Package org.zalando.nakadiproducer.snapshots

Interface SnapshotEventGenerator

All Known Implementing Classes:

SimpleSnapshotEventGenerator

public interface SnapshotEventGenerator

The SnapshotEventGenerator interface should be implemented by any event producer that wants to support the snapshot events feature. The class must define a method generateSnapshots(java.lang.Object, java.lang.String), as well as getSupportedEventType(). The of(java.lang.String, java.util.function.Function<java.lang.Object, java.util.List<org.zalando.nakadiproducer.snapshots.Snapshot>>) methods can be used for creating an implementation from method references or lambdas:

{@code

Method Summary

Modifier and Type	Method	Description
List<Snapshot>	generateSnapshots(Object withIdGreaterThan, String filter)	Returns a batch of snapshots of given type (event type is an event channel topic name).
String	getSupportedEventType()	The name of the event type supported by this snapshot generator.
static SnapshotEventGenerator	of(String eventType, BiFunction<Object,String,List<Snapshot>> generator)	Creates a SnapshotEventGenerator for an event type, with filtering support.
static SnapshotEventGenerator	of(String eventType, Function<Object,List<Snapshot>> generator)	Creates a SnapshotEventGenerator for an event type, which doesn't support filtering.

Method Detail

generateSnapshots

List<Snapshot> generateSnapshots(@Nullable
                                 Object withIdGreaterThan,
                                 String filter)

Returns a batch of snapshots of given type (event type is an event channel topic name). The implementation may return an arbitrary amount of results, but it must return at least one element if there are entities matching the parameters.

Calling this method must have no side effects.

The library will call your implementation like this:

• Request: generateSnapshots(null, filter), Response: 1,2,3
• Request: generateSnapshots(3, filter), Response: 4,5
• Request: generateSnapshots(5, filter), Response: emptyList

It is your responsibility to make sure that the returned events are ordered by their ID ascending and that, given you return a list of events for entities with IDs {id₁, ..., id_N}, there exists no entity with an ID between id₁ and id_N, that is not part of the result.

Parameters:

withIdGreaterThan - if not null, only events for entities with an ID greater than the given one must be returned

filter - a filter for the snapshot generation mechanism. This value is simply passed through from the request body of the REST endpoint (or from any other triggering mechanism). If there was no request body, this will be null. Implementors can interpret it in whatever way they want (even ignore it). All calls for one snapshot generation will receive the same string.

Returns:

list of elements (wrapped in Snapshot objects) ordered by their ID.

getSupportedEventType

String getSupportedEventType()

The name of the event type supported by this snapshot generator.

of

static SnapshotEventGenerator of(String eventType,
                                 Function<Object,List<Snapshot>> generator)

Creates a SnapshotEventGenerator for an event type, which doesn't support filtering.

Parameters:

eventType - the eventType that this SnapShotEventProvider will support.

generator - a snapshot event factory function conforming to the specification of generateSnapshots(Object, String) (but without the filter parameter). Any filter provided by the caller will be thrown away.

Since:

21.1.0

of

static SnapshotEventGenerator of(String eventType,
                                 BiFunction<Object,String,List<Snapshot>> generator)

Creates a SnapshotEventGenerator for an event type, with filtering support.

Parameters:

eventType - the eventType that this SnapShotEventProvider will support.

generator - a snapshot event factory function conforming to the specification of generateSnapshots(Object, String).

Since:

21.1.0