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SequenceInputStream


java.io

Class SequenceInputStream

  • All Implemented Interfaces:
    Closeable, AutoCloseable


    public class SequenceInputStream
    extends InputStream
    Concatenates two or more existing InputStreams. Reads are taken from the first stream until it ends, then the next stream is used, until the last stream returns end of file.
    • Method Summary

      Methods
      Modifier and Type Method and Description
      int available()
      Returns an estimated number of bytes that can be read or skipped without blocking for more input.
      void close()
      Closes all streams in this sequence of input stream.
      int read()
      Reads a single byte from this sequence of input streams and returns it as an integer in the range from 0 to 255.
      int read(byte[] buffer, int offset, int count)
      Reads at most count bytes from this sequence of input streams and stores them in the byte array buffer starting at offset.
    • Constructor Detail

      • SequenceInputStream

        public SequenceInputStream(InputStream s1,
                           InputStream s2)
        Constructs a new SequenceInputStream using the two streams s1 and s2 as the sequence of streams to read from.
        Parameters:
        s1 - the first stream to get bytes from.
        s2 - the second stream to get bytes from.
        Throws:
        NullPointerException - if s1 is null.
      • SequenceInputStream

        public SequenceInputStream(Enumeration<? extends InputStream> e)
        Constructs a new SequenceInputStream using the elements returned from Enumeration e as the stream sequence. The instances returned by e.nextElement() must be of type InputStream.
        Parameters:
        e - the enumeration of InputStreams to get bytes from.
        Throws:
        NullPointerException - if any of the elements in e is null.
    • Method Detail

      • 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
      • read

        public int read()
                 throws IOException
        Reads a single byte from this sequence of input streams and returns it as an integer in the range from 0 to 255. It tries to read from the current stream first; if the end of this stream has been reached, it reads from the next one. Blocks until one byte has been read, the end of the last input stream in the sequence has been reached, or an exception is thrown.
        Specified by:
        read in class InputStream
        Returns:
        the byte read or -1 if either the end of the last stream in the sequence has been reached or this input stream sequence is closed.
        Throws:
        IOException - if an error occurs while reading the current source input stream.
      • read

        public int read(byte[] buffer,
               int offset,
               int count)
                 throws IOException
        Reads at most count bytes from this sequence of input streams and stores them in the byte array buffer starting at offset. Blocks only until at least 1 byte has been read, the end of the stream has been reached, or an exception is thrown.

        This SequenceInputStream shows the same behavior as other InputStreams. To do this it will read only as many bytes as a call to read on the current substream returns. If that call does not return as many bytes as requested by count, it will not retry to read more on its own because subsequent reads might block. This would violate the rule that it will only block until at least one byte has been read.

        If a substream has already reached the end when this call is made, it will close that substream and start with the next one. If there are no more substreams it will return -1.

        Overrides:
        read in class InputStream
        Parameters:
        buffer - the array in which to store the bytes read.
        offset - the initial position in buffer to store the bytes read from this stream.
        count - the maximum number of bytes to store in buffer.
        Returns:
        the number of bytes actually read; -1 if this sequence of streams is closed or if the end of the last stream in the sequence has been reached.
        Throws:
        IndexOutOfBoundsException - if offset < 0 or count < 0, or if offset + count is greater than the size of buffer.
        IOException - if an I/O error occurs.
        NullPointerException - if buffer is null.


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