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Using Camel with CDI
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/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.camel.cdi;

import java.util.ArrayList;
import java.util.List;
import javax.enterprise.event.Event;

import org.apache.camel.CamelContext;
import org.apache.camel.Consumer;
import org.apache.camel.Endpoint;
import org.apache.camel.Processor;
import org.apache.camel.Producer;
import org.apache.camel.impl.DefaultEndpoint;

/**
 * A Camel {@link Endpoint} that bridges the CDI events facility with Camel routes so that CDI events
 * can be seamlessly observed / consumed (respectively produced / fired) from Camel consumers (respectively by Camel producers).
 * 
 * The {@code CdiEventEndpoint} bean can be used to observe / consume CDI events whose event type is {@code T}, for example:
 * 

 * {@literal @}Inject
 * CdiEventEndpoint{@literal <}String{@literal >} cdiEventEndpoint;
 *
 * from(cdiEventEndpoint).log("CDI event received: ${body}");
 * 
 *
 * Conversely, the {@code CdiEventEndpoint} bean can be used to produce / fire CDI events whose event type is {@code T}, for example:
 * 
 * {@literal @}Inject
 * CdiEventEndpoint{@literal <}String{@literal >} cdiEventEndpoint;
 *
 * from("direct:event").to(cdiEventEndpoint).log("CDI event sent: ${body}");
 * 
 *
 * The type variable {@code T}, respectively the qualifiers, of a particular {@code CdiEventEndpoint} injection point
 * are automatically translated into the parameterized event type, respectively into the event qualifiers, e.g.:
 * 
 * {@literal @}Inject
 * {@literal @}FooQualifier
 * CdiEventEndpoint{@literal <}List{@literal <}String{@literal >}{@literal >} cdiEventEndpoint;
 *
 * from("direct:event").to(cdiEventEndpoint);
 *
 * void observeCdiEvents({@literal @}Observes {@literal @}FooQualifier List{@literal <}String{@literal >} event) {
 *     logger.info("CDI event: {}", event);
 * }
 * 
 *
 * When multiple Camel contexts exist in the CDI container, the {@code @ContextName} qualifier can be used
 * to qualify the {@code CdiEventEndpoint} injection points, e.g.:
 * 
 * {@literal @}Inject
 * {@literal @}ContextName("foo")
 * CdiEventEndpoint{@literal <}List{@literal <}String{@literal >}{@literal >} cdiEventEndpoint;
 *
 * // Only observe / consume events having the {@literal @}ContextName("foo") qualifier
 * from(cdiEventEndpoint).log("Camel context 'foo' > CDI event received: ${body}");
 *
 * // Produce / fire events with the {@literal @}ContextName("foo") qualifier
 * from("...").to(cdiEventEndpoint);
 *
 * void observeCdiEvents({@literal @}Observes {@literal @}ContextName("foo") List{@literal <}String{@literal >} event) {
 *     logger.info("Camel context 'foo' > CDI event: {}", event);
 * }
 * 
 */
public final class CdiEventEndpoint extends DefaultEndpoint {

    private final List> consumers = new ArrayList<>();

    private final Event event;

    CdiEventEndpoint(Event event, String endpointUri, CamelContext context, ForwardingObserverMethod observer) {
        super(endpointUri, context);
        this.event = event;
        observer.setObserver(this);
    }

    public Consumer createConsumer(Processor processor) {
        return new CdiEventConsumer<>(this, processor);
    }

    @Override
    public Producer createProducer() {
        return new CdiEventProducer<>(this, event);
    }

    @Override
    public boolean isSingleton() {
        return true;
    }

    void registerConsumer(CdiEventConsumer consumer) {
        synchronized (consumers) {
            consumers.add(consumer);
        }
    }

    void unregisterConsumer(CdiEventConsumer consumer) {
        synchronized (consumers) {
            consumers.remove(consumer);
        }
    }

    void notify(T t) {
        synchronized (consumers) {
            for (CdiEventConsumer consumer : consumers) {
                consumer.notify(t);
            }
        }
    }
}