FileInputStream (Java SE 21 & JDK 21)
Description: declaration: module: java.base, package: java.io, class: FileInputStream
Keywords: java.io.FileInputStream class

Module java.base
Package java.io

# 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` by opening a connection to an actual file, the file named by the `File` object `file` in the file system.
  `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` by opening a connection to an actual file, the file named by the path name `name` in the file system.

- ## 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.
  `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, 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` 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.

    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.
      `SecurityException` - if a security manager exists and its `checkRead` method denies read access to the file.
    See Also:
      - `SecurityManager.checkRead(java.lang.String)`

  - ### FileInputStream

    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.

    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.
      `SecurityException` - if a security manager exists and its `checkRead` method denies read access to the file.
    See Also:
      - `File.getPath()`
      - `SecurityManager.checkRead(java.lang.String)`

  - ### 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 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.

    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.
    Throws:
      `SecurityException` - if a security manager exists and its `checkRead` method denies read access to the file descriptor.
    See Also:
      - `SecurityManager.checkRead(java.io.FileDescriptor)`

- ## 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()`

  - ### 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