Package java.io

Class FileInputStream

java.lang.Object
java.io.InputStream
java.io.FileInputStream
All Implemented Interfaces:
Closeable, AutoCloseable
public class FileInputStream
extends InputStream
An input stream that reads bytes from a file. 
   
   File file = ...
   InputStream in = null;
   try {
     in = new BufferedInputStream(new FileInputStream(file));
     ...
   } finally {
     if (in != null) {
       in.close();
     }
   }

This stream is not buffered. Most callers should wrap this stream with a BufferedInputStream.

Use FileReader to read characters, as opposed to bytes, from a file.

See Also:
BufferedInputStream, FileOutputStream

  • Constructor Summary

    Constructors
    Constructor Description
    FileInputStream​(File file)
    Constructs a new FileInputStream that reads from file.
    FileInputStream​(FileDescriptor fd)
    Constructs a new FileInputStream that reads from fd.
    FileInputStream​(String path)
    Equivalent to new FileInputStream(new File(path)).

  • Method Summary

    Modifier and Type Method Description
    int available()
    Returns an estimated number of bytes that can be read or skipped without blocking for more input.
    void close()
    Closes this stream.
    protected void finalize()
    Ensures that all resources for this stream are released when it is about to be garbage collected.
    FileChannel getChannel()
    Returns a read-only FileChannel that shares its position with this stream.
    FileDescriptor getFD()
    Returns the underlying file descriptor.
    int read()
    Reads a single byte from this stream and returns it as an integer in the range from 0 to 255.
    int read​(byte[] buffer, int byteOffset, int byteCount)
    Reads up to byteCount bytes from this stream and stores them in the byte array buffer starting at byteOffset.
    long skip​(long byteCount)
    Skips at most n bytes in this stream.

    Methods inherited from class java.io.InputStream

    mark, markSupported, read, reset

    Methods inherited from class java.lang.Object

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

  • Constructor Details

    • FileInputStream

      public FileInputStream​(File file) throws FileNotFoundException
      Constructs a new FileInputStream that reads from file.
      Parameters:
      file - the file from which this stream reads.
      Throws:
      FileNotFoundException - if file does not exist.

    • FileInputStream

      public FileInputStream​(FileDescriptor fd)
      Constructs a new FileInputStream that reads from fd.
      Parameters:
      fd - the FileDescriptor from which this stream reads.
      Throws:
      NullPointerException - if fd is null.

    • FileInputStream

      public FileInputStream​(String path) throws FileNotFoundException
      Equivalent to new FileInputStream(new File(path)).
      Throws:
      FileNotFoundException

  • Method Details

    • available

      public int available() throws IOException
      Description copied from class: InputStream
      Returns an estimated number of bytes that can be read or skipped without blocking for more input.

      Note that this method provides such a weak guarantee that it is not very useful in practice.

      Firstly, the guarantee is "without blocking for more input" rather than "without blocking": a read may still block waiting for I/O to complete — the guarantee is merely that it won't have to wait indefinitely for data to be written. The result of this method should not be used as a license to do I/O on a thread that shouldn't be blocked.

      Secondly, the result is a conservative estimate and may be significantly smaller than the actual number of bytes available. In particular, an implementation that always returns 0 would be correct. In general, callers should only use this method if they'd be satisfied with treating the result as a boolean yes or no answer to the question "is there definitely data ready?".

      Thirdly, the fact that a given number of bytes is "available" does not guarantee that a read or skip will actually read or skip that many bytes: they may read or skip fewer.

      It is particularly important to realize that you must not use this method to size a container and assume that you can read the entirety of the stream without needing to resize the container. Such callers should probably write everything they read to a ByteArrayOutputStream and convert that to a byte array. Alternatively, if you're reading from a file, File.length() returns the current length of the file (though assuming the file's length can't change may be incorrect, reading a file is inherently racy).

      The default implementation of this method in InputStream always returns 0. Subclasses should override this method if they are able to indicate the number of bytes available.

      Overrides:
      available in class InputStream
      Returns:
      the estimated number of bytes available
      Throws:
      IOException - if this stream is closed or an error occurs

    • close

      public void close() throws IOException
      Description copied from class: InputStream
      Closes this stream. Concrete implementations of this class should free any resources during close. This implementation does nothing.
      Specified by:
      close in interface AutoCloseable
      Specified by:
      close in interface Closeable
      Overrides:
      close in class InputStream
      Throws:
      IOException - if an error occurs while closing this stream.

    • finalize

      protected void finalize() throws IOException
      Ensures that all resources for this stream are released when it is about to be garbage collected.
      Overrides:
      finalize in class Object
      Throws:
      IOException - if an error occurs attempting to finalize this stream.

    • getChannel

      public FileChannel getChannel()
      Returns a read-only FileChannel that shares its position with this stream.

    • getFD

      public final FileDescriptor getFD() throws IOException
      Returns the underlying file descriptor.
      Throws:
      IOException

    • read

      public int read() throws IOException
      Description copied from class: InputStream
      Reads a single byte from this stream and returns it as an integer in the range from 0 to 255. Returns -1 if the end of the stream has been reached. Blocks until one byte has been read, the end of the source stream is detected or an exception is thrown.
      Specified by:
      read in class InputStream
      Throws:
      IOException - if the stream is closed or another IOException occurs.

    • read

      public int read​(byte[] buffer, int byteOffset, int byteCount) throws IOException
      Description copied from class: InputStream
      Reads up to byteCount bytes from this stream and stores them in the byte array buffer starting at byteOffset. Returns the number of bytes actually read or -1 if the end of the stream has been reached.
      Overrides:
      read in class InputStream
      Throws:
      IOException - if the stream is closed or another IOException occurs.

    • skip

      public long skip​(long byteCount) throws IOException
      Description copied from class: InputStream
      Skips at most n bytes in this stream. This method does nothing and returns 0 if n is negative, but some subclasses may throw.

      Note the "at most" in the description of this method: this method may choose to skip fewer bytes than requested. Callers should always check the return value.

      This default implementation reads bytes into a temporary buffer. Concrete subclasses should provide their own implementation.

      Overrides:
      skip in class InputStream
      Parameters:
      byteCount - the number of bytes to skip.
      Returns:
      the number of bytes actually skipped.
      Throws:
      IOException - if this stream is closed or another IOException occurs.