org.axonframework.queryhandling

Class SimpleQueryBus

java.lang.Object

org.axonframework.queryhandling.SimpleQueryBus

All Implemented Interfaces:

MessageDispatchInterceptorSupport<QueryMessage<?,?>>, MessageHandlerInterceptorSupport<QueryMessage<?,?>>, QueryBus

public class SimpleQueryBus
extends Object
implements QueryBus

Implementation of the QueryBus that dispatches queries to the handlers within the JVM. Any timeouts are ignored by this implementation, as handlers are considered to answer immediately.

In case multiple handlers are registered for the same query and response type, the query(QueryMessage) method will invoke one of these handlers. Which one is unspecified.

Since:

3.1

Author:

Marc Gathier, Allard Buijze, Steven van Beelen, Milan Savic

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	SimpleQueryBus.Builder Builder class to instantiate a SimpleQueryBus.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	SimpleQueryBus(SimpleQueryBus.Builder builder) Instantiate a SimpleQueryBus based on the fields contained in the SimpleQueryBus.Builder.

Method Summary

Modifier and Type	Method and Description
static SimpleQueryBus.Builder	builder() Instantiate a Builder to be able to create a SimpleQueryBus.
protected Map<String,Collection<QuerySubscription<?>>>	getSubscriptions() Returns the subscriptions for this query bus.
<Q,R> CompletableFuture<QueryResponseMessage<R>>	query(QueryMessage<Q,R> query) Dispatch the given query to a single QueryHandler subscribed to the given query's queryName and responseType.
QueryUpdateEmitter	queryUpdateEmitter() Gets the QueryUpdateEmitter associated with this QueryBus.
Registration	registerDispatchInterceptor(MessageDispatchInterceptor<? super QueryMessage<?,?>> interceptor) Registers an interceptor that intercepts Queries as they are sent.
Registration	registerHandlerInterceptor(MessageHandlerInterceptor<? super QueryMessage<?,?>> interceptor) Registers an interceptor that is used to intercept Queries before they are passed to their respective handlers.
<Q,R> Stream<QueryResponseMessage<R>>	scatterGather(QueryMessage<Q,R> query, long timeout, TimeUnit unit) Dispatch the given query to all QueryHandlers subscribed to the given query's queryName/responseType.
<Q,R> org.reactivestreams.Publisher<QueryResponseMessage<R>>	streamingQuery(StreamingQueryMessage<Q,R> query) Builds a Publisher of responses to the given query.
<R> Registration	subscribe(String queryName, Type responseType, MessageHandler<? super QueryMessage<?,R>> handler) Subscribe the given handler to queries with the given queryName and responseType.
<Q,I,U> SubscriptionQueryResult<QueryResponseMessage<I>,SubscriptionQueryUpdateMessage<U>>	subscriptionQuery(SubscriptionQueryMessage<Q,I,U> query, int updateBufferSize) Dispatch the given query to a single QueryHandler subscribed to the given query's queryName/initialResponseType/updateResponseType.
<Q,I,U> SubscriptionQueryResult<QueryResponseMessage<I>,SubscriptionQueryUpdateMessage<U>>	subscriptionQuery(SubscriptionQueryMessage<Q,I,U> query, SubscriptionQueryBackpressure backpressure, int updateBufferSize) Deprecated. in favor use of {subscriptionQuery(SubscriptionQueryMessage, int)

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.axonframework.queryhandling.QueryBus

subscriptionQuery

Constructor Detail

SimpleQueryBus

protected SimpleQueryBus(SimpleQueryBus.Builder builder)

Instantiate a SimpleQueryBus based on the fields contained in the SimpleQueryBus.Builder.

Parameters:

builder - the SimpleQueryBus.Builder used to instantiate a SimpleQueryBus instance

Method Detail

builder

public static SimpleQueryBus.Builder builder()

Instantiate a Builder to be able to create a SimpleQueryBus.

The MessageMonitor is defaulted to NoOpMessageMonitor, TransactionManager to NoTransactionManager, QueryInvocationErrorHandler to LoggingQueryInvocationErrorHandler, the QueryBusSpanFactory defaults to a DefaultQueryBusSpanFactory backed by a NoOpSpanFactory and QueryUpdateEmitter to SimpleQueryUpdateEmitter.

Returns:

a Builder to be able to create a SimpleQueryBus

subscribe

public <R> Registration subscribe(@Nonnull
                                  String queryName,
                                  @Nonnull
                                  Type responseType,
                                  @Nonnull
                                  MessageHandler<? super QueryMessage<?,R>> handler)

Description copied from interface: QueryBus

Subscribe the given handler to queries with the given queryName and responseType. Multiple handlers may subscribe to the same combination of queryName/responseType.

Specified by:

subscribe in interface QueryBus

Parameters:

queryName - the name of the query request to subscribe

responseType - the type of response the subscribed component answers with

handler - a handler that implements the query

Returns:

a handle to un-subscribe the query handler

query

public <Q,R> CompletableFuture<QueryResponseMessage<R>> query(@Nonnull
                                                              QueryMessage<Q,R> query)

Description copied from interface: QueryBus

Dispatch the given query to a single QueryHandler subscribed to the given query's queryName and responseType. This method returns all values returned by the Query Handler as a Collection. This may or may not be the exact collection as defined in the Query Handler.

If the Query Handler defines a single return object (i.e. not a collection or array), that object is returned as the sole entry in a singleton collection.

When no handlers are available that can answer the given query, the returned CompletableFuture will be completed with a NoHandlerForQueryException.

Specified by:

query in interface QueryBus

Type Parameters:

Q - the payload type of the query

R - the response type of the query

Parameters:

query - the query

Returns:

a CompletableFuture that resolves when the response is available

streamingQuery

public <Q,R> org.reactivestreams.Publisher<QueryResponseMessage<R>> streamingQuery(StreamingQueryMessage<Q,R> query)

Description copied from interface: QueryBus

Builds a Publisher of responses to the given query. The actual query is not dispatched until there is a subscription to the result. The query is dispatched to a single query handler. Implementations may opt for invoking several query handlers and then choosing a response from single one for performance or resilience reasons.

When no handlers are available that can answer the given query, the return Publisher will be completed with a NoHandlerForQueryException.

Specified by:

streamingQuery in interface QueryBus

Type Parameters:

Q - the payload type of the streaming query

R - the response type of the streaming query

Parameters:

query - the streaming query message

Returns:

a Publisher of responses

scatterGather

public <Q,R> Stream<QueryResponseMessage<R>> scatterGather(@Nonnull
                                                           QueryMessage<Q,R> query,
                                                           long timeout,
                                                           @Nonnull
                                                           TimeUnit unit)

Description copied from interface: QueryBus

Dispatch the given query to all QueryHandlers subscribed to the given query's queryName/responseType. Returns a stream of results which blocks until all handlers have processed the request or when the timeout occurs.

If no handlers are available to provide a result, or when all available handlers throw an exception while attempting to do so, the returned Stream is empty.

Note that any terminal operation (such as Stream.forEach(Consumer)) on the Stream may cause it to block until the timeout has expired, awaiting additional data to include in the stream.

Specified by:

scatterGather in interface QueryBus

Type Parameters:

Q - the payload type of the query

R - the response type of the query

Parameters:

query - the query

timeout - time to wait for results

unit - unit for the timeout

Returns:

stream of query results

subscriptionQuery

@Deprecated
public <Q,I,U> SubscriptionQueryResult<QueryResponseMessage<I>,SubscriptionQueryUpdateMessage<U>> subscriptionQuery(@Nonnull
                                                                                                                                SubscriptionQueryMessage<Q,I,U> query,
                                                                                                                                SubscriptionQueryBackpressure backpressure,
                                                                                                                                int updateBufferSize)

Deprecated. in favor use of {subscriptionQuery(SubscriptionQueryMessage, int)

Dispatch the given query to a single QueryHandler subscribed to the given query's queryName/initialResponseType/updateResponseType. The result is lazily created and there will be no execution of the query handler before there is a subscription to the initial result. In order not to miss updates, the query bus will queue all updates which happen after the subscription query is done and once the subscription to the flux is made, these updates will be emitted.

If there is an error during retrieving or consuming initial result, stream for incremental updates is NOT interrupted.

If there is an error during emitting an update, subscription is cancelled causing further emits not reaching the destination.

Provided backpressure mechanism will be used to deal with fast emitters.

Specified by:

subscriptionQuery in interface QueryBus

Type Parameters:

Q - the payload type of the query

I - the response type of the query

U - the incremental response types of the query

Parameters:

query - the query

backpressure - the backpressure mechanism to be used for emitting updates

updateBufferSize - the size of buffer which accumulates updates before subscription to the flux is made

Returns:

query result containing initial result and incremental updates

subscriptionQuery

public <Q,I,U> SubscriptionQueryResult<QueryResponseMessage<I>,SubscriptionQueryUpdateMessage<U>> subscriptionQuery(@Nonnull
                                                                                                                    SubscriptionQueryMessage<Q,I,U> query,
                                                                                                                    int updateBufferSize)

Description copied from interface: QueryBus

Dispatch the given query to a single QueryHandler subscribed to the given query's queryName/initialResponseType/updateResponseType. The result is lazily created and there will be no execution of the query handler before there is a subscription to the initial result. In order not to miss updates, the query bus will queue all updates which happen after the subscription query is done and once the subscription to the flux is made, these updates will be emitted.

If there is an error during retrieving or consuming initial result, stream for incremental updates is NOT interrupted.

If there is an error during emitting an update, subscription is cancelled causing further emits not reaching the destination.

Specified by:

subscriptionQuery in interface QueryBus

Type Parameters:

Q - the payload type of the query

I - the response type of the query

U - the incremental response types of the query

Parameters:

query - the query

updateBufferSize - the size of buffer which accumulates updates before subscription to the flux is made

Returns:

query result containing initial result and incremental updates

queryUpdateEmitter

public QueryUpdateEmitter queryUpdateEmitter()

Description copied from interface: QueryBus

Gets the QueryUpdateEmitter associated with this QueryBus.

Specified by:

queryUpdateEmitter in interface QueryBus

Returns:

the associated QueryUpdateEmitter

getSubscriptions

protected Map<String,Collection<QuerySubscription<?>>> getSubscriptions()

Returns the subscriptions for this query bus. While the returned map is unmodifiable, it may or may not reflect changes made to the subscriptions after the call was made.

Returns:

the subscriptions for this query bus

registerHandlerInterceptor

public Registration registerHandlerInterceptor(@Nonnull
                                               MessageHandlerInterceptor<? super QueryMessage<?,?>> interceptor)

Registers an interceptor that is used to intercept Queries before they are passed to their respective handlers. The interceptor is invoked separately for each handler instance (in a separate unit of work).

Specified by:

registerHandlerInterceptor in interface MessageHandlerInterceptorSupport<QueryMessage<?,?>>

Parameters:

interceptor - the interceptor to invoke before passing a Query to the handler

Returns:

handle to deregister the interceptor

registerDispatchInterceptor

@Nonnull
public Registration registerDispatchInterceptor(@Nonnull
                                                         MessageDispatchInterceptor<? super QueryMessage<?,?>> interceptor)

Registers an interceptor that intercepts Queries as they are sent. Each interceptor is called once, regardless of the type of query (point-to-point or scatter-gather) executed.

Specified by:

registerDispatchInterceptor in interface MessageDispatchInterceptorSupport<QueryMessage<?,?>>

Parameters:

interceptor - the interceptor to invoke when sending a Query

Returns:

handle to deregister the interceptor