org.apache.hadoop.fs
Class FSDataInputStream

java.lang.Object
  java.io.InputStream
      java.io.FilterInputStream
          java.io.DataInputStream
              org.apache.hadoop.fs.FSDataInputStream

All Implemented Interfaces:

Closeable, DataInput, ByteBufferReadable, CanSetDropBehind, CanSetReadahead, org.apache.hadoop.fs.HasFileDescriptor, PositionedReadable, Seekable

@InterfaceAudience.Public
@InterfaceStability.Stable
public class FSDataInputStream
extends DataInputStream
implements Seekable, PositionedReadable, Closeable, ByteBufferReadable, org.apache.hadoop.fs.HasFileDescriptor, CanSetDropBehind, CanSetReadahead

Utility that wraps a FSInputStream in a DataInputStream and buffers input through a BufferedInputStream.

Field Summary

Fields inherited from class java.io.FilterInputStream

in

Constructor Summary

FSDataInputStream(InputStream in)

Method Summary

FileDescriptor	getFileDescriptor()
long	getPos() Get the current position in the input stream.
int	read(ByteBuffer buf) Reads up to buf.remaining() bytes into buf.
int	read(long position, byte[] buffer, int offset, int length) Read bytes from the given position in the stream to the given buffer.
void	readFully(long position, byte[] buffer) See readFully(long, byte[], int, int).
void	readFully(long position, byte[] buffer, int offset, int length) Read bytes from the given position in the stream to the given buffer.
void	seek(long desired) Seek to the given offset.
boolean	seekToNewSource(long targetPos) Seek to the given position on an alternate copy of the data.
void	setDropBehind(Boolean dropBehind) Configure whether the stream should drop the cache.
void	setReadahead(Long readahead) Set the readahead on this stream.

Methods inherited from class java.io.DataInputStream

read, read, readBoolean, readByte, readChar, readDouble, readFloat, readFully, readFully, readInt, readLine, readLong, readShort, readUnsignedByte, readUnsignedShort, readUTF, readUTF, skipBytes

Methods inherited from class java.io.FilterInputStream

available, close, mark, markSupported, read, reset, skip

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.io.Closeable

close

Constructor Detail

FSDataInputStream

public FSDataInputStream(InputStream in)
                  throws IOException

Throws:

IOException

Method Detail

seek

public void seek(long desired)
          throws IOException

Seek to the given offset.

Specified by:

seek in interface Seekable

Parameters:

desired - offset to seek to

Throws:

IOException

getPos

public long getPos()
            throws IOException

Get the current position in the input stream.

Specified by:

getPos in interface Seekable

Returns:

current position in the input stream

Throws:

IOException

read

public int read(long position,
                byte[] buffer,
                int offset,
                int length)
         throws IOException

Read bytes from the given position in the stream to the given buffer.

Specified by:

read in interface PositionedReadable

Parameters:

position - position in the input stream to seek

buffer - buffer into which data is read

offset - offset into the buffer in which data is written

length - maximum number of bytes to read

Returns:

total number of bytes read into the buffer, or -1 if there is no more data because the end of the stream has been reached

Throws:

IOException

readFully

public void readFully(long position,
                      byte[] buffer,
                      int offset,
                      int length)
               throws IOException

Read bytes from the given position in the stream to the given buffer. Continues to read until length bytes have been read.

Specified by:

readFully in interface PositionedReadable

Parameters:

position - position in the input stream to seek

buffer - buffer into which data is read

offset - offset into the buffer in which data is written

length - the number of bytes to read

Throws:

EOFException - If the end of stream is reached while reading. If an exception is thrown an undetermined number of bytes in the buffer may have been written.

IOException

readFully

public void readFully(long position,
                      byte[] buffer)
               throws IOException

See readFully(long, byte[], int, int).

Specified by:

readFully in interface PositionedReadable

Throws:

IOException

seekToNewSource

public boolean seekToNewSource(long targetPos)
                        throws IOException

Seek to the given position on an alternate copy of the data.

Specified by:

seekToNewSource in interface Seekable

Parameters:

targetPos - position to seek to

Returns:

true if a new source is found, false otherwise

Throws:

IOException

read

public int read(ByteBuffer buf)
         throws IOException

Description copied from interface: ByteBufferReadable

Reads up to buf.remaining() bytes into buf. Callers should use buf.limit(..) to control the size of the desired read.

After a successful call, buf.position() and buf.limit() should be unchanged, and therefore any data can be immediately read from buf. buf.mark() may be cleared or updated.

In the case of an exception, the values of buf.position() and buf.limit() are undefined, and callers should be prepared to recover from this eventuality.

Many implementations will throw UnsupportedOperationException, so callers that are not confident in support for this method from the underlying filesystem should be prepared to handle that exception.

Implementations should treat 0-length requests as legitimate, and must not signal an error upon their receipt.

Specified by:

read in interface ByteBufferReadable

Parameters:

buf - the ByteBuffer to receive the results of the read operation. Up to buf.limit() - buf.position() bytes may be read.

Returns:

the number of bytes available to read from buf

Throws:

IOException - if there is some error performing the read

getFileDescriptor

public FileDescriptor getFileDescriptor()
                                 throws IOException

Specified by:

getFileDescriptor in interface org.apache.hadoop.fs.HasFileDescriptor

Returns:

the FileDescriptor

Throws:

IOException

setReadahead

public void setReadahead(Long readahead)
                  throws IOException,
                         UnsupportedOperationException

Description copied from interface: CanSetReadahead

Set the readahead on this stream.

Specified by:

setReadahead in interface CanSetReadahead

Parameters:

readahead - The readahead to use. null means to use the default.

Throws:

IOException - If there was an error changing the dropBehind setting. UnsupportedOperationException If this stream doesn't support setting readahead.

UnsupportedOperationException

setDropBehind

public void setDropBehind(Boolean dropBehind)
                   throws IOException,
                          UnsupportedOperationException

Description copied from interface: CanSetDropBehind

Configure whether the stream should drop the cache.

Specified by:

setDropBehind in interface CanSetDropBehind

Parameters:

dropBehind - Whether to drop the cache. null means to use the default value.

Throws:

IOException - If there was an error changing the dropBehind setting. UnsupportedOperationException If this stream doesn't support setting the drop-behind.

UnsupportedOperationException