Package io.axoniq.framework.springcloud.query

Class SpringCloudQueryController

java.lang.Object

io.axoniq.framework.springcloud.query.SpringCloudQueryController

@RestController
@RequestMapping("${axon.springcloud.query-endpoint:/axoniq-springcloud/query}")
public class SpringCloudQueryController
extends Object

Receives queries sent by other members of the cluster over HTTP, answering them with a stream of responses.

Every member must expose this endpoint under the same path, since that is how members reach each other; the path is the value of the axon.springcloud.query-endpoint property, defaulting to DEFAULT_QUERY_ENDPOINT. Subscription queries are received one level below it, under SUBSCRIPTION_PATH. This controller is registered by the Spring Boot autoconfiguration.

A query is answered with a Server-Sent Events stream rather than one reply, because a query may be answered any number of times. The stream releases the container thread as soon as it is returned, so a member answering a long-running query does not hold one thread per query in flight.

Since:

5.4.0

Author:

Allard Buijze

Field Summary

Fields

Modifier and Type	Field	Description
static final String	DEFAULT_QUERY_ENDPOINT	The path queries are received under when none is configured.
static final String	SUBSCRIPTION_PATH	The path, relative to the query endpoint, subscription queries are received under.

Constructor Summary

Constructors

Constructor	Description
SpringCloudQueryController(IncomingQueryInvoker invoker, ScheduledExecutorService scheduler, Executor keepAliveExecutor, SpringCloudQueryControllerConfiguration configuration)	Constructs a SpringCloudQueryController handing received queries to the given invoker.

Method Summary

Modifier and Type	Method	Description
org.springframework.web.servlet.mvc.method.annotation.SseEmitter	receiveQuery(QueryDispatchRequest request)	Handles the given request, sent by another member of the cluster.
org.springframework.web.servlet.mvc.method.annotation.SseEmitter	receiveSubscriptionQuery(SubscriptionQueryRequest request)	Handles the given subscription request, sent by another member of the cluster.

Methods inherited from class java.lang.Object

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

Field Details

DEFAULT_QUERY_ENDPOINT

public static final String DEFAULT_QUERY_ENDPOINT

The path queries are received under when none is configured.

See Also:

• Constant Field Values

SUBSCRIPTION_PATH

public static final String SUBSCRIPTION_PATH

The path, relative to the query endpoint, subscription queries are received under.

See Also:

• Constant Field Values

Constructor Details

SpringCloudQueryController

public SpringCloudQueryController(IncomingQueryInvoker invoker,
 ScheduledExecutorService scheduler,
 Executor keepAliveExecutor,
 SpringCloudQueryControllerConfiguration configuration)

Constructs a SpringCloudQueryController handing received queries to the given invoker.

The scheduler only ever decides when an open subscription is due a keep-alive, and never performs the write, so that a subscriber which has stopped reading cannot block whatever else the scheduler carries. The writes run on the keepAliveExecutor instead. Each is a blocking write to one subscriber, so an executor that can hold as many blocked threads as there are open subscriptions suits it, a virtual-thread-per-task executor for instance.

Parameters:

invoker - the component invoking this application's local query handler

scheduler - decides when each open subscription is due a keep-alive

keepAliveExecutor - performs the keep-alive writes

configuration - the SpringCloudQueryControllerConfiguration holding how long a response stream may stay open and how often an idle subscription is written to

Method Details

receiveQuery

@PostMapping(produces="text/event-stream")
public org.springframework.web.servlet.mvc.method.annotation.SseEmitter receiveQuery(@RequestBody
 QueryDispatchRequest request)

Handles the given request, sent by another member of the cluster.

Parameters:

request - the query sent by another member

Returns:

the stream carrying the responses to the query

receiveSubscriptionQuery

@PostMapping(path="/subscription",
             produces="text/event-stream")
public org.springframework.web.servlet.mvc.method.annotation.SseEmitter receiveSubscriptionQuery(@RequestBody
 SubscriptionQueryRequest request)

Handles the given subscription request, sent by another member of the cluster.

The stream carrying it has no timeout: a subscription lasts until the subscriber releases it or this member fails it, and a member that is simply not emitting updates is behaving correctly. What stands in for a timeout is the keep-alive written while it is idle, which stops as soon as the subscriber stops reading.

Parameters:

request - the subscription query sent by another member

Returns:

the stream carrying the initial result and the updates that follow it