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/*
 * Copyright (c) 2020. AxonIQ
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package io.axoniq.axonserver.connector.query;

import io.axoniq.axonserver.connector.Registration;
import io.axoniq.axonserver.connector.ReplyChannel;
import io.axoniq.axonserver.grpc.query.QueryRequest;
import io.axoniq.axonserver.grpc.query.QueryResponse;
import io.axoniq.axonserver.grpc.query.QueryUpdate;
import io.axoniq.axonserver.grpc.query.SubscriptionQuery;

/**
 * Interface representing a component that can handle queries.
 */
@FunctionalInterface
public interface QueryHandler {

    /**
     * Handle the given {@code query}, using given {@code responseHandler} to send the response(s).
     * 

* Note that the query must be completed using {@link ReplyChannel#complete()} or {@link * ReplyChannel#sendLast(Object)}. * * @param query the message representing the query request * @param responseHandler to handler to send responses with */ void handle(QueryRequest query, ReplyChannel responseHandler); /** * Registers an incoming subscription query request, represented by given {@code query}, using given {@code * updateHandler} to send updates when the projection for this query changes. *

* If this handler doesn't support subscription queries for the given {@code query}, it should return {@code null}. * Otherwise, it must return a handle that can be used to cancel the subscription query. * * @param query the message representing the query * @param updateHandler to handler to send updates with * @return a registration to cancel the subscription, or {@code null} if this handler doesn't support the * subscription query */ default Registration registerSubscriptionQuery(SubscriptionQuery query, UpdateHandler updateHandler) { return null; } /** * Interface describing a stream of updates to a subscription query. */ interface UpdateHandler { /** * Send the given {@code queryUpdate} in response to the subscription query this handler was provided for. * * @param queryUpdate the update to send */ void sendUpdate(QueryUpdate queryUpdate); /** * Indicates the subscription query has completed, meaning no more updates are to be expected. The component * sending the subscription query is requested to close the subscription. */ void complete(); } }





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