使用reactor eventbus进行事件驱动开发

maven

        <dependency>
            <groupId>io.projectreactor</groupId>
            <artifactId>reactor-bus</artifactId>
        </dependency>

config

@Configuration
public class EventConfig {

    @Bean
    Environment environment() {
        return Environment.initializeIfEmpty().assignErrorJournal();
    }

    @Bean
    @Autowired
    public EventBus eventBus(Environment environment, MyEventListener myEventListener) {
        EventBus eventBus = EventBus.create(environment, Environment.THREAD_POOL);

        eventBus.on($("myevent"), myEventListener);

        return eventBus;
    }
}

env的默认配置从reactor-core-2.0.8.RELEASE.jar!/META-INF/reactor/reactor-environment.properties中读取

#
# Copyright (c) 2011-2015 Pivotal Software Inc., Inc. All Rights Reserved.
#
# 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.
#

##
# Dispatcher configuration
#
# Each dispatcher must be configured with a type:
#
# reactor.dispatchers.<name>.type = <type>
#
# Legal values for <type> are dispatcherGroup, ringBuffer, synchronous, and workQueue.

# Depending on the type, further configuration is be possible:
#
# reactor.dispatchers.<name>.size:    dispatcherGroup and workQueue Dispatchers
# reactor.dispatchers.<name>.backlog: dispatcherGroup, ringBuffer, and workQueue Dispatchers
#
# A size less than 1 may be specified to indicate that the size should be the same as the number
# of CPUs.

# A thread pool executor dispatcher, named threadPoolExecutor
reactor.dispatchers.threadPoolExecutor.type = threadPoolExecutor
reactor.dispatchers.threadPoolExecutor.size = 0
# Backlog is how many Task objects to warm up internally
reactor.dispatchers.threadPoolExecutor.backlog = 2048

# A group of dispatchers replicated from the default dispatcher, named dispatcherGroup
reactor.dispatchers.dispatcherGroup.type = dispatcherGroup
reactor.dispatchers.dispatcherGroup.size = 0
reactor.dispatchers.dispatcherGroup.backlog = 2048

# A ring buffer dispatcher, named ringBuffer
reactor.dispatchers.shared.type = ringBuffer
reactor.dispatchers.shared.backlog = 8192

# A work queue dispatcher, named workQueue
reactor.dispatchers.workQueue.type = workQueue
reactor.dispatchers.workQueue.size = 0
reactor.dispatchers.workQueue.backlog = 2048

# The dispatcher named shared should be the default dispatcher
reactor.dispatchers.default = shared

event listener

@Component
public class MyEventListener implements Consumer<Event<MyEvent>> {

    private static final Logger LOGGER = LoggerFactory.getLogger(MyEventListener.class);

    @Override
    public void accept(Event<MyEvent> eventContextEvent) {

        MyEvent event = eventContextEvent.getData();

        LOGGER.info("thread {} ,receive event:{}",Thread.currentThread().getName(),event.getData());
    }
}

publish event

    @Autowired
    EventBus eventBus;

    public void publishEvent(String data){
        eventBus.notify("myevent", Event.wrap(new MyEvent(data)));
    }

ThreadPoolExecutorDispatcher

reactor-core-2.0.8.RELEASE-sources.jar!/reactor/core/dispatch/ThreadPoolExecutorDispatcher.java
在reactor-core-2.0.8.RELEASE-sources.jar!/reactor/Environment.java创建默认的ThreadPoolExecutorDispatcher

private static ThreadPoolExecutorDispatcher createThreadPoolExecutorDispatcher(DispatcherConfiguration dispatcherConfiguration) {
        int size = getSize(dispatcherConfiguration, 0);
        int backlog = getBacklog(dispatcherConfiguration, 128);

        return new ThreadPoolExecutorDispatcher(size, backlog, dispatcherConfiguration.getName());
    }

构造器

/**
     * Create a new {@literal ThreadPoolExecutorDispatcher} with the given size, backlog, name, and {@link
     * java.util.concurrent.RejectedExecutionHandler}.
     *
     * @param poolSize
     *         the pool size
     * @param backlog
     *         the backlog size
     * @param threadName
     *         the name prefix to use when creating threads
     */
    public ThreadPoolExecutorDispatcher(int poolSize,
                                        int backlog,
                                        String threadName) {
        this(poolSize,
             backlog,
             threadName,
             new LinkedBlockingQueue<Runnable>(backlog),
             new RejectedExecutionHandler() {
                 @Override
                 public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
                     r.run();
                 }
             });
    }

默认采用的是LinkedBlockingQueue，大小为配置文件指定的backlog，RejectedExecutionHandler采用的是调用者执行。

/**
     * A handler for rejected tasks that runs the rejected task
     * directly in the calling thread of the {@code execute} method,
     * unless the executor has been shut down, in which case the task
     * is discarded.
     */
    public static class CallerRunsPolicy implements RejectedExecutionHandler {
        /**
         * Creates a {@code CallerRunsPolicy}.
         */
        public CallerRunsPolicy() { }

        /**
         * Executes task r in the caller's thread, unless the executor
         * has been shut down, in which case the task is discarded.
         *
         * @param r the runnable task requested to be executed
         * @param e the executor attempting to execute this task
         */
        public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
            if (!e.isShutdown()) {
                r.run();
            }
        }
    }

因此，队列没有满的时候是异步的，满的时候就阻塞了。

doc

• Creating an Asynchronous, Event-Driven Application with Reactor

• Reactor 指南中文版 V2.0