Package java.io

Class InputStream

  • All Implemented Interfaces:
    Closeable, AutoCloseable, Modified
    Direct Known Subclasses:
    DummyInputStream, SCIInputStream, UARTInputStream, UARTInputStream
    public abstract class InputStream
extends Object
implements Closeable, Modified
    A readable source of bytes.

    Use InputStreamReader to adapt a byte stream like this one into a character stream.

    Most clients should wrap their input stream with BufferedInputStream. Callers that do only bulk reads may omit buffering.

    Some implementations support marking a position in the input stream and resetting back to this position later. Implementations that don't return false from markSupported() and throw an IOException when reset() is called.

    Subclassing InputStream

    Subclasses that decorate another input stream should consider subclassing FilterInputStream, which delegates all calls to the source input stream.

    All input stream subclasses should override both read() and read(byte[],int,int). The three argument overload is necessary for bulk access to the data. This is much more efficient than byte-by-byte access.

    See Also:
    OutputStream

    • Constructor Summary

      Constructors 
      Constructor Description
      InputStream()
      This constructor does nothing.

    • Method Summary

      All Methods Instance Methods Abstract Methods Concrete Methods 
      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.
      void mark​(int readlimit)
      Sets a mark position in this InputStream.
      boolean markSupported()
      Indicates whether this stream supports the mark() and reset() methods.
      abstract 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)
      Equivalent to read(buffer, 0, buffer.length).
      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.
      void reset()
      Resets this stream to the last marked location.

    • Constructor Detail

      • InputStream

        public InputStream()
        This constructor does nothing. It is provided for signature compatibility.

    • Method Detail

      • available

        public int available()
              throws IOException
        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.

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

      • close

        public void close()
           throws IOException
        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
        Throws:
        IOException - if an error occurs while closing this stream.

      • mark

        public void mark​(int readlimit)
        Sets a mark position in this InputStream. The parameter readlimit indicates how many bytes can be read before the mark is invalidated. Sending reset() will reposition the stream back to the marked position provided readLimit has not been surpassed.

        This default implementation does nothing and concrete subclasses must provide their own implementation.

        Parameters:
        readlimit - the number of bytes that can be read from this stream before the mark is invalidated.
        See Also:
        markSupported(), reset()

      • markSupported

        public boolean markSupported()
        Indicates whether this stream supports the mark() and reset() methods. The default implementation returns false.
        Returns:
        always false.
        See Also:
        mark(int), reset()

      • read

        public abstract int read()
                  throws IOException
        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.
        Returns:
        Byte read.
        Throws:
        IOException - if the stream is closed or another IOException occurs.

      • read

        public int read​(byte[] buffer)
         throws IOException
        Equivalent to read(buffer, 0, buffer.length).
        Parameters:
        buffer - Buffer to store read values into.
        Returns:
        Number of bytes read.
        Throws:
        IOException - if the stream is closed or another IOException occurs.

      • read

        public int read​(byte[] buffer,
                int byteOffset,
                int byteCount)
         throws IOException
        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.
        Parameters:
        buffer - Buffer to store read values into.
        byteOffset - Byte offset in buffer where first value is stored.
        byteCount - Number of bytes to read.
        Returns:
        Number of bytes read.
        Throws:
        IndexOutOfBoundsException - if byteOffset < 0 || byteCount < 0 || byteOffset + byteCount > buffer.length.
        IOException - if the stream is closed or another IOException occurs.

      • reset

        public void reset()
           throws IOException
        Resets this stream to the last marked location. Throws an IOException if the number of bytes read since the mark has been set is greater than the limit provided to mark, or if no mark has been set.

        This implementation always throws an IOException and concrete subclasses should provide the proper implementation.

        Throws:
        IOException - if this stream is closed or another IOException occurs.