org.apache.fluo.api.observer

Interface Observer

All Known Implementing Classes:

AbstractObserver

public interface Observer

Implemented by users to a watch a Column and be notified of changes to the Column via the process(TransactionBase, Bytes, Column) method. An observer is created for each worker thread and reused for the lifetime of a worker thread. Consider extending AbstractObserver as it will let you optionally implement init(Context) and close(). The abstract class will also shield you from the addition of interface methods.

Since:

1.0.0

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static interface	Observer.Context
static class	Observer.NotificationType
static class	Observer.ObservedColumn A Column and Observer.NotificationType pair

Method Summary

Modifier and Type	Method and Description
void	close() Implemented by user to close resources used by Observer
Observer.ObservedColumn	getObservedColumn() Implemented by user to return an Observer.ObservedColumn that will trigger this observer.
void	init(Observer.Context context) Implemented by user to initialize Observer.
void	process(TransactionBase tx, Bytes row, Column col) Implemented by users to process notifications on a Observer.ObservedColumn.

Method Detail

init

void init(Observer.Context context)
   throws Exception

Implemented by user to initialize Observer.

Parameters:

context - Observer context

Throws:

Exception

process

void process(TransactionBase tx,
             Bytes row,
             Column col)
      throws Exception

Implemented by users to process notifications on a Observer.ObservedColumn. If a notification occurs, this method passes the user a TransactionBase as well as the row and Column where the notification occurred. The user can use the TransactionBase to read and write to Fluo. After this method returns, TransactionBase will be committed and closed by Fluo.

Throws:

Exception

getObservedColumn

Observer.ObservedColumn getObservedColumn()

Implemented by user to return an Observer.ObservedColumn that will trigger this observer. During initialization, this information is stored in zookeeper so that workers have a consistent view. If a worker loads an Observer and the information returned differs from what is in zookeeper then an exception will be thrown. It is safe to assume that init(Context) will be called before this method. If the return value of the method is derived from what is passed to init(Context), then the derivation process should be deterministic.

close

void close()

Implemented by user to close resources used by Observer