com.infoscape.proteus
Class PolledSource

java.lang.Object
  |
  +--com.infoscape.proteus.MessageHandlerImpl
        |
        +--com.infoscape.proteus.SourceImpl
              |
              +--com.infoscape.proteus.PolledSource

All Implemented Interfaces:

MessageHandler, MessageSource, Transactional

Direct Known Subclasses:

DBSource, FTPSource

public abstract class PolledSource

extends SourceImpl

Base class for polled sources. A lot of potential message sources are not, in and of themselves, event sources. Database tables, remote FTP servers, and directories in the local filesystem all come to mind. To treat these as event sources you need to listen to them actively. At regular intervals, you need to inquire whether there are any messages there and grab them if the answer is yes. Typically grabbing messages is an operation that returns more than one message, so you need to store the extra messages in some sort of cache and return them one by one in response to a call to getMessage(). PolledSource encapsulates these common features. A PolledSource is initialized with a pollPeriod, an integer value (in seconds) which defaults to 60. Descendants of PolledSource do not implement getMessage() (or even _getMessage()) directly. Instead they implement three methods: cacheEmpty(), loadCache() and getFromCache().

Field Summary

protected int

pollPeriod

Constructor Summary

PolledSource(Connection conn, org.jdom.Element elt)

Method Summary

protected java.lang.Object	_getMessage()
abstract boolean	cacheEmpty()
abstract java.lang.Object	getFromCache()
abstract void	loadCache()

Methods inherited from class com.infoscape.proteus.SourceImpl

getMessage

Methods inherited from class com.infoscape.proteus.MessageHandlerImpl

commit, disconnect, getConnection, log, log, reconnect, rollback, setSyncPoint

Methods inherited from class java.lang.Object

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

Methods inherited from interface com.infoscape.proteus.MessageHandler

disconnect, getConnection, reconnect

Methods inherited from interface com.infoscape.proteus.Transactional

commit, rollback, setSyncPoint

Field Detail

pollPeriod

protected int pollPeriod

Constructor Detail

PolledSource

public PolledSource(Connection conn,
                    org.jdom.Element elt)
             throws java.lang.Exception

Parameters:

conn -

elt -

Throws:

java.lang.Exception

Method Detail

_getMessage

protected java.lang.Object _getMessage()
                                throws java.lang.Exception

Specified by:

_getMessage in class SourceImpl

Throws:

java.lang.Exception

cacheEmpty

public abstract boolean cacheEmpty()
                            throws java.lang.Exception

java.lang.Exception

loadCache

public abstract void loadCache()
                        throws java.lang.Exception

java.lang.Exception

getFromCache

public abstract java.lang.Object getFromCache()
                                       throws java.lang.Exception

java.lang.Exception