Package org.eclipse.persistence.queries

Class CursoredStream

java.lang.Object
org.eclipse.persistence.queries.Cursor
org.eclipse.persistence.queries.CursoredStream
All Implemented Interfaces:
Serializable, Enumeration, Iterator
public class CursoredStream extends Cursor

Purpose: Stream class which is used to deal with large collections returned from TOPLink queries more efficiently.

Responsibilities: Wraps a database result set cursor to provide a stream on the resulting selected objects.

See Also:
Author:
Yvon Lavoie

  • Field Details

    • marker

      protected int marker
      Marker for backing up.

  • Constructor Details

    • CursoredStream

      public CursoredStream()
      INTERNAL: Initialize the state of the stream

    • CursoredStream

      public CursoredStream(org.eclipse.persistence.internal.databaseaccess.DatabaseCall call, CursoredStreamPolicy policy)
      INTERNAL: Initialize the state of the stream

  • Method Details

    • atEnd

      public boolean atEnd() throws DatabaseException
      PUBLIC: Return whether the cursored stream is at its end.
      Throws:
      DatabaseException

    • available

      public int available() throws DatabaseException
      PUBLIC: Returns the number of objects that can be read from this input without blocking.
      Throws:
      DatabaseException

    • buildCountDistinctExpression

      public Expression buildCountDistinctExpression(List includeFields, ExpressionBuilder builder)
      INTERNAL: Must build the count on the primary key fields, not * as * is not allowed if there was a distinct. This require a manually defined operator. added for CR 2900

    • copy

      protected List<Object> copy(int startIndex, int endIndex) throws QueryException
      INTERNAL: Answer a list of the elements of the receiver's collection from startIndex to endIndex.
      Throws:
      QueryException

    • getCursorSize

      protected int getCursorSize() throws DatabaseException, QueryException
      INTERNAL: Retrieve the size of the open cursor by executing a count on the same query as the cursor.
      Specified by:
      getCursorSize in class Cursor
      Throws:
      DatabaseException
      QueryException

    • getInitialReadSize

      protected int getInitialReadSize()
      INTERNAL: Return the threshold for the stream.

    • getMarker

      protected int getMarker()
      INTERNAL: Return the marker used for mark() & reset() operations.

    • getPageSize

      public int getPageSize()
      INTERNAL: Return the page size for the stream.
      Overrides:
      getPageSize in class Cursor

    • getPosition

      public int getPosition()
      INTERNAL: Return the position of the stream inside the object collection
      Specified by:
      getPosition in class Cursor

    • hasMoreElements

      public boolean hasMoreElements()
      PUBLIC: Return whether the cursored stream has any more elements.

    • hasNext

      public boolean hasNext()
      PUBLIC: Return whether the cursored stream has any more elements.

    • mark

      public void mark(int readAheadLimit)
      PUBLIC: Mark the present position in the stream. Subsequent calls to reset() will attempt to reposition the stream to this point.
      Parameters:
      readAheadLimit - Limit on the number of characters that may be read while still preserving the mark. Because the stream's input comes from the database, there is no actual limit, so this argument is ignored.

    • markSupported

      public boolean markSupported()
      PUBLIC: Tests if this input stream supports the mark and reset methods. The markSupported method of InputStream returns false.

    • nextElement

      public Object nextElement()
      PUBLIC: Return the next object from the collection, if beyond the read limit read from the cursor.
      Returns:
      the next object in stream

    • next

      public Object next()
      PUBLIC: Return the next object from the collection, if beyond the read limit read from the cursor.
      Returns:
      the next object in stream

    • nextElements

      public Vector nextElements(int numberOfElements)
      PUBLIC: Return a Vector of at most numberOfElements of the next objects from the collection. If there aren't that many objects left to read, just return what is available.
      Returns:
      the next objects in stream

    • next

      public List<Object> next(int numberOfElements)
      PUBLIC: Return a Vector of at most numberOfElements of the next objects from the collection. If there aren't that many objects left to read, just return what is available.
      Returns:
      the next objects in stream

    • peek

      public Object peek() throws DatabaseException
      PUBLIC: Return the next object in the stream, without incrementing the stream's position.
      Throws:
      DatabaseException

    • read

      public Object read() throws DatabaseException, QueryException
      PUBLIC: This method differs slightly from conventional read() operation on a Java stream. This method return the next object in the collection rather than specifying the number of bytes to be read in. Return the next object from the collection, if beyond the read limit read from the cursor
      Returns:
      - next object in stream
      Throws:
      DatabaseException - if read pass end of stream
      QueryException

    • read

      public List<Object> read(int number) throws DatabaseException
      PUBLIC: This method differs slightly from conventional read() operation on a Java stream. This method returns the next number of objects in the collection in a vector. Return the next object from the collection, if beyond the read limit read from the cursor
      Parameters:
      number - - number of objects to be returned
      Returns:
      - vector containing next number of objects
      Throws:
      DatabaseException - if read pass end of stream

    • clear

      public void clear()
      PUBLIC: Release all objects read in so far. This should be performed when reading in a large collection of objects in order to preserve memory.
      Overrides:
      clear in class Cursor

    • releasePrevious

      public void releasePrevious()
      PUBLIC: Release all objects read in so far. This should be performed when reading in a large collection of objects in order to preserve memory.

    • reset

      public void reset()
      PUBLIC: Repositions this stream to the position at the time the mark method was last called on this stream.

    • retrieveNextObject

      protected Object retrieveNextObject() throws DatabaseException
      Description copied from class: Cursor
      INTERNAL: Read the next row from the result set.
      Specified by:
      retrieveNextObject in class Cursor
      Throws:
      DatabaseException

    • retrieveNextPage

      protected Object retrieveNextPage() throws DatabaseException
      INTERNAL: Retrieve and add the next page size of rows to the vector. Return the last object, or null if at end.
      Throws:
      DatabaseException

    • setLimits

      protected void setLimits()
      INTERNAL: Initialize the stream size and position

    • setMarker

      protected void setMarker(int value)
      INTERNAL: Set the marker used for mark() & reset() operations