org.eclipse.persistence.queries
Class CursoredStream

java.lang.Object
  org.eclipse.persistence.queries.Cursor
      org.eclipse.persistence.queries.CursoredStream

All Implemented Interfaces:

java.io.Serializable, java.util.Enumeration, java.util.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:

Serialized Form

Author:

Yvon Lavoie

Since:

TOPLink/Java 1.0

Field Summary

protected int

marker Marker for backing up.

Fields inherited from class org.eclipse.persistence.queries.Cursor

executionSession, fields, initiallyConformingIndex, nextRow, objectCollection, policy, position, query, resultSet, selectionCriteriaClone, session, size, statement, translationRow

Constructor Summary

CursoredStream()
INTERNAL: Initialize the state of the stream

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

Method Summary

boolean	atEnd() PUBLIC: Return whether the cursored stream is at its end.
int	available() PUBLIC: Returns the number of objects that can be read from this input without blocking.
Expression	buildCountDistinctExpression(java.util.List includeFields, ExpressionBuilder builder) INTERNAL: Must build the count on the primary key fields, not * as * is not allowed if there was a distinct.
void	clear() PUBLIC: Release all objects read in so far.
protected java.util.List<java.lang.Object>	copy(int startIndex, int endIndex) INTERNAL: Answer a list of the elements of the receiver's collection from startIndex to endIndex.
protected int	getCursorSize() INTERNAL: Retrieve the size of the open cursor by executing a count on the same query as the cursor.
protected int	getInitialReadSize() INTERNAL: Return the threshold for the stream.
protected int	getMarker() INTERNAL: Return the marker used for mark() & reset() operations.
int	getPageSize() INTERNAL: Return the page size for the stream.
int	getPosition() INTERNAL: Return the position of the stream inside the object collection
boolean	hasMoreElements() PUBLIC: Return whether the cursored stream has any more elements.
boolean	hasNext() PUBLIC: Return whether the cursored stream has any more elements.
void	mark(int readAheadLimit) PUBLIC: Mark the present position in the stream.
boolean	markSupported() PUBLIC: Tests if this input stream supports the mark and reset methods.
java.lang.Object	next() PUBLIC: Return the next object from the collection, if beyond the read limit read from the cursor.
java.util.List<java.lang.Object>	next(int numberOfElements) PUBLIC: Return a Vector of at most numberOfElements of the next objects from the collection.
java.lang.Object	nextElement() PUBLIC: Return the next object from the collection, if beyond the read limit read from the cursor.
java.util.Vector	nextElements(int numberOfElements) PUBLIC: Return a Vector of at most numberOfElements of the next objects from the collection.
java.lang.Object	peek() PUBLIC: Return the next object in the stream, without incrementing the stream's position.
java.lang.Object	read() PUBLIC: This method differs slightly from conventional read() operation on a Java stream.
java.util.List<java.lang.Object>	read(int number) PUBLIC: This method differs slightly from conventional read() operation on a Java stream.
void	releasePrevious() PUBLIC: Release all objects read in so far.
void	reset() PUBLIC: Repositions this stream to the position at the time the mark method was last called on this stream.
protected java.lang.Object	retrieveNextObject() INTERNAL: Read the next row from the result set.
protected java.lang.Object	retrieveNextPage() INTERNAL: Retrieve and add the next page size of rows to the vector.
protected void	setLimits() INTERNAL: Initialize the stream size and position
protected void	setMarker(int value) INTERNAL: Set the marker used for mark() & reset() operations

Methods inherited from class org.eclipse.persistence.queries.Cursor

buildAndRegisterObject, close, finalize, getAccessor, getExecutionSession, getFields, getInitiallyConformingIndex, getObjectCollection, getPolicy, getQuery, getResultSet, getSelectionCriteriaClone, getSession, getStatement, getTranslationRow, isClosed, remove, setExecutionSession, setFields, setInitiallyConformingIndex, setObjectCollection, setPolicy, setPosition, setResultSet, setSelectionCriteriaClone, setSession, setSize, setTranslationRow, size

Methods inherited from class java.lang.Object

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

Field Detail

marker

protected int marker

Marker for backing up.

Constructor Detail

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 Detail

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(java.util.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 java.util.List<java.lang.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 java.lang.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 java.lang.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 java.util.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 java.util.List<java.lang.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 java.lang.Object peek()
                      throws DatabaseException

PUBLIC: Return the next object in the stream, without incrementing the stream's position.

Throws:

DatabaseException

read

public java.lang.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:

- - throws exception if read pass end of stream

DatabaseException

QueryException

read

public java.util.List<java.lang.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:

- - throws exception if read pass end of stream

DatabaseException

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 java.lang.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 java.lang.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