How to use

FSEditLogOp$Reader

in

org.apache.hadoop.hdfs.server.namenode

 return nextOpImpl(skipBrokenEdits);
case OPEN:
 op = reader.readOp(skipBrokenEdits);
 if ((op != null) && (op.hasTransactionId())) {
  long txId = op.getTransactionId();

 reader = FSEditLogOp.Reader.create(dataIn, tracker, logVersion);
 reader.setMaxOpSize(maxOpSize);
 state = State.OPEN;
} finally {

while (true) {
 try {
  return decodeOp();
 } catch (IOException e) {
  in.reset();

@Override
protected long scanNextOp() throws IOException {
 Preconditions.checkState(state == State.OPEN);
 FSEditLogOp cachedNext = getCachedOp();
 return cachedNext == null ? reader.scanOp() : cachedNext.txid;
}

@Override
protected long scanNextOp() throws IOException {
 Preconditions.checkState(state == State.OPEN);
 FSEditLogOp cachedNext = getCachedOp();
 return cachedNext == null ? reader.scanOp() : cachedNext.txid;
}

void setBytes(byte[] newBytes, int version) throws IOException {
 inner.setData(newBytes);
 tracker = new FSEditLogLoader.PositionTrackingInputStream(inner);
 in = new DataInputStream(tracker);
 this.version = version;
 reader = new FSEditLogOp.Reader(in, tracker, version);
}

@Override
public void setMaxOpSize(int maxOpSize) {
 reader.setMaxOpSize(maxOpSize);
}

@Override
public void setMaxOpSize(int maxOpSize) {
 this.maxOpSize = maxOpSize;
 if (reader != null) {
  reader.setMaxOpSize(maxOpSize);
 }
}

@Override
protected FSEditLogOp nextValidOp() {
 try {
  return reader.readOp(true);
 } catch (IOException e) {
  throw new RuntimeException("got unexpected IOException " + e, e);
 }
}

@Override
protected long scanNextOp() throws IOException {
 Preconditions.checkState(state == State.OPEN);
 FSEditLogOp cachedNext = getCachedOp();
 return cachedNext == null ? reader.scanOp() : cachedNext.txid;
}

@Override
protected FSEditLogOp nextOp() throws IOException {
 Preconditions.checkState(reader != null,
   "Must call setBytes() before readOp()");
 return reader.readOp(false);
}

@Override
public void setMaxOpSize(int maxOpSize) {
 reader.setMaxOpSize(maxOpSize);
}

@Override
protected FSEditLogOp nextOp() throws IOException {
 return reader.readOp(false);
}

@Override
public void setMaxOpSize(int maxOpSize) {
 reader.setMaxOpSize(maxOpSize);
}

@Override
protected FSEditLogOp nextOp() throws IOException {
 Preconditions.checkState(reader != null,
   "Must call setBytes() before readOp()");
 return reader.readOp(false);
}

@Override
public FSEditLogOp readOp() throws IOException {
 return reader.readOp();
}

@Override
public void refresh(long position) throws IOException {
 fc.position(position);
 BufferedInputStream bin = new BufferedInputStream(fStream);
 tracker = new FSEditLogLoader.PositionTrackingInputStream(bin, position);    
 DataInputStream in = new DataInputStream(tracker); 
 reader = new FSEditLogOp.Reader(in, logVersion);
}

/**
 * Open an EditLogInputStream for the given file.
 * @param name filename to open
 * @param firstTxId first transaction found in file
 * @param lastTxId last transaction id found in file
 * @throws LogHeaderCorruptException if the header is either missing or
 *         appears to be corrupt/truncated
 * @throws IOException if an actual IO error occurs while reading the
 *         header
 */
EditLogFileInputStream(File name, long firstTxId, long lastTxId)
  throws LogHeaderCorruptException, IOException {
 file = name;
 rp = new RandomAccessFile(file, "r");    
 fStream = new FileInputStream(rp.getFD());
 fc = rp.getChannel();
 BufferedInputStream bin = new BufferedInputStream(fStream);  
 tracker = new FSEditLogLoader.PositionTrackingInputStream(bin);  
 DataInputStream in = new DataInputStream(tracker);
 try {
  logVersion = readLogVersion(in);
 } catch (EOFException eofe) {
  throw new LogHeaderCorruptException("No header found in log");
 }
 reader = new FSEditLogOp.Reader(in, logVersion);
 this.firstTxId = firstTxId;
 this.lastTxId = lastTxId;
}

@Override
public void setMaxOpSize(int maxOpSize) {
 this.maxOpSize = maxOpSize;
 if (reader != null) {
  reader.setMaxOpSize(maxOpSize);
 }
}

 verifyTerminator();
 return HdfsConstants.INVALID_TXID;
FSEditLogOp op = decodeOp();
return op == null ? HdfsConstants.INVALID_TXID : op.getTransactionId();