java.io
Class FileInputStream

java.lang.Object
  extended by java.io.InputStream
      extended by 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()
          Called on an object by the Virtual Machine at most once, at some point after the Object is determined unreachable but before it is destroyed.
 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
Called on an object by the Virtual Machine at most once, at some point after the Object is determined unreachable but before it is destroyed. You would think that this means it eventually is called on every Object, but this is not necessarily the case. If execution terminates abnormally, garbage collection does not always happen. Thus you cannot rely on this method to always work. For finer control over garbage collection, use references from the java.lang.ref package.

Virtual Machines are free to not call this method if they can determine that it does nothing important; for example, if your class extends Object and overrides finalize to do simply super.finalize().

finalize() will be called by a Thread that has no locks on any Objects, and may be called concurrently. There are no guarantees on the order in which multiple objects are finalized. This means that finalize() is usually unsuited for performing actions that must be thread-safe, and that your implementation must be use defensive programming if it is to always work.

If an Exception is thrown from finalize() during garbage collection, it will be patently ignored and the Object will still be destroyed.

It is allowed, although not typical, for user code to call finalize() directly. User invocation does not affect whether automatic invocation will occur. It is also permitted, although not recommended, for a finalize() method to "revive" an object by making it reachable from normal code again.

Unlike constructors, finalize() does not get called for an object's superclass unless the implementation specifically calls super.finalize().

The default implementation does nothing.

Overrides:
finalize in class Object
Throws:
IOException
See Also:
System.gc(), System.runFinalizersOnExit(boolean), java.lang.ref

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.