edu.sdsc.grid.io
Class GeneralFileInputStream

java.lang.Object
  java.io.InputStream
      edu.sdsc.grid.io.GeneralFileInputStream

All Implemented Interfaces:

java.io.Closeable

Direct Known Subclasses:

LocalFileInputStream, RemoteFileInputStream

public abstract class GeneralFileInputStream
extends java.io.InputStream

A GeneralFileInputStream obtains input bytes from a file in a file system. What files are available depends on the host environment.

GeneralFileInputStream is meant for reading streams of raw bytes such as image data.

The original intention for this class was to subclass java.io.FileInputStream. But that is not currently the case.

Since:

JARGON1.4

Field Summary

protected int

fd Holds the file descriptor information used by this stream.

Constructor Summary

GeneralFileInputStream(GeneralFile file)
Creates a FileInputStream by opening a connection to an actual file, the file named by the File object file in the file system.

GeneralFileInputStream(GeneralFileSystem fileSystem, java.lang.String name)
Creates a FileInputStream by opening a connection to an actual file, the file named by the path name name in the file system.

Method Summary

abstract int	available() Returns the number of bytes that can be read (or skipped over) from this input stream without blocking by the next caller of a method for this input stream.
abstract void	close() Closes this input stream and releases any system resources associated with the stream.
protected void	finalize() Ensures that the close method of this file input stream is called when there are no more references to it.
protected abstract void	open(GeneralFile file) Opens the given file for use by this stream.
abstract int	read() Reads the next byte of data from the input stream.
int	read(byte[] b) Reads some number of bytes from the input stream and stores them into the buffer array b.
abstract int	read(byte[] b, int off, int len) Reads up to len bytes of data from the input stream into an array of bytes.
abstract long	skip(long n) Skips over and discards n bytes of data from this input stream.

Methods inherited from class java.io.InputStream

mark, markSupported, reset

Methods inherited from class java.lang.Object

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

Field Detail

fd

protected int fd

Holds the file descriptor information used by this stream.

Constructor Detail

GeneralFileInputStream

public GeneralFileInputStream(GeneralFileSystem fileSystem,
                              java.lang.String name)
                       throws java.io.IOException

Creates a FileInputStream by opening a connection to an actual file, the file named by the path name name in the file system.

First, the security is checked to verify the file can be read.

If the named file does not exist, is a directory rather than a regular file, or for some other reason cannot be opened for reading then a IOException is thrown.

Parameters:

name - the system-dependent file name.

Throws:

java.io.IOException - if the file does not exist, is a directory rather than a regular file, or for some other reason cannot be opened for reading.

GeneralFileInputStream

public GeneralFileInputStream(GeneralFile file)
                       throws java.io.IOException

Creates a FileInputStream by opening a connection to an actual file, the file named by the File object file in the file system. A new FileDescriptor object is created to represent this file connection.

First, the security is checked to verify the file can be read.

If the named file does not exist, is a directory rather than a regular file, or for some other reason cannot be opened for reading then a IOException is thrown.

Parameters:

file - the file to be opened for reading.

Throws:

java.io.IOException - if the file does not exist, is a directory rather than a regular file, or for some other reason cannot be opened for reading.

See Also:

File.getPath()

Method Detail

finalize

protected void finalize()
                 throws java.io.IOException

Ensures that the close method of this file input stream is called when there are no more references to it.

Overrides:

finalize in class java.lang.Object

Throws:

java.io.IOException - if an I/O error occurs.

See Also:

close()

open

protected abstract void open(GeneralFile file)
                      throws java.io.IOException

Opens the given file for use by this stream.

Parameters:

file - the file to be opened.

Throws:

java.io.IOException - if an I/O error occurs.

read

public abstract int read()
                  throws java.io.IOException

Reads the next byte of data from the input stream. The value byte is returned as an int in the range 0 to 255. If no byte is available because the end of the stream has been reached, the value -1 is returned. This method blocks until input data is available, the end of the stream is detected, or an exception is thrown.

A subclass must provide an implementation of this method.

Specified by:

read in class java.io.InputStream

Returns:

the next byte of data, or -1 if the end of the stream is reached.

Throws:

java.io.IOException - if an I/O error occurs.

read

public int read(byte[] b)
         throws java.io.IOException

Reads some number of bytes from the input stream and stores them into the buffer array b. The number of bytes actually read is returned as an integer. This method blocks until input data is available, end of file is detected, or an exception is thrown.

If b is null, a NullPointerException is thrown. If the length of b is zero, then no bytes are read and 0 is returned; otherwise, there is an attempt to read at least one byte. If no byte is available because the stream is at end of file, the value -1 is returned; otherwise, at least one byte is read and stored into b.

The first byte read is stored into element b[0], the next one into b[1], and so on. The number of bytes read is, at most, equal to the length of b. Let k be the number of bytes actually read; these bytes will be stored in elements b[0] through b[k-1], leaving elements b[k] through b[b.length-1] unaffected.

If the first byte cannot be read for any reason other than end of file, then an IOException is thrown. In particular, an IOException is thrown if the input stream has been closed.

The read(b) method for class InputStream has the same effect as:

 read(b, 0, b.length) 

Overrides:

read in class java.io.InputStream

Parameters:

b - the buffer into which the data is read.

Returns:

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

Throws:

java.io.IOException - if an I/O error occurs.

java.lang.NullPointerException - if b is null.

See Also:

InputStream.read(byte[], int, int)

read

public abstract int read(byte[] b,
                         int off,
                         int len)
                  throws java.io.IOException

Reads up to len bytes of data from the input stream into an array of bytes. An attempt is made to read as many as len bytes, but a smaller number may be read, possibly zero. The number of bytes actually read is returned as an integer.

This method blocks until input data is available, end of file is detected, or an exception is thrown.

If b is null, a NullPointerException is thrown.

If off is negative, or len is negative, or off+len is greater than the length of the array b, then an IndexOutOfBoundsException is thrown.

If len is zero, then no bytes are read and 0 is returned; otherwise, there is an attempt to read at least one byte. If no byte is available because the stream is at end of file, the value -1 is returned; otherwise, at least one byte is read and stored into b.

The first byte read is stored into element b[off], the next one into b[off+1], and so on. The number of bytes read is, at most, equal to len. Let k be the number of bytes actually read; these bytes will be stored in elements b[off] through b[off+k-1], leaving elements b[off+k] through b[off+len-1] unaffected.

In every case, elements b[0] through b[off] and elements b[off+len] through b[b.length-1] are unaffected.

If the first byte cannot be read for any reason other than end of file, then an IOException is thrown. In particular, an IOException is thrown if the input stream has been closed.

The read(b, off, len) method for class InputStream simply calls the method read() repeatedly. If the first such call results in an IOException, that exception is returned from the call to the read(b, off, len) method. If any subsequent call to read() results in a IOException, the exception is caught and treated as if it were end of file; the bytes read up to that point are stored into b and the number of bytes read before the exception occurred is returned. Subclasses are encouraged to provide a more efficient implementation of this method.

Overrides:

read in class java.io.InputStream

Parameters:

b - the buffer into which the data is read.

off - the start offset in array b at which the data is written.

len - the maximum number of bytes to read.

Returns:

the 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:

java.io.IOException - if an I/O error occurs.

java.lang.NullPointerException - if b is null.

See Also:

InputStream.read()

skip

public abstract long skip(long n)
                   throws java.io.IOException

Skips over and discards n bytes of data from this input stream. The skip method may, for a variety of reasons, end up skipping over some smaller number of bytes, possibly 0. This may result from any of a number of conditions; reaching end of file before n bytes have been skipped is only one possibility. The actual number of bytes skipped is returned. If n is negative, no bytes are skipped.

The skip method of InputStream creates a byte array and then repeatedly reads into it until n bytes have been read or the end of the stream has been reached. Subclasses are encouraged to provide a more efficient implementation of this method.

Overrides:

skip in class java.io.InputStream

Parameters:

n - the number of bytes to be skipped.

Returns:

the actual number of bytes skipped.

Throws:

java.io.IOException - if an I/O error occurs.

available

public abstract int available()
                       throws java.io.IOException

Returns the number of bytes that can be read (or skipped over) from this input stream without blocking by the next caller of a method for this input stream. The next caller might be the same thread or or another thread.

The available method for class InputStream always returns 0.

This method should be overridden by subclasses.

Overrides:

available in class java.io.InputStream

Returns:

the number of bytes that can be read from this input stream without blocking.

Throws:

java.io.IOException - if an I/O error occurs.

close

public abstract void close()
                    throws java.io.IOException

Closes this input stream and releases any system resources associated with the stream.

The close method of InputStream does nothing.

Specified by:

close in interface java.io.Closeable

Overrides:

close in class java.io.InputStream

Throws:

java.io.IOException - if an I/O error occurs.