com.antelmann.db
Class SessionIdGenerator

java.lang.Object
  com.antelmann.db.SessionIdGenerator

All Implemented Interfaces:

IDFactory, Converter<Integer,String>

Direct Known Subclasses:

GIDFactory

public abstract class SessionIdGenerator
extends Object
implements IDFactory, Converter<Integer,String>

This class provides efficient unique String-based IDs for different clients. The implementation uses one abstract method to generate (and store) an ID for a client session. This session-ID is then used as a prefix for the actual IDs that are given out by the method generateNewID(), which is to be used to create new IDs from this class. Each ID given out is unique, as the ID concatenates the session-prefix with a counter, that is incremented on each call. This way, this implementation creates new IDs quite efficiently, as a call to the database only needs to occur once for the initialization of the prefix. After initialization, every call to generate a new ID for the client only requires local access of this class where a simple counter is used to guarantee that each call for generating a new ID is unique.

Since:

27. August 2007, 21:56

Author:

Holger Antelmann

See Also:

DBClassStore.generateNewID()

Nested Class Summary

Nested classes/interfaces inherited from interface com.antelmann.util.Converter

Converter.Adapter<T1,T2>

Constructor Summary

SessionIdGenerator(Database<?> db)

SessionIdGenerator(Database<?> db, int radix)
before any IDs can be retrieved, the instance must be initialized before use.

Method Summary

String	convert(Integer i)
Integer	convertBack(String str)
String	generateNewID()
Object	generateNewID(Class<? extends DBEntry> entryClass) this implementation doesn't do anything but returning generateNewID(), thus disregarding the given parameter
protected abstract String	generateSessionPrefix() this method is to access the database to generate a new session prefix on every call and also store it into the database, so that it is guaranteed that no other call ever re-uses this prefix again.
protected String	generateSQLSessionPrefix(Connection con, String table, String idColumn, String sessionKey, String valueColumn, String separator)
int	getCounter() returns the current value of the session counter
Database<?>	getDatabase()
int	getRadix() unless changed, the default value is 10.
String	getSessionPrefix() returns the prefix for the current session; if this instance is not initialized, this method return s null;
void	initNewSession() this method must be called at least once after instanciation to init a new session for providing unique IDs.
void	setRadix(int radix) allows to adjust the radix for generating the number string to compress the length of a generated ID.
void	setSessionDataManually(String sessionPrefix, int counter, boolean yesIKnowWhatIAmDoing) allows to manually override the session prefix - use with caution - if at all

Methods inherited from class java.lang.Object

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

Constructor Detail

SessionIdGenerator

public SessionIdGenerator(Database<?> db)

SessionIdGenerator

public SessionIdGenerator(Database<?> db,
                          int radix)

before any IDs can be retrieved, the instance must be initialized before use.

See Also:

initNewSession()

Method Detail

getRadix

public int getRadix()

unless changed, the default value is 10.

See Also:

setRadix(int)

setRadix

public void setRadix(int radix)

allows to adjust the radix for generating the number string to compress the length of a generated ID.

See Also:

Integer.toString(int, int)

generateSessionPrefix

protected abstract String generateSessionPrefix()
                                         throws DatabaseException

this method is to access the database to generate a new session prefix on every call and also store it into the database, so that it is guaranteed that no other call ever re-uses this prefix again. Note that this method must not manage the transaction, as this method is called by initNewSession(), which begins and commits its own transaction; i.e. this method can be savely assumed to run within a synchronized transaction.

Returns:

a new unique session-ID from the database to be used as a prefix for this session

Throws:

DatabaseException

See Also:

initNewSession()

setSessionDataManually

@Warning(value="using this method may result in non-unique IDs - YOU BETTER KNOW WHAT YOU\'RE DOING HERE")
public void setSessionDataManually(String sessionPrefix,
                                                int counter,
                                                boolean yesIKnowWhatIAmDoing)

allows to manually override the session prefix - use with caution - if at all

initNewSession

public void initNewSession()
                    throws DatabaseException

this method must be called at least once after instanciation to init a new session for providing unique IDs. On each call, this method (synchronized on the transaction object) begins a transaction, calls generateSessionPrefix() and then commits the transaction, so that it is guaranteed that every call from any client at any time will initialize a new and unique session.

Throws:

DatabaseException

See Also:

generateSessionPrefix()

getSessionPrefix

public String getSessionPrefix()

returns the prefix for the current session; if this instance is not initialized, this method return s null;

getCounter

public int getCounter()

returns the current value of the session counter

generateNewID

public Object generateNewID(Class<? extends DBEntry> entryClass)
                     throws DatabaseException,
                            IllegalArgumentException

this implementation doesn't do anything but returning generateNewID(), thus disregarding the given parameter

Specified by:

generateNewID in interface IDFactory

Returns:

an Object for use as an ID for the given DBEntry class.

Throws:

DatabaseException

IllegalArgumentException

convert

public String convert(Integer i)

Specified by:

convert in interface Converter<Integer,String>

convertBack

public Integer convertBack(String str)
                    throws IllegalArgumentException

Specified by:

convertBack in interface Converter<Integer,String>

Throws:

IllegalArgumentException

generateNewID

public String generateNewID()
                     throws IllegalStateException

Returns:

a unique ID on every call that can be used as a String-based ID for DBEntry objects.

Throws:

IllegalStateException - if no session has been initialized, yet

See Also:

initNewSession(), DBEntry, DBClassStore.generateNewID()

getDatabase

public Database<?> getDatabase()

generateSQLSessionPrefix

protected String generateSQLSessionPrefix(Connection con,
                                          String table,
                                          String idColumn,
                                          String sessionKey,
                                          String valueColumn,
                                          String separator)
                                   throws DatabaseException

Throws:

DatabaseException