FileInputStream

The FileInputStream class represents a byte stream that reads data from a file in a file system. What files are available depends on the host environment. The file can be specified using a FileDescriptor, a File object, or a String that represents a pathname. All of the constructors can throw a SecurityException if the application does not have permission to read from the specified file:

public FileInputStream(String name) throws FileNotFoundException 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.

public FileInputStream(File file) throws FileNotFoundException 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.

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.

FileInputStream provides a low-level interface for reading data from a file. You should wrap a FileInputStream with a DataInputStream if you need a higher-level interface that can handle reading strings and binary data. You should also think about wrapping a FileInputStream with a BufferedInputStream to increase reading efficiency.

public int read() throws IOException reads a byte of data from this input stream. This method blocks if no input is yet available. If an I/O error occurs,an IOException will be thrown.
public int read(byte[] b) throws IOException 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. Returns 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. If b is null, a NullPointerException is thrown. If an I/O error occurs, an IOException is thrown.
public int read(byte[] b, int off, int len) throws IOException reads up to len bytes of data from this input stream into an array of bytes. This method blocks until some input is available. Returns 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.

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 an I/O error occurs, an IOException is thrown.

public int available() throws IOException returns the number of bytes that can be read from this file input stream without blocking. Returns the number of bytes that can be read from this file input stream without blocking. An IOException is thrown if an I/O error occurs.

Data must be read sequentially from a FileInputStream; you can skip forward, but you cannot move back. If you need random access to file data, use the RandomAccessFile class instead.

public long skip(long n) throws IOException skips over and discards n bytes of data from the input stream. Returns the actual number of bytes skipped. An IOException is thrown if n is negative, or if an I/O error occurs.

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 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.

Do not forget to close and release the resource you do not need to use.

public void close() throws IOException 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. An IOException is thrown if an I/O error occurs.
protected void finalize() throws IOException ensures that the close method of this file input stream is called when there are no more references to it. An IOException is thrown if an I/O error occurs.

Misc Mthods:

public final FileDescriptor getFD() throws IOException returns the FileDescriptor object that represents the connection to the actual file in the file system being used by this FileInputStream. An IOException is thrown if an I/O error occurs.
public FileChannel getChannel() returns the unique FileChannel object associated with this file input stream. The initial 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.

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