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, AutoCloseable, ByteBufferPositionedReadable, ByteBufferReadable, CanSetDropBehind, CanSetReadahead, CanUnbuffer, org.apache.hadoop.fs.HasEnhancedByteBufferAccess, org.apache.hadoop.fs.HasFileDescriptor, PositionedReadable, Seekable, StreamCapabilities

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

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

Field Summary

Fields inherited from class java.io.FilterInputStream

in

Fields inherited from interface org.apache.hadoop.fs.StreamCapabilities

DROPBEHIND, HFLUSH, HSYNC, PREADBYTEBUFFER, READAHEAD, READBYTEBUFFER, UNBUFFER

Constructor Summary

Constructors

Constructor and Description
FSDataInputStream(InputStream in)

Method Summary

Methods

Modifier and Type	Method and Description
FileDescriptor	getFileDescriptor()
long	getPos() Get the current position in the input stream.
boolean	hasCapability(String capability) Query the stream for a specific capability.
int	read(ByteBuffer buf) Reads up to buf.remaining() bytes into buf.
ByteBuffer	read(ByteBufferPool bufferPool, int maxLength)
ByteBuffer	read(ByteBufferPool bufferPool, int maxLength, EnumSet<ReadOption> opts) Get a ByteBuffer containing file data.
int	read(long position, byte[] buffer, int offset, int length) Read bytes from the given position in the stream to the given buffer.
int	read(long position, ByteBuffer buf) Reads up to buf.remaining() bytes into buf from a given position in the file and returns the number of bytes read.
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	releaseBuffer(ByteBuffer buffer) Release a ByteBuffer which was created by the enhanced ByteBuffer read function.
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.
String	toString() String value.
void	unbuffer() Reduce the buffering.

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, wait, wait, wait

Constructor Detail

FSDataInputStream

public FSDataInputStream(InputStream in)

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 - IO problems.

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:

IOException - IO problems

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.

readFully

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

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

Specified by:

readFully in interface PositionedReadable

Parameters:

position - position within file

buffer - destination buffer

Throws:

IOException - IO problems.

EOFException - the end of the data was reached before the read operation completed

seekToNewSource

public boolean seekToNewSource(long targetPos)
                        throws IOException

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

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() will be advanced by the number of bytes read and buf.limit() should be unchanged.

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.

Returns:

the number of bytes read, possibly zero, or -1 if reach end-of-stream

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

read

public ByteBuffer read(ByteBufferPool bufferPool,
              int maxLength,
              EnumSet<ReadOption> opts)
                throws IOException,
                       UnsupportedOperationException

Description copied from interface: org.apache.hadoop.fs.HasEnhancedByteBufferAccess

Get a ByteBuffer containing file data. This ByteBuffer may come from the stream itself, via a call like mmap, or it may come from the ByteBufferFactory which is passed in as an argument.

Specified by:

read in interface org.apache.hadoop.fs.HasEnhancedByteBufferAccess

Parameters:

bufferPool - If this is non-null, it will be used to create a fallback ByteBuffer when the stream itself cannot create one.

maxLength - The maximum length of buffer to return. We may return a buffer which is shorter than this.

opts - Options to use when reading.

Returns:

We will always return an empty buffer if maxLength was 0, whether or not we are at EOF. If maxLength > 0, we will return null if the stream has reached EOF. Otherwise, we will return a ByteBuffer containing at least one byte. You must free this ByteBuffer when you are done with it by calling releaseBuffer on it. The buffer will continue to be readable until it is released in this manner. However, the input stream's close method may warn about unclosed buffers.

Throws:

IOException

UnsupportedOperationException

read

public final ByteBuffer read(ByteBufferPool bufferPool,
              int maxLength)
                      throws IOException,
                             UnsupportedOperationException

Throws:

IOException

UnsupportedOperationException

releaseBuffer

public void releaseBuffer(ByteBuffer buffer)

Description copied from interface: org.apache.hadoop.fs.HasEnhancedByteBufferAccess

Release a ByteBuffer which was created by the enhanced ByteBuffer read function. You must not continue using the ByteBuffer after calling this function.

Specified by:

releaseBuffer in interface org.apache.hadoop.fs.HasEnhancedByteBufferAccess

Parameters:

buffer - The ByteBuffer to release.

unbuffer

public void unbuffer()

Description copied from interface: CanUnbuffer

Reduce the buffering. This will also free sockets and file descriptors held by the stream, if possible.

Specified by:

unbuffer in interface CanUnbuffer

hasCapability

public boolean hasCapability(String capability)

Description copied from interface: StreamCapabilities

Query the stream for a specific capability.

Specified by:

hasCapability in interface StreamCapabilities

Parameters:

capability - string to query the stream support for.

Returns:

True if the stream supports capability.

toString

public String toString()

String value. Includes the string value of the inner stream

Overrides:

toString in class Object

Returns:

the stream

read

public int read(long position,
       ByteBuffer buf)
         throws IOException

Description copied from interface: ByteBufferPositionedReadable

Reads up to buf.remaining() bytes into buf from a given position in the file and returns the number of bytes read. Callers should use buf.limit(...) to control the size of the desired read and buf.position(...) to control the offset into the buffer the data should be written to.

After a successful call, buf.position() will be advanced by the number of bytes read and buf.limit() will be unchanged.

In the case of an exception, the state of the buffer (the contents of the buffer, the buf.position(), the buf.limit(), etc.) is undefined, and callers should be prepared to recover from this eventuality.

Callers should use StreamCapabilities.hasCapability(String) with StreamCapabilities.PREADBYTEBUFFER to check if the underlying stream supports this interface, otherwise they might get a UnsupportedOperationException.

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

Specified by:

read in interface ByteBufferPositionedReadable

Parameters:

position - position within file

buf - the ByteBuffer to receive the results of the read operation.

Returns:

the number of bytes read, possibly zero, or -1 if reached end-of-stream

Throws:

IOException - if there is some error performing the read