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:

  • 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.

      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:

    • 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.

      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:

    • 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:

  • 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:

    • 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:

    • 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:

    • 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:

    • 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