org.dasein.persist
Class Sequencer

java.lang.Object
  org.dasein.persist.Sequencer

Direct Known Subclasses:

DaseinSequencer

public abstract class Sequencer
extends Object

Provides a generic interface for sequence generation that may be implemented by a number of different sequence providers. You request sequencer instances by calling getInstance(String) with the name of the sequence or getInstance(Class) with the class for which the sequence should be unique. You may configure what sequencer is used through the configuration file dasein-persistence.properties. You specify a concrete sequencer using the following:
dasein.sequencer.NAME=CLASSNAME

For example:
dasein.sequencer.pageId=org.dasein.persist.DaseinSequencer

In code, you might have the following:

Sequencer seq = Sequencer.getInstance(this.class);
id = seq.next();

Last modified $Date: 2005/08/15 16:15:59 $

Version:

$Revision: 1.2 $

Author:

George Reese

Field Summary

static String

PROPERTIES

Constructor Summary

Sequencer()
Constructs an empty sequencer with no name.

Method Summary

static Sequencer	getInstance(Class cls) Returns a sequencer that will provide unique identifiers across all instances of the specified class.
static Sequencer	getInstance(String name) Looks to see if a sequencer has been generated for the sequence with the specified name.
String	getName()
abstract long	next() Generates a new unique number based on the implementation class' algorithm of choice.
void	setName(String nom) Sets the sequencer name.

Methods inherited from class java.lang.Object

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

Field Detail

PROPERTIES

public static final String PROPERTIES

See Also:

Constant Field Values

Constructor Detail

Sequencer

public Sequencer()

Constructs an empty sequencer with no name. This constructor should be followed by a call to setName(String) before the sequencer is used.

Method Detail

getInstance

public static final Sequencer getInstance(String name)

Looks to see if a sequencer has been generated for the sequence with the specified name. If not, it will instantiate one. Multiple calls to this method with the same name are guaranteed to receive the same sequencer object. For best performance, classes should save a reference to the sequencer once they get it in order to avoid the overhead of a HashMap lookup.

Parameters:

name - the name of the desired sequencer

Returns:

the sequencer with the specified name

getInstance

public static Sequencer getInstance(Class cls)

Returns a sequencer that will provide unique identifiers across all instances of the specified class. This method is simply a convenience method for calling getInstance(String) where the name being used for the desired sequence is the name of the class passed to this method.

Parameters:

cls - the class for which unique IDs are desired

Returns:

a sequencer that generates unique IDs for the specified class

getName

public String getName()

Returns:

the name of the sequencer

next

public abstract long next()
                   throws PersistenceException

Generates a new unique number based on the implementation class' algorithm of choice. The generated number must be a Java long that is guaranteed to be unique for all sequences sharing this name.

Returns:

a unique number for the sequence of this sequencer's name

Throws:

PersistenceException - a data store error occurred while generating the number

setName

public final void setName(String nom)

Sets the sequencer name.

Parameters:

nom - the name of the sequencer