# Class FileInputStream

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

All Implemented Interfaces:
  `Closeable`, `AutoCloseable`

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`.

API Note:
  The `close()` method should be called to release resources used by this stream, either directly, or with the `try`-with-resources statement.
Implementation Requirements:
  Subclasses are responsible for the cleanup of resources acquired by the subclass. Subclasses requiring that resource cleanup take place after a stream becomes unreachable should use `Cleaner` or some other mechanism.
Since:
  1.0
See Also:
  - `File`
  - `FileDescriptor`
  - `FileOutputStream`
  - `Files.newInputStream(java.nio.file.Path, java.nio.file.OpenOption...)`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `FileInputStream(File file)`
  Creates a `FileInputStream` to read from an existing file represented by the `File` object `file`.
  `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.
  `FileInputStream(String name)`
  Creates a `FileInputStream` to read from an existing file named by the path name `name`.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `int`
  `available()`
  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.
  `void`
  `close()`
  Closes this file input stream and releases any system resources associated with the stream.
  `FileChannel`
  `getChannel()`
  Returns the unique `FileChannel` object associated with this file input stream.
  `final FileDescriptor`
  `getFD()`
  Returns the `FileDescriptor` object that represents the connection to the actual file in the file system being used by this `FileInputStream`.
  `int`
  `read()`
  Reads a byte of data from this input stream.
  `int`
  `read(byte[] b)`
  Reads up to `b.length` bytes of data from this input stream into an array of bytes.
  `int`
  `read(byte[] b, int off, int len)`
  Reads up to `len` bytes of data from this input stream into an array of bytes.
  `byte[]`
  `readNBytes(int len)`
  Reads up to a specified number of bytes from the input stream.
  `long`
  `skip(long n)`
  Skips over and discards `n` bytes of data from the input stream.

  ### Methods declared in class java.io.InputStream

  `mark, markSupported, nullInputStream, readAllBytes, readNBytes, reset, skipNBytes, transferTo`

  ### Methods declared in class java.lang.Object

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

- ## Constructor Details

  - ### FileInputStream

    public FileInputStream(String name) throws FileNotFoundException
    Creates a `FileInputStream` to read from an existing file named by the path name `name`. Symbolic links are automatically redirected to the target of the link. A new `FileDescriptor` object is created to represent this file connection.

    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.

    Parameters:
      `name` - the system-dependent file name.
    Throws:
      `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.

  - ### FileInputStream

    public FileInputStream(File file) throws FileNotFoundException
    Creates a `FileInputStream` to read from an existing file represented by the `File` object `file`. Symbolic links are automatically redirected to the target of the link. A new `FileDescriptor` object is created to represent this file connection.

    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.

    Parameters:
      `file` - the file to be opened for reading.
    Throws:
      `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.
    See Also:
      - `File.getPath()`

  - ### FileInputStream

    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 `fdObj` is null then a `NullPointerException` is thrown.

    This constructor does not throw an exception if `fdObj` is `invalid`. However, if the methods are invoked on the resulting stream to attempt I/O on the stream, an `IOException` is thrown.

    Parameters:
      `fdObj` - the file descriptor to be opened for reading.

- ## Method Details

  - ### read

    public int read() throws IOException
    Reads a byte of data from this input stream. This method blocks if no input is yet available.
    Specified by:
      `read` in class `InputStream`
    Returns:
      the next byte of data, or `-1` if the end of the file is reached.
    Throws:
      `IOException` - if an I/O error occurs.

  - ### read

    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.
    Overrides:
      `read` in class `InputStream`
    Parameters:
      `b` - the buffer into which the data is read.
    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.
    Throws:
      `IOException` - if an I/O error occurs.
    See Also:
      - `InputStream.read(byte[], int, int)`

  - ### read

    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. If `len` is not zero, the method blocks until some input is available; otherwise, no bytes are read and `0` is returned.
    Overrides:
      `read` in class `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:
      `NullPointerException` - If `b` is `null`.
      `IndexOutOfBoundsException` - If `off` is negative, `len` is negative, or `len` is greater than `b.length - off`
      `IOException` - if an I/O error occurs.
    See Also:
      - `InputStream.read()`

  - ### readNBytes

    public byte[] readNBytes(int len) throws IOException
    Description copied from class: `InputStream`
    Reads up to a specified number of bytes from the input stream. This method blocks until the requested number of bytes has been read, end of stream is detected, or an exception is thrown. This method does not close the input stream.

    The length of the returned array equals the number of bytes read from the stream. If `len` is zero, then no bytes are read and an empty byte array is returned. Otherwise, up to `len` bytes are read from the stream. Fewer than `len` bytes may be read if end of stream is encountered.

    When this stream reaches end of stream, further invocations of this method will return an empty byte array.

    Note that this method is intended for simple cases where it is convenient to read the specified number of bytes into a byte array. The total amount of memory allocated by this method is proportional to the number of bytes read from the stream which is bounded by `len`. Therefore, the method may be safely called with very large values of `len` provided sufficient memory is available.

    The behavior for the case where the input stream is asynchronously closed, or the thread interrupted during the read, is highly input stream specific, and therefore not specified.

    If an I/O error occurs reading from the input stream, then it may do so after some, but not all, bytes have been read. Consequently the input stream may not be at end of stream and may be in an inconsistent state. It is strongly recommended that the stream be promptly closed if an I/O error occurs.

    Overrides:
      `readNBytes` in class `InputStream`
    Parameters:
      `len` - the maximum number of bytes to read
    Returns:
      a byte array containing the bytes read from this input stream
    Throws:
      `IOException` - if an I/O error occurs
    Since:
      11

  - ### skip

    public long skip(long n) throws IOException
    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, the method will try to skip backwards. In case the backing file does not support backward skip at its current position, an `IOException` is thrown. The actual number of bytes skipped is returned. If it skips forwards, it returns a positive value. If it skips backwards, it returns a negative value.

    This method may skip more bytes than what 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.

    Overrides:
      `skip` in class `InputStream`
    Parameters:
      `n` - the number of bytes to be skipped.
    Returns:
      the actual number of bytes skipped.
    Throws:
      `IOException` - if n is negative, if the stream does not support seek, or if an I/O error occurs.
    See Also:
      - `InputStream.skipNBytes(long)`

  - ### available

    public int available() throws IOException
    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. Returns 0 when the file position is beyond EOF. 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.

    Overrides:
      `available` in class `InputStream`
    Returns:
      an estimate of the number of remaining bytes that can be read (or skipped over) from this input stream without blocking.
    Throws:
      `IOException` - if this file input stream has been closed by calling `close` or an I/O error occurs.

  - ### close

    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.

    Specified by:
      `close` in interface `AutoCloseable`
    Specified by:
      `close` in interface `Closeable`
    Overrides:
      `close` in class `InputStream`
    API Note:
      Overriding `close()` to perform cleanup actions is reliable only when called directly or when called by try-with-resources.
    Implementation Requirements:
      Subclasses requiring that resource cleanup take place after a stream becomes unreachable should use the `Cleaner` mechanism.

      If this stream has an associated channel then this method will close the channel, which in turn will close this stream. Subclasses that override this method should be prepared to handle possible reentrant invocation.

    Throws:
      `IOException` - if an I/O error occurs.

  - ### getFD

    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`.
    Returns:
      the file descriptor object associated with this stream.
    Throws:
      `IOException` - if an I/O error occurs.
    See Also:
      - `FileDescriptor`

  - ### getChannel

    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.

    Returns:
      the file channel associated with this file input stream
    Since:
      1.4