org.sape.carbon.services.uniqueid
Class DefaultUniqueIDServiceImpl

java.lang.Object
  |
  +--org.sape.carbon.services.uniqueid.DefaultUniqueIDServiceImpl

All Implemented Interfaces:

Configurable, FunctionalInterface, UniqueIDService

public class DefaultUniqueIDServiceImpl

extends Object

implements UniqueIDService, Configurable

Default implementation of UniqueIDService interface. This implementation uses a database to store the next unique id. It uses transactions at the database level to ensure ID uniqueness across a cluster of machines and synchronization to ensure that this component does not return the same ID twice. To decrease database hits, this implementation stores a block of IDs with each database request instead of querying the database for each ID. Copyright 2002 Sapient

Since:

carbon 1.0

Version:

$Revision: 1.12 $($Author: dvoet $ / $Date: 2003/05/05 21:21:38 $)

Author:

Vivekanand Kirubanandan, June 2002

Field Summary

protected boolean	autoCreate Enable/disable autocreate if the id doesnt exist
protected long	blockSize The number of IDs reserved with each database request
protected ConnectionFactory	connectionFactory Connection Factory used for the Select/Update query
protected String	createStatementName Name of of the create statement within statementFactory
protected long	currentBlockEnd End value of the current block (inclusive)
protected long	currentBlockStart Start value of the current block (inclusive)
protected long	currentValue Current value of the ID, returned by the next call to getNextID
protected String	idName UniqueID name used to identify the ID in the database
protected long	initialBlockStart Starting value of the ID used while creating a new id
private boolean	isSecondAttemptRequired This variable is used to ensure that only one attempt is made to retreive a new block of unique id in case of synchronization problem when two threads are trying to create the same unique id name at the same time.
private org.apache.commons.logging.Log	log Provides a handle to Apache-commons logger
protected boolean	retrieveNewBlock Flag that signifies that a new ID block should be retrieved regardless of currentValue and whether it falls outside of the current block.
protected String	retrieveStatementName Name of of the retrieve statement within statementFactory
protected StatementFactory	statementFactory Factory used to get the Statements to query the database
protected String	updateStatementName Name of of the update statement within statementFactory

Constructor Summary

DefaultUniqueIDServiceImpl()

Method Summary

void	configure(ComponentConfiguration configuration) Configure the component.
protected long	createUniqueID() Inserts a new row into the Unique ID holding table with an initial value defined by initialBlockStart which is set from configuration.
long	getNextID() Method is expected to return then next value, if the value is in the current block, otherwise resever a new block.
protected void	reserveBlock(long nextBlockStart, Connection connection) Reserves a block of IDs by updating the row corresponding to this ID, increasing it by blockSize (configurable).
protected void	reserveNewBlock() Reserves a new block of IDs, creating it if it does not exists and this component is configured to do so.
protected long	retrieveBlockStart(Connection connection) Retrieves the beginning of the next block of IDs.

Methods inherited from class java.lang.Object

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

Field Detail

log

private org.apache.commons.logging.Log log

Provides a handle to Apache-commons logger

idName

protected String idName

UniqueID name used to identify the ID in the database

blockSize

protected long blockSize

The number of IDs reserved with each database request

initialBlockStart

protected long initialBlockStart

Starting value of the ID used while creating a new id

currentBlockStart

protected long currentBlockStart

Start value of the current block (inclusive)

currentBlockEnd

protected long currentBlockEnd

End value of the current block (inclusive)

currentValue

protected long currentValue

Current value of the ID, returned by the next call to getNextID

autoCreate

protected boolean autoCreate

Enable/disable autocreate if the id doesnt exist

statementFactory

protected StatementFactory statementFactory

Factory used to get the Statements to query the database

connectionFactory

protected ConnectionFactory connectionFactory

Connection Factory used for the Select/Update query

retrieveStatementName

protected String retrieveStatementName

Name of of the retrieve statement within statementFactory

updateStatementName

protected String updateStatementName

Name of of the update statement within statementFactory

createStatementName

protected String createStatementName

Name of of the create statement within statementFactory

retrieveNewBlock

protected boolean retrieveNewBlock

Flag that signifies that a new ID block should be retrieved regardless of currentValue and whether it falls outside of the current block. Set to true by the configuration method and to false by the getNextID method after it gets a new block.

isSecondAttemptRequired

private boolean isSecondAttemptRequired

This variable is used to ensure that only one attempt is made to retreive a new block of unique id in case of synchronization problem when two threads are trying to create the same unique id name at the same time.

true : indicates only one attempt has been made and second is required
false : indicates, no more attempts are required, continue the execution

Constructor Detail

DefaultUniqueIDServiceImpl

public DefaultUniqueIDServiceImpl()

Method Detail

getNextID

public long getNextID()
               throws UniqueIDServiceException

Method is expected to return then next value, if the value is in the current block, otherwise resever a new block.

Specified by:

getNextID in interface UniqueIDService

Returns:

the next unique id

Throws:

UniqueIDServiceException - if unable to generate the value

configure

public void configure(ComponentConfiguration configuration)

Configure the component. Uses the UniqueIDServiceConfiguration

Specified by:

configure in interface Configurable

Parameters:

configuration - A UniqueIDServiceConfiguration

See Also:

UniqueIDServiceConfiguration

reserveNewBlock

protected void reserveNewBlock()
                        throws UniqueIDServiceException

Reserves a new block of IDs, creating it if it does not exists and this component is configured to do so. Transactions are handled at this level to ensure only one component gets a new block at a time for this ID.

Throws:

UniqueIDServiceException - indicates an generic error

retrieveBlockStart

protected long retrieveBlockStart(Connection connection)
                           throws UniqueIDNotFoundException,
                                  UniqueIDServiceException

Retrieves the beginning of the next block of IDs.

Parameters:

connection - connection used to query the database, explicitly passed to allow transaction handling

Returns:

long the current value

Throws:

UniqueIDNotFoundException - indicates the ID is not found

UniqueIDServiceException - indicates a generic error

reserveBlock

protected void reserveBlock(long nextBlockStart,
                            Connection connection)
                     throws UniqueIDServiceException

Reserves a block of IDs by updating the row corresponding to this ID, increasing it by blockSize (configurable).

Parameters:

nextBlockStart - the starting value of the next block of IDs

connection - the connection used to update the database, explicitly passed to allow transaction handling

Throws:

UniqueIDServiceException - indicates an error reserving a block

createUniqueID

protected long createUniqueID()
                       throws UniqueIDCreationException,
                              SQLException

Inserts a new row into the Unique ID holding table with an initial value defined by initialBlockStart which is set from configuration. This Unique ID can then be accessed through the normal reserveBlock method.

Returns:

long the current value of the ID in the table

Throws:

UniqueIDCreationException - when unable to create the Unique ID in the table

SQLException - when unable to insert the row in table