client

Class DFSInputStream

java.lang.Object

java.io.InputStream

client.DFSInputStream

All Implemented Interfaces:

java.io.Closeable, java.lang.AutoCloseable

public class DFSInputStream
extends java.io.InputStream

Input stream backed by a file in the distributed filesystem.

Read calls on a DFSInputStream are directed to a storage server hosting the given file. Each read call corresponds to one network request. If this behavior is not desirable, the DFSInputStream should be wrapped in a BufferedInputStream or other class providing buffered input.

DFSInputStream does not support marks. DFSInputStream does not provide locking. This must be done manually by the user. The reason for this is that if DFSInputStream attempted to lock a file for shared access, it would not be possible to combine use of the input stream with other operations, such as retrieving file size, or operations that require the parent directory of the file to be locked for exclusive access.

Field Summary

Fields

Modifier and Type	Field and Description
private boolean	closed Indicates that the stream has been closed.
private long	length Total file length.
private Service	naming_server Naming server used to find the storage server hosting the file.
private long	offset Current read offset in the file.
private Path	path Path to the file.
private Storage	storage_server Storage server hosting the file.

Constructor Summary

Constructors

Constructor and Description
DFSInputStream(Service naming_server, Path file) Creates a DFSInputStream for a file listed by the given naming server.
DFSInputStream(Service naming_server, java.lang.String filename) Creates a DFSInputStream for a file listed by the given naming server.
DFSInputStream(java.lang.String hostname, Path file) Creates a DFSInputStream for a file listed by the given naming server.
DFSInputStream(java.lang.String hostname, java.lang.String filename) Creates a DFSInputStream for a file listed by the given naming server.

Method Summary

Modifier and Type	Method and Description
int	available() Returns the number of bytes remaining between the current stream offset and the end of file.
void	close() Closes the input stream.
int	read() Reads a single byte from the input stream.
int	read(byte[] buffer, int buffer_offset, int read_length) Reads bytes from the input stream into a byte buffer.
long	skip(long count) Advances the stream offset.

Methods inherited from class java.io.InputStream

mark, markSupported, read, reset

Methods inherited from class java.lang.Object

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

Field Detail

path

private final Path path

Path to the file.

storage_server

private final Storage storage_server

Storage server hosting the file.

naming_server

private final Service naming_server

Naming server used to find the storage server hosting the file.

offset

private long offset

Current read offset in the file.

length

private final long length

Total file length.

closed

private boolean closed

Indicates that the stream has been closed.

Constructor Detail

DFSInputStream

public DFSInputStream(Service naming_server,
                      Path file)
               throws java.io.FileNotFoundException,
                      java.io.IOException

Creates a DFSInputStream for a file listed by the given naming server.

The file should be locked on the naming server for shared access.

Parameters:

naming_server - Stub for the naming server hosting metadata for the file.

file - Path to the file.

Throws:

java.io.FileNotFoundException - If the file is not listed by the given naming server, or if the path refers to a directory.

java.io.IOException - If either the naming server or the storage server hosting the file cannot be contacted to retrieve file metadata.

DFSInputStream

public DFSInputStream(java.lang.String hostname,
                      Path file)
               throws java.io.FileNotFoundException,
                      java.io.IOException

Creates a DFSInputStream for a file listed by the given naming server.

The file should be locked on the naming server for shared access. The naming server is contacted on the default client interface port.

Parameters:

hostname - Address of the naming server hosting metadata for the file.

file - Path to the file.

Throws:

java.io.FileNotFoundException - If the file is not listed by the given naming server, or if the path refers to a directory.

java.io.IOException - If either the naming server or the storage server hosting the file cannot be contacted to retrieve file metadata.

DFSInputStream

public DFSInputStream(Service naming_server,
                      java.lang.String filename)
               throws java.io.FileNotFoundException,
                      java.io.IOException

Creates a DFSInputStream for a file listed by the given naming server.

The file should be locked on the naming server for shared access.

Parameters:

naming_server - Stub for the naming server hosting metadata for the file.

filename - Path to the file, as a string.

Throws:

java.io.FileNotFoundException - If the file is not listed by the given naming server, or if the path refers to a directory.

java.io.IOException - If either the naming server or the storage server hosting the file cannot be contacted to retrieve file metadata.

DFSInputStream

public DFSInputStream(java.lang.String hostname,
                      java.lang.String filename)
               throws java.io.FileNotFoundException,
                      java.io.IOException

Creates a DFSInputStream for a file listed by the given naming server.

The file should be locked on the naming server for shared access. The naming server is contacted on the default client interface port.

Parameters:

hostname - Address of the naming server hosting metadata for the file.

filename - Path to the file, as a string.

Throws:

java.io.FileNotFoundException - If the file is not listed by the given naming server, or if the path refers to a directory.

java.io.IOException - If either the naming server or the storage server hosting the file cannot be contacted to retrieve file metadata.

Method Detail

close

public void close()

Closes the input stream.

The stream is marked as closed. Further attempts to use the input stream will result in IOException.

Specified by:

close in interface java.io.Closeable

Specified by:

close in interface java.lang.AutoCloseable

Overrides:

close in class java.io.InputStream

read

public int read(byte[] buffer,
                int buffer_offset,
                int read_length)
         throws java.io.IOException

Reads bytes from the input stream into a byte buffer.

The read is performed in a single request to the storage server. If the operation succeeds, the number of bytes read will be either read_length or the number of bytes remaining in the file, whichever is less.

Overrides:

read in class java.io.InputStream

Parameters:

buffer - Buffer to receive bytes read from the stream.

buffer_offset - Offset into the buffer at which the bytes are to be written.

read_length - The maximum number of bytes to read.

Returns:

The number of bytes successfully read, or -1 if the end of file is reached before any bytes are read. The number of bytes successfully read may be zero if read_length is zero.

Throws:

java.io.IOException - If the stream is closed, if the storage server cannot be contacted, or if a read error occurs on the storage server.

java.lang.NullPointerException - If buffer is null.

java.lang.IndexOutOfBoundsException - If buffer_offset or read_length is negative, or if buffer_offset + read_length exceeds the length of the given buffer.

read

public int read()
         throws java.io.IOException

Reads a single byte from the input stream.

Specified by:

read in class java.io.InputStream

Returns:

The value of the byte read, as an integer between 0 and 255, or -1 if the end of file has been reached.

Throws:

java.io.IOException - If the stream is closed, if the storage server cannot be contacted, or if a read error occurs on the storage server.

skip

public long skip(long count)
          throws java.io.IOException

Advances the stream offset.

The stream offset is advanced by either the given number of bytes, or by the number of bytes remaining in the file, whichever is less.

Overrides:

skip in class java.io.InputStream

Parameters:

count - Number of bytes by which the stream offset should be advanced.

Returns:

The number of bytes by which the stream offset has actually been advanced. This number may be zero.

Throws:

java.io.IOException - If the stream has been closed.

available

public int available()
              throws java.io.IOException

Returns the number of bytes remaining between the current stream offset and the end of file.

The number returned is exact and not an estimate. However, if the number exceeds Integer.MAX_VALUE, it is clamped to Integer.MAX_VALUE.

Overrides:

available in class java.io.InputStream

Throws:

java.io.IOException - If the stream has been closed.