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FileInputStream.javaAPI DocJava SE 6 API12322Tue Jun 10 00:25:32 BST 2008java.io

FileInputStream

public class FileInputStream extends InputStream
A FileInputStream obtains input bytes from a file in a file system. What files are available depends on the host environment.

FileInputStream is meant for reading streams of raw bytes such as image data. For reading streams of characters, consider using FileReader.

author
Arthur van Hoff
version
1.68, 04/07/06
see
java.io.File
see
java.io.FileDescriptor
see
java.io.FileOutputStream
since
JDK1.0

Fields Summary
private FileDescriptor
fd
private FileChannel
channel
Constructors Summary
public FileInputStream(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. A new FileDescriptor object is created to represent this file connection.

First, if there is a security manager, its checkRead method is called with the name argument as its argument.

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 FileNotFoundException is thrown.

param
name the system-dependent file name.
exception
FileNotFoundException if the file does not exist, is a directory rather than a regular file, or for some other reason cannot be opened for reading.
exception
SecurityException if a security manager exists and its checkRead method denies read access to the file.
see
java.lang.SecurityManager#checkRead(java.lang.String)


                                                                                                                                                                                                                                                          
         
        this(name != null ? new File(name) : null);
    
public FileInputStream(File file)
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, if there is a security manager, its checkRead method is called with the path represented by the file argument as its argument.

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 FileNotFoundException is thrown.

param
file the file to be opened for reading.
exception
FileNotFoundException if the file does not exist, is a directory rather than a regular file, or for some other reason cannot be opened for reading.
exception
SecurityException if a security manager exists and its checkRead method denies read access to the file.
see
java.io.File#getPath()
see
java.lang.SecurityManager#checkRead(java.lang.String)

	String name = (file != null ? file.getPath() : null);
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	    security.checkRead(name);
	}
        if (name == null) {
            throw new NullPointerException();
        }
	fd = new FileDescriptor();
	open(name);
    
public FileInputStream(FileDescriptor fdObj)
Creates a FileInputStream by using the file descriptor fdObj, which represents an existing connection to an actual file in the file system.

If there is a security manager, its checkRead method is called with the file descriptor fdObj as its argument to see if it's ok to read the file descriptor. If read access is denied to the file descriptor a SecurityException is thrown.

If fdObj is null then a NullPointerException is thrown.

param
fdObj the file descriptor to be opened for reading.
throws
SecurityException if a security manager exists and its checkRead method denies read access to the file descriptor.
see
SecurityManager#checkRead(java.io.FileDescriptor)

	SecurityManager security = System.getSecurityManager();
	if (fdObj == null) {
	    throw new NullPointerException();
	}
	if (security != null) {
	    security.checkRead(fdObj);
	}
	fd = fdObj;
    
Methods Summary
public native intavailable()
Returns an estimate of the number of remaining bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream. The next invocation might be the same thread or another thread. A single read or skip of this many bytes will not block, but may read or skip fewer bytes.

In some cases, a non-blocking read (or skip) may appear to be blocked when it is merely slow, for example when reading large files over slow networks.

return
an estimate of the number of remaining bytes that can be read (or skipped over) from this input stream without blocking.
exception
IOException if this file input stream has been closed by calling {@code close} or an I/O error occurs.

public voidclose()
Closes this file input stream and releases any system resources associated with the stream.

If this stream has an associated channel then the channel is closed as well.

exception
IOException if an I/O error occurs.
revised
1.4
spec
JSR-51

        if (channel != null)
            channel.close();
        close0();
    
private native voidclose0()

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

exception
IOException if an I/O error occurs.
see
java.io.FileInputStream#close()

	initIDs();
    
	if (fd != null) {
	    if (fd != fd.in) {
		close();
	    }
	}
    
public java.nio.channels.FileChannelgetChannel()
Returns the unique {@link java.nio.channels.FileChannel FileChannel} object associated with this file input stream.

The initial {@link java.nio.channels.FileChannel#position() position} of the returned channel will be equal to the number of bytes read from the file so far. Reading bytes from this stream will increment the channel's position. Changing the channel's position, either explicitly or by reading, will change this stream's file position.

return
the file channel associated with this file input stream
since
1.4
spec
JSR-51

	synchronized (this) {
	    if (channel == null)
		channel = FileChannelImpl.open(fd, true, false, this);
	    return channel;
	}
    
public final java.io.FileDescriptorgetFD()
Returns the FileDescriptor object that represents the connection to the actual file in the file system being used by this FileInputStream.

return
the file descriptor object associated with this stream.
exception
IOException if an I/O error occurs.
see
java.io.FileDescriptor

	if (fd != null) return fd;
	throw new IOException();
    
private static native voidinitIDs()

private native voidopen(java.lang.String name)
Opens the specified file for reading.

param
name the name of the file

public native intread()
Reads a byte of data from this input stream. This method blocks if no input is yet available.

return
the next byte of data, or -1 if the end of the file is reached.
exception
IOException if an I/O error occurs.

public intread(byte[] b)
Reads up to b.length bytes of data from this input stream into an array of bytes. This method blocks until some input is available.

param
b the buffer into which the data is read.
return
the total number of bytes read into the buffer, or -1 if there is no more data because the end of the file has been reached.
exception
IOException if an I/O error occurs.

	return readBytes(b, 0, b.length);
    
public intread(byte[] b, int off, int len)
Reads up to len bytes of data from this input stream into an array of bytes. If len is not zero, the method blocks until some input is available; otherwise, no bytes are read and 0 is returned.

param
b the buffer into which the data is read.
param
off the start offset in the destination array b
param
len the maximum number of bytes read.
return
the total number of bytes read into the buffer, or -1 if there is no more data because the end of the file has been reached.
exception
NullPointerException If b is null.
exception
IndexOutOfBoundsException If off is negative, len is negative, or len is greater than b.length - off
exception
IOException if an I/O error occurs.

	return readBytes(b, off, len);
    
private native intreadBytes(byte[] b, int off, int len)
Reads a subarray as a sequence of bytes.

param
b the data to be written
param
off the start offset in the data
param
len the number of bytes that are written
exception
IOException If an I/O error has occurred.

public native longskip(long n)
Skips over and discards n bytes of data from the input stream.

The skip method may, for a variety of reasons, end up skipping over some smaller number of bytes, possibly 0. If n is negative, an IOException is thrown, even though the skip method of the {@link InputStream} superclass does nothing in this case. The actual number of bytes skipped is returned.

This method may skip more bytes than are remaining in the backing file. This produces no exception and the number of bytes skipped may include some number of bytes that were beyond the EOF of the backing file. Attempting to read from the stream after skipping past the end will result in -1 indicating the end of the file.

param
n the number of bytes to be skipped.
return
the actual number of bytes skipped.
exception
IOException if n is negative, if the stream does not support seek, or if an I/O error occurs.