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package eu.dnetlib.dhp.common.java.io;
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import java.io.IOException;
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import java.util.NoSuchElementException;
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import java.util.regex.Pattern;
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import org.apache.hadoop.fs.FileSystem;
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import org.apache.hadoop.fs.LocatedFileStatus;
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import org.apache.hadoop.fs.RemoteIterator;
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import org.apache.hadoop.io.SequenceFile;
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import org.apache.hadoop.io.SequenceFile.Reader;
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import org.apache.hadoop.io.Text;
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import org.apache.hadoop.io.Writable;
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import org.apache.hadoop.util.ReflectionUtils;
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/**
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* Iterator that extracts sequence file's consecutive {@link Text} values.
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*
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* @author mhorst
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*/
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public class SequenceFileTextValueReader implements CloseableIterator<Text> {
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private SequenceFile.Reader sequenceReader;
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private final RemoteIterator<LocatedFileStatus> fileIt;
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private final FileSystem fs;
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/**
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* Ignore file starting with underscore. Such files are also ignored by
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* default by map-reduce jobs.
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*/
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private final static Pattern WHITELIST_REGEXP = Pattern.compile("^[^_].*");
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private Text toBeReturned;
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//------------------------ CONSTRUCTORS --------------------------
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/**
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* Default constructor.
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*
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* @param path HDFS path along with associated FileSystem
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* @throws IOException
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*/
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public SequenceFileTextValueReader(final FileSystemPath path) throws IOException {
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this.fs = path.getFileSystem();
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if (fs.isDirectory(path.getPath())) {
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fileIt = fs.listFiles(path.getPath(), false);
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sequenceReader = getNextSequenceReader();
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} else {
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fileIt = null;
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sequenceReader = new Reader(fs.getConf(), SequenceFile.Reader.file(path.getPath()));
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}
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}
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//------------------------ LOGIC ---------------------------------
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/*
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* (non-Javadoc)
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*
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* @see java.util.Iterator#hasNext()
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*/
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@Override
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public boolean hasNext() {
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// check and provide next when already returned
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if (toBeReturned == null) {
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toBeReturned = getNext();
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}
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return toBeReturned != null;
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}
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/*
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* (non-Javadoc)
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*
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* @see java.util.Iterator#next()
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*/
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@Override
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public Text next() {
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if (toBeReturned != null) {
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// element fetched while executing hasNext()
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Text result = toBeReturned;
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toBeReturned = null;
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return result;
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} else {
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Text resultCandidate = getNext();
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if (resultCandidate!=null) {
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return resultCandidate;
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} else {
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throw new NoSuchElementException();
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}
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}
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}
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/*
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* (non-Javadoc)
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*
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* @see eu.dnetlib.dhp.exp.iterator.ClosableIterator#close()
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*/
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@Override
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public void close() throws IOException {
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if (sequenceReader != null) {
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sequenceReader.close();
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}
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}
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//------------------------ PRIVATE -------------------------------
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private final Reader getNextSequenceReader() throws IOException {
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while (fileIt != null && fileIt.hasNext()) {
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LocatedFileStatus currentFileStatus = fileIt.next();
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if (isValidFile(currentFileStatus)) {
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return new Reader(this.fs.getConf(), SequenceFile.Reader.file(currentFileStatus.getPath()));
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}
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}
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// fallback
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return null;
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}
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/**
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* Checks whether file is valid candidate.
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*
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* @param fileStatus
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* file status holding file name
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* @return true when valid, false otherwise
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*/
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private final boolean isValidFile(LocatedFileStatus fileStatus) {
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if (fileStatus.isFile()) {
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return WHITELIST_REGEXP.matcher(fileStatus.getPath().getName()).matches();
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} else {
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return false;
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}
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}
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/**
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* @return next data package
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*/
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private Text getNext() {
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try {
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if (sequenceReader == null) {
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return null;
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}
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Writable key = (Writable) ReflectionUtils.newInstance(sequenceReader.getKeyClass(), fs.getConf());
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Writable value = (Writable) ReflectionUtils.newInstance(sequenceReader.getValueClass(), fs.getConf());
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if (sequenceReader.next(key, value)) {
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return (Text) value;
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} else {
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sequenceReader.close();
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sequenceReader = getNextSequenceReader();
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if (sequenceReader != null) {
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return getNext();
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}
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}
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// fallback
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return null;
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} catch (IOException e) {
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throw new RuntimeException(e);
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}
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}
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}
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