alluxio.client.file

Class FileInStream

java.lang.Object

java.io.InputStream

alluxio.client.file.FileInStream

All Implemented Interfaces:

BoundedStream, PositionedReadable, Positioned, Seekable, Closeable, AutoCloseable

@PublicApi
 @NotThreadSafe
public class FileInStream
extends InputStream
implements BoundedStream, PositionedReadable, Seekable

A streaming API to read a file. This API represents a file as a stream of bytes and provides a collection of read() methods to access this stream of bytes. In addition, one can seek into a given offset of the stream to read. This class wraps the block in stream for each of the blocks in the file and abstracts the switching between streams. The backing streams can read from Alluxio space in the local machine, remote machines, or the under storage system. The internal bookkeeping works as follows: 1. updateStream() is a potentially expensive operation and is responsible for creating new BlockInStreams and updating mBlockInStream. After calling this method, mBlockInStream is ready to serve reads from the current mPosition. 2. mPosition can become out of sync with mBlockInStream when seek or skip is called. When this happens, mBlockInStream is set to null and no effort is made to sync between the two until updateStream() is called. 3. updateStream() is only called when followed by a read request. Thus, if a mBlockInStream is created, it is guaranteed we read at least one byte from it.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	FileInStream(URIStatus status, InStreamOptions options, FileSystemContext context)

Method Summary

Modifier and Type	Method and Description
void	close()
long	getPos()
int	positionedRead(long pos, byte[] b, int off, int len) Reads up to the specified number of bytes, from a given position within a file, and return the number of bytes read.
int	read()
int	read(byte[] b)
int	read(byte[] b, int off, int len)
long	remaining()
void	seek(long pos) Moves the starting read position of the stream to the specified position which is relative to the start of the stream.
long	skip(long n)

Methods inherited from class java.io.InputStream

available, mark, markSupported, reset

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

FileInStream

protected FileInStream(URIStatus status,
                       InStreamOptions options,
                       FileSystemContext context)
                throws IOException

Throws:

IOException

Method Detail

read

public int read()
         throws IOException

Specified by:

read in class InputStream

Throws:

IOException

read

public int read(byte[] b)
         throws IOException

Overrides:

read in class InputStream

Throws:

IOException

read

public int read(byte[] b,
                int off,
                int len)
         throws IOException

Overrides:

read in class InputStream

Throws:

IOException

skip

public long skip(long n)
          throws IOException

Overrides:

skip in class InputStream

Throws:

IOException

close

public void close()
           throws IOException

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

Overrides:

close in class InputStream

Throws:

IOException

remaining

public long remaining()

Specified by:

remaining in interface BoundedStream

Returns:

the remaining number of bytes left in the stream, starting at the current position

positionedRead

public int positionedRead(long pos,
                          byte[] b,
                          int off,
                          int len)
                   throws IOException

Description copied from interface: PositionedReadable

Reads up to the specified number of bytes, from a given position within a file, and return the number of bytes read. This does not change the current offset of a file, and is thread-safe. Not all implementations meet the thread safety requirement. According to the documentation of the PositionedReadable interface in Hadoop, those that do not meet the requirement cannot be used as a backing store for some applications, such as Apache HBase. All implementations of this interface in Alluxio must meet the thread safety requirement.

Specified by:

positionedRead in interface PositionedReadable

Parameters:

pos - position within file

b - destination buffer

off - offset in the buffer

len - number of bytes to read

Returns:

actual number of bytes read; -1 means "EOF";

Throws:

IOException

getPos

public long getPos()

Specified by:

getPos in interface Positioned

Returns:

the current position

seek

public void seek(long pos)
          throws IOException

Description copied from interface: Seekable

Moves the starting read position of the stream to the specified position which is relative to the start of the stream. Seeking to a position before the current read position is supported.

Specified by:

seek in interface Seekable

Parameters:

pos - the position to seek to, it must be between 0 and the end of the stream - 1

Throws:

IOException