Package org.apache.derby.impl.jdbc

Class PositionedStoreStream

  • All Implemented Interfaces:
    java.io.Closeable, java.lang.AutoCloseable, PositionedStream, Resetable
    public class PositionedStoreStream
extends java.io.InputStream
implements PositionedStream, Resetable
    A wrapper-stream able to reposition the underlying store stream.

    Where a user expects the underlying stream to be at a given position, reposition(long) must be called with the expected position first. A use case for this scenario is the LOB objects, where you can request a stream and at the same time (this does not mean concurrently) query the LOB about its length or ask to get a part of the LOB returned. Such multiplexed operations must result in consistent and valid data, and to achieve this the underlying store stream must be able to reposition itself. Synchronization: Access to instances of this class must be externally synchronized on the connection synchronization object. There are two reasons for this:

    • Access to store must be single threaded.
    • This class is not thread safe, and calling the various methods from different threads concurrently can result in inconsistent position values. To avoid redundant internal synchronization, this class assumes and requires external synchronization (also called client-side locking).
    See Also:
    EmbedConnection.getConnectionSynchronization()

    • Field Summary

      Fields 
      Modifier and Type Field Description
      private long pos
      Position of the underlying store stream.
      private java.io.InputStream stream
      Underlying store stream serving bytes.

    • Constructor Summary

      Constructors 
      Constructor Description
      PositionedStoreStream​(java.io.InputStream in)
      Creates a positioned store stream on top of the specified resettable stream.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      java.io.InputStream asInputStream()
      Returns a reference to self as an InputStream.
      void closeStream()
      Closes the resettable stream.
      long getPosition()
      Returns the current position of the underlying store stream.
      void initStream()
      Initialize the resettable stream for use.
      int read()
      Reads a single byte from the underlying stream.
      int read​(byte[] b)
      Reads a number of bytes from the underlying stream and stores them in the specified byte array.
      int read​(byte[] b, int off, int len)
      Reads a number of bytes from the underlying stream and stores them in the specified byte array at the specified offset.
      void reposition​(long requestedPos)
      Repositions the underlying store stream to the requested position.
      void resetStream()
      Resets the resettable stream.
      long skip​(long toSkip)
      Skips up to the specified number of bytes from the underlying stream.

      • Methods inherited from class java.io.InputStream

        available, close, mark, markSupported, nullInputStream, readAllBytes, readNBytes, readNBytes, reset, transferTo

      • Methods inherited from class java.lang.Object

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

    • Field Detail

      • stream

        private final java.io.InputStream stream
        Underlying store stream serving bytes.

      • pos

        private long pos
        Position of the underlying store stream. Note that the position is maintained by this class, not the underlying store stream itself. Future improvement: Add this functionality to the underlying store stream itself to avoid another level in the stream stack.

    • Constructor Detail

      • PositionedStoreStream

        public PositionedStoreStream​(java.io.InputStream in)
                      throws java.io.IOException,
                             StandardException
        Creates a positioned store stream on top of the specified resettable stream.

        Upon creation, the underlying stream is initiated and reset to make sure the states of the streams are in sync with each other.

        Parameters:
        in - a Resetable-stream
        Throws:
        java.io.IOException
        StandardException

    • Method Detail

      • read

        public int read​(byte[] b)
         throws java.io.IOException
        Reads a number of bytes from the underlying stream and stores them in the specified byte array.
        Overrides:
        read in class java.io.InputStream
        Returns:
        The actual number of bytes read, or -1 if the end of the stream is reached.
        Throws:
        java.io.IOException - if an I/O error occurs

      • read

        public int read​(byte[] b,
                int off,
                int len)
         throws java.io.IOException
        Reads a number of bytes from the underlying stream and stores them in the specified byte array at the specified offset.
        Overrides:
        read in class java.io.InputStream
        Returns:
        The actual number of bytes read, or -1 if the end of the stream is reached.
        Throws:
        java.io.IOException - if an I/O error occurs

      • read

        public int read()
         throws java.io.IOException
        Reads a single byte from the underlying stream.
        Specified by:
        read in class java.io.InputStream
        Returns:
        The next byte of data, or -1 if the end of the stream is reached.
        Throws:
        java.io.IOException - if an I/O error occurs

      • skip

        public long skip​(long toSkip)
          throws java.io.IOException
        Skips up to the specified number of bytes from the underlying stream.
        Overrides:
        skip in class java.io.InputStream
        Returns:
        The actual number of bytes skipped.
        Throws:
        java.io.IOException - if an I/O error occurs

      • reposition

        public void reposition​(long requestedPos)
                throws java.io.IOException,
                       StandardException
        Repositions the underlying store stream to the requested position.

        Repositioning is required because there can be several uses of the store stream, which changes the position of it. If a class is dependent on the underlying stream not changing its position, it must call reposition with the position it expects before using the stream again.

        If the repositioning fails because the stream is exhausted, most likely because of an invalid position specified by the user, the stream is reset to position zero and the EOFException is rethrown.

        Specified by:
        reposition in interface PositionedStream
        Parameters:
        requestedPos - requested byte position, first position is 0
        Throws:
        java.io.EOFException - if the stream is exhausted before the requested position is reached
        java.io.IOException - if reading from the store stream fails
        StandardException - if resetting the store in stream fails, or some other exception happens in store
        See Also:
        getPosition()

      • getPosition

        public long getPosition()
        Returns the current position of the underlying store stream.
        Specified by:
        getPosition in interface PositionedStream
        Returns:
        Current byte position of the store stream.

      • asInputStream

        public java.io.InputStream asInputStream()
        Description copied from interface: PositionedStream
        Returns a reference to self as an InputStream.

        This method is not allowed to return null.

        Specified by:
        asInputStream in interface PositionedStream
        Returns:
        An InputStream reference to self.