Interface Cursor

All Known Implementing Classes:
TransportCursor

public interface Cursor
The Cursor object is used to acquire bytes from a given source. This provides a cursor style reading of bytes from a stream in that it will allow the reader to move the cursor back if the amount of bytes read is too much. Allowing the cursor to move ensures that excess bytes back be placed back in the stream.

This is used when parsing input from a stream as it ensures that on arrival at a terminal token any excess bytes can be placed back in to the stream. This allows data to be read efficiently in large chunks from blocking streams such as sockets.

Author:
Niall Gallagher
See Also:
  • Method Summary

    Modifier and Type
    Method
    Description
    boolean
    Determines whether the cursor is still open.
    boolean
    Determines whether the cursor is ready for reading.
    void
    push(byte[] data)
    Pushes the provided data on to the cursor.
    void
    push(byte[] data, int off, int len)
    Pushes the provided data on to the cursor.
    int
    read(byte[] data)
    Reads a block of bytes from the underlying stream.
    int
    read(byte[] data, int off, int len)
    Reads a block of bytes from the underlying stream.
    int
    Provides the number of bytes that can be read from the stream without blocking.
    int
    reset(int len)
    Moves the cursor backward within the stream.
  • Method Details

    • isOpen

      boolean isOpen() throws IOException
      Determines whether the cursor is still open. The cursor is considered open if there are still bytes to read. If there is still bytes buffered and the underlying transport is closed then the cursor is still considered open.
      Returns:
      true if the read method does not return a -1 value
      Throws:
      IOException
    • isReady

      boolean isReady() throws IOException
      Determines whether the cursor is ready for reading. When the cursor is ready then it guarantees that some amount of bytes can be read from the underlying stream without blocking.
      Returns:
      true if some data can be read without blocking
      Throws:
      IOException
    • ready

      int ready() throws IOException
      Provides the number of bytes that can be read from the stream without blocking. This is typically the number of buffered or available bytes within the stream. When this reaches zero then the cursor may perform a blocking read.
      Returns:
      the number of bytes that can be read without blocking
      Throws:
      IOException
    • read

      int read(byte[] data) throws IOException
      Reads a block of bytes from the underlying stream. This will read up to the requested number of bytes from the underlying stream. If there are no ready bytes on the stream this can return zero, representing the fact that nothing was read.
      Parameters:
      data - this is the array to read the bytes in to
      Returns:
      this returns the number of bytes read from the stream
      Throws:
      IOException
    • read

      int read(byte[] data, int off, int len) throws IOException
      Reads a block of bytes from the underlying stream. This will read up to the requested number of bytes from the underlying stream. If there are no ready bytes on the stream this can return zero, representing the fact that nothing was read.
      Parameters:
      data - this is the array to read the bytes in to
      off - this is the offset to begin writing the bytes to
      len - this is the number of bytes that are requested
      Returns:
      this returns the number of bytes read from the stream
      Throws:
      IOException
    • push

      void push(byte[] data) throws IOException
      Pushes the provided data on to the cursor. Data pushed on to the cursor will be the next data read from the cursor. This complements the reset method which will reset the cursors position on a stream. Allowing data to be pushed on to the cursor allows more flexibility.
      Parameters:
      data - this is the data to be pushed on to the cursor
      Throws:
      IOException
    • push

      void push(byte[] data, int off, int len) throws IOException
      Pushes the provided data on to the cursor. Data pushed on to the cursor will be the next data read from the cursor. This complements the reset method which will reset the cursors position on a stream. Allowing data to be pushed on to the cursor allows more flexibility.
      Parameters:
      data - this is the data to be pushed on to the cursor
      off - this is the offset to begin reading the bytes
      len - this is the number of bytes that are to be used
      Throws:
      IOException
    • reset

      int reset(int len) throws IOException
      Moves the cursor backward within the stream. This ensures that any bytes read from the last read can be pushed back in to the stream so that they can be read again. This will throw an exception if the reset can not be performed.
      Parameters:
      len - this is the number of bytes to reset back
      Returns:
      this is the number of bytes that have been reset
      Throws:
      IOException