterator
* a ChunkIterator uses a BufferedInputStream to iterate through the file
* and is therefore a fast option to get all elements in the file as a sequence
* ATTENTION: before calling this class ensure that all file buffers are flushed
* ATTENTION: if the iterator is not read to the end or interrupted, close() must be called to release the InputStream
* @param file: the file
* @param recordsize: the size of the elements in the file
* @param chunksize: the size of the chunks that are returned by next(). remaining bytes until the length of recordsize are skipped
* @throws FileNotFoundException
*/
private final DataInputStream stream;
private final int recordsize;
public ChunkIterator(final File file, final int recordsize, final int chunksize) throws FileNotFoundException {
if (!file.exists()) throw new FileNotFoundException(file.getAbsolutePath());
assert (file.exists());
assert file.length() % recordsize == 0;
this.recordsize = recordsize;
this.chunksize = chunksize;
this.stream = new DataInputStream(new BufferedInputStream(new FileInputStream(file), 64 * 1024));
}
/**
* Special close method to release the used InputStream
* stream is automatically closed on last next(),
* close() needs only to be called if iterator did not read to the end ( hasNext() or next() has not returned null)
* @throws IOException when the stream could not be closed
*/
public void close() throws IOException {
this.stream.close();
}
@Override
public byte[] next0() {
final byte[] chunk = new byte[chunksize];
int r, s;
byte[] result = null;
try {
// read the chunk
this.stream.readFully(chunk);
// skip remaining bytes
r = chunksize;
boolean skipError = false;
while (r < recordsize) {
s = (int) this.stream.skip(recordsize - r);
assert s > 0;
if (s <= 0) {
skipError = true;
break;
}
r += s;
}
if(!skipError) {
result = chunk;
}
} catch (final EOFException e) {
// no real exception, this is the normal termination
result = null;
} catch (final IOException e) {
/* Return normally but trace the exception in log */
ConcurrentLog.logException(e);
result = null;
} finally {
if(result == null) {
/* when result is null (normal termination or not),
* we must ensure the underlying input stream is closed as we must not keep system file handlers open */
try {
this.stream.close();
} catch (IOException ex) {
ConcurrentLog.logException(ex);
}
}
}
return result;
}
}
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