org.apache.hadoop.fs
Class FSDataInputStream

java.lang.Object
  extended by java.io.InputStream
      extended by java.io.FilterInputStream
          extended by java.io.DataInputStream
              extended by org.apache.hadoop.fs.FSDataInputStream
All Implemented Interfaces:
Closeable, DataInput, org.apache.hadoop.fs.ByteBufferReadable, CanSetDropBehind, CanSetReadahead, org.apache.hadoop.fs.HasEnhancedByteBufferAccess, org.apache.hadoop.fs.HasFileDescriptor, PositionedReadable, Seekable

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

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.
 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.
 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.
 
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: org.apache.hadoop.fs.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 org.apache.hadoop.fs.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

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 return null on EOF (and only on EOF). Otherwise, we will return a direct 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.


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