com.lightbend.lagom.javadsl.projection

Interface Projections

All Known Implementing Classes:

ProjectionsImpl

@ApiMayChange
public interface Projections

Public interface to query the internal projection registry that keeps track of the State of each projection. A projections is a process consuming an Akka Persistence Journal handling each event into a read table or a broker topic. In Lagom the term projection only refers to ReadSideProcessor's and TopicProducers's (not Broker subscribers). This is different than the meaning of projection in akka/akka-projection.

See also https://www.lagomframework.com/documentation/latest/java/Projections.html

Method Summary

Modifier and Type	Method and Description
CompletionStage<State>	getStatus() Read an eventually consistent copy of the projections and workers running on the service.
void	startAllWorkers(String projectionName) Given a `projectionName`, request all its workers to start.
void	startWorker(String projectionName, String tagName) Given a `projectionName` and a `tagName` request a single worker to start.
void	stopAllWorkers(String projectionName) Given a `projectionName`, request all its workers to stop.
void	stopWorker(String projectionName, String tagName) Given a `projectionName` and a `tagName` request a single worker to stop.

Method Detail

getStatus

CompletionStage<State> getStatus()

Read an eventually consistent copy of the projections and workers running on the service. Invocations to this method return a local copy of the `State` so multiple invocations in different nodes of the cluster may return different versions of `State` when it is evolving (e.g. during a rolling upgrade, while attending a user request to stop/start,...)

Returns:

an eventually consistent list of projections' metadata

stopAllWorkers

void stopAllWorkers(String projectionName)

Given a `projectionName`, request all its workers to stop. This method returns immediately. Eventually, the request will propagate across the cluster and, after that, workers participating on that projection will stop. To track the actual state of the workers, poll the projection registry using the method `getStatus`.

stopWorker

void stopWorker(String projectionName,
                String tagName)

Given a `projectionName` and a `tagName` request a single worker to stop. This method returns immediately. Eventually, the request will propagate across the cluster and reach the node where that particular worker is currently allocated. Then, the worker will be stopped, it's status change will be observed and propagated back across the cluster. To track the actual state of the workers, poll the projection registry using the method `getStatus`.

startAllWorkers

void startAllWorkers(String projectionName)

Given a `projectionName`, request all its workers to start. This method returns immediately. Eventually, the request will propagate across the cluster and, after that, workers participating on that projection will start. To track the actual state of the workers, poll the projection registry using the method `getStatus`.

startWorker

void startWorker(String projectionName,
                 String tagName)

Given a `projectionName` and a `tagName` request a single worker to start. This method returns immediately. Eventually, the request will propagate across the cluster and reach the node where that particular worker must be allocated allocated. Then, the worker will be started, it's status change will be observed and propagated back across the cluster. To track the actual state of the workers, poll the projection registry using the method `getStatus`.