java.io
Class FileInputStream

java.lang.Object
  java.io.InputStream
      java.io.FileInputStream

All Implemented Interfaces:

Closeable

public class FileInputStream
extends InputStream

This class is a stream that reads its bytes from a file.

Constructor Summary

FileInputStream(File file)
This method initializes a FileInputStream to read from the specified File object.

FileInputStream(FileDescriptor fdObj)
This method initializes a FileInputStream to read from the specified FileDescriptor object.

FileInputStream(String name)
This method initializes a FileInputStream to read from the specified named file.

Method Summary

int	available() This method returns the number of bytes that can be read from this stream before a read can block.
void	close() This method closes the stream.
protected void	finalize() finalize may be called by the memory management of the virtual machine when it determined that this instance's memory is unreachable and can be reclaimed.
FileChannel	getChannel() This method creates a java.nio.channels.FileChannel.
FileDescriptor	getFD() This method returns a FileDescriptor object representing the underlying native file handle of the file this stream is reading from
int	read() This method reads an unsigned byte from the input stream and returns it as an int in the range of 0-255.
int	read(byte[] buf) This method reads bytes from a stream and stores them into a caller supplied buffer.
int	read(byte[] buf, int offset, int len) This method read bytes from a stream and stores them into a caller supplied buffer.
long	skip(long numBytes) This method skips the specified number of bytes in the 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

Constructor Detail

FileInputStream

public FileInputStream(String name)
                throws FileNotFoundException

This method initializes a FileInputStream to read from the specified named file. A security check is first made to determine whether or not access to this file is allowed. This is done by calling the checkRead() method of the SecurityManager (if one exists) with the name of this file. An exception is thrown if reading is not allowed. If the file does not exist, an exception is also thrown.

Parameters:

name - The name of the file this stream should read from

Throws:

SecurityException - If read access to the file is not allowed

FileNotFoundException - If the file does not exist or if it is a directory

FileInputStream

public FileInputStream(File file)
                throws FileNotFoundException

This method initializes a FileInputStream to read from the specified File object. A security check is first made to determine whether or not access to this file is allowed. This is done by calling the checkRead() method of the SecurityManager (if one exists) with the name of this file. An exception is thrown if reading is not allowed. If the file does not exist, an exception is also thrown.

Parameters:

file - The File object this stream should read from

Throws:

SecurityException - If read access to the file is not allowed

FileNotFoundException - If the file does not exist or if it is a directory.

FileInputStream

public FileInputStream(FileDescriptor fdObj)

This method initializes a FileInputStream to read from the specified FileDescriptor object. A security check is first made to determine whether or not access to this file is allowed. This is done by calling the checkRead() method of the SecurityManager (if one exists) with the specified FileDescriptor An exception is thrown if reading is not allowed.

Parameters:

fdObj - The FileDescriptor object this stream should read from

Throws:

SecurityException - If read access to the file is not allowed

Method Detail

available

public int available()
              throws IOException

This method returns the number of bytes that can be read from this stream before a read can block. A return of 0 indicates that blocking might (or might not) occur on the very next read attempt.

This method returns the number of unread bytes remaining in the file if the descriptor being read from is an actual file. If this method is reading from a ''special'' file such a the standard input, this method will return the appropriate value for the stream being read.

Be aware that reads on plain files that do not reside locally might possibly block even if this method says they should not. For example, a remote server might crash, preventing an NFS mounted file from being read.

Overrides:

available in class InputStream

Returns:

The number of bytes that can be read before blocking could occur

Throws:

IOException - If an error occurs

close

public void close()
           throws IOException

This method closes the stream. Any futher attempts to read from the stream will likely generate an IOException since the underlying file will be closed.

Specified by:

close in interface Closeable

Overrides:

close in class InputStream

Throws:

IOException - If an error occurs.

finalize

protected void finalize()
                 throws IOException

Description copied from class: Object

finalize may be called by the memory management of the virtual machine when it determined that this instance's memory is unreachable and can be reclaimed.

NOTE: The use of finalize() is strongly discouraged for realtime or safety-critical code. This method should only be used for debugging purposes. If used as a last resort to reclaim non-memory resouces, finalize() should indicate the resource leak with a loud error message.

There is no guarantee that finalize() will be called, the memory management may decide not to reclaim this object's memory or to delay the call to finalize() to an unspecified point in time. It is therefore recommended never to use the finalize method to release any resources (files, network connections, non-Java memory, etc.) since releasing of these resource may be delayed perpetually.

The order of finalization is not specified, i.e., the finalize method of any two objects that become unreachable may be called in an arbitrary order. It therefore has to be assumed that when finalize() is called on an object, that the finalize() method of any object that is only reachable through this object() has been called as well or is called simultaneously by another thread.

The presence of a finalize-method in any sub-class of Object causes the reclamation of the memory of this object to be delayed until the finalize() method has been executed. The finalize() method is typically executed by the finalizer thread (that may run at a low priority) or by a call to Runtime.runFinalization().

Any code sequence that creates instances of a class that defines a finalize() method must therefore ensure that sufficient CPU time is allocated to the finalizer thread or that Runtime.runFinalization() is called regularly such that the finalize() methods can be executed and the object's memory can be reclaimed.

The finalize method itself should never block or run for long times since it would otherwise block the finalizer thread or the thread that called Runtime.runFinalization() and prevent the execution other finalize() method and consequently prevent the reclamation of these object's memory.

For objects that are allocated in a javax.realtime.ScopedMemory, the finalize() methods will be called when this scoped memory is exited by the last thread. Unlike HeapMemory, which is controlled by the garbage collector, ScopedMemory provides a defined execution point for the finalize() mehods and it is therefore safer to use finalize() here.

Overrides:

finalize in class Object

Throws:

IOException

getFD

public final FileDescriptor getFD()
                           throws IOException

This method returns a FileDescriptor object representing the underlying native file handle of the file this stream is reading from

Returns:

A FileDescriptor for this stream

Throws:

IOException - If an error occurs

read

public int read()
         throws IOException

This method reads an unsigned byte from the input stream and returns it as an int in the range of 0-255. This method also will return -1 if the end of the stream has been reached.

This method will block until the byte can be read.

Specified by:

read in class InputStream

Returns:

The byte read or -1 if end of stream

Throws:

IOException - If an error occurs

read

public int read(byte[] buf)
         throws IOException

This method reads bytes from a stream and stores them into a caller supplied buffer. This method attempts to completely fill the buffer, but can return before doing so. The actual number of bytes read is returned as an int. A -1 is returned to indicate the end of the stream.

This method will block until some data can be read.

This method operates by calling an overloaded read method like so: read(buf, 0, buf.length)

Overrides:

read in class InputStream

Parameters:

buf - The buffer into which the bytes read will be stored.

Returns:

The number of bytes read or -1 if end of stream.

Throws:

IOException - If an error occurs.

read

public int read(byte[] buf,
                int offset,
                int len)
         throws IOException

This method read bytes from a stream and stores them into a caller supplied buffer. It starts storing the data at index offset into the buffer and attempts to read len bytes. This method can return before reading the number of bytes requested. The actual number of bytes read is returned as an int. A -1 is returned to indicate the end of the stream.

This method will block until some data can be read.

Overrides:

read in class InputStream

Parameters:

buf - The array into which the bytes read should be stored

offset - The offset into the array to start storing bytes

len - The requested number of bytes to read

Returns:

The actual number of bytes read, or -1 if end of stream.

Throws:

IOException - If an error occurs.

skip

public long skip(long numBytes)
          throws IOException

This method skips the specified number of bytes in the stream. It returns the actual number of bytes skipped, which may be less than the requested amount.

Overrides:

skip in class InputStream

Parameters:

numBytes - The requested number of bytes to skip

Returns:

The actual number of bytes skipped.

Throws:

IOException - If an error occurs

getChannel

public FileChannel getChannel()

This method creates a java.nio.channels.FileChannel. Nio does not allow one to create a file channel directly. A file channel must be created by first creating an instance of Input/Output/RandomAccessFile and invoking the getChannel() method on it.