org.apache.hadoop.fs

Interface PositionedReadable

All Known Implementing Classes:

FSDataInputStream, FSInputStream, HdfsDataInputStream

@InterfaceAudience.Public
 @InterfaceStability.Evolving
public interface PositionedReadable

Stream that permits positional reading. Implementations are required to implement thread-safe operations; this may be supported by concurrent access to the data, or by using a synchronization mechanism to serialize access. Not all implementations meet this requirement. Those that do not cannot be used as a backing store for some applications, such as Apache HBase. Independent of whether or not they are thread safe, some implementations may make the intermediate state of the system, specifically the position obtained in Seekable.getPos() visible.

Method Summary

Modifier and Type	Method and Description
int	read(long position, byte[] buffer, int offset, int length) Read up to the specified number of bytes, from a given position within a file, and return the number of bytes read.
void	readFully(long position, byte[] buffer) Read number of bytes equal to the length of the buffer, from a given position within a file.
void	readFully(long position, byte[] buffer, int offset, int length) Read the specified number of bytes, from a given position within a file.

Method Detail

read

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

Read 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. Warning: Not all filesystems satisfy the thread-safety requirement.

Parameters:

position - position within file

buffer - destination buffer

offset - offset in the buffer

length - number of bytes to read

Returns:

actual number of bytes read; -1 means "none"

Throws:

IOException - IO problems.

readFully

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

Read the specified number of bytes, from a given position within a file. This does not change the current offset of a file, and is thread-safe. Warning: Not all filesystems satisfy the thread-safety requirement.

Parameters:

position - position within file

buffer - destination buffer

offset - offset in the buffer

length - number of bytes to read

Throws:

IOException - IO problems.

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

readFully

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

Read number of bytes equal to the length of the buffer, from a given position within a file. This does not change the current offset of a file, and is thread-safe. Warning: Not all filesystems satisfy the thread-safety requirement.

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