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I am trying to implement an event framework using spring events.I came to know that the default behavior of spring event framework is sync. But during spring context initialization if it finds a bean with id applicationEventMulticaster it behaves Async.

Now i want to have both sync and async event publishers in my application, because some of the events needs to be published sync. I tried to configure sync event multicaster using SysncTaskExecutor, but i cant find a way to inject it into my AsyncEventPublisher's applicationEventPublisher property. My spring configuration file is as below

<bean id="taskExecutor" class="org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor" destroy-method="shutdown">
        <property name="corePoolSize" value="5" />
        <property name="maxPoolSize" value="10" />
        <property name="WaitForTasksToCompleteOnShutdown" value="true" />
    </bean>  

    <bean id="syncTaskExecutor" class="org.springframework.core.task.SyncTaskExecutor" />

    <bean id="customEventPublisher" class="x.spring.event.CustomEventPublisher" />
    <bean id="customEventHandler" class="x.spring.event.CustomEventHandler" />  
    <bean id="eventSource" class="x.spring.event.EventSource" /> 
    <bean id="responseHandler" class="x.spring.event.ResponseHandler" /> 
    <bean id="syncEventSource" class="x.spring.event.syncEventSource" /> 


    <bean id="applicationEventMulticaster" class="org.springframework.context.event.SimpleApplicationEventMulticaster">
        <property name="taskExecutor" ref="taskExecutor" />         
    </bean>    

    <bean id="syncApplicationEventMulticaster" class="org.springframework.context.event.SimpleApplicationEventMulticaster">
        <property name="taskExecutor" ref="syncTaskExecutor" />         
    </bean>

Can anyone help me out here ?

  • What you want is, imho, easy enough your code/configuration is confusing though. You need to create your own implementation of the `ApplicationEventMulticaster` interface, which delegates certain calls to both the sync and async version and the `multicastEvent` only to the one you want. – M. Deinum Nov 11 '14 at 12:41
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    Though the question is very old adding the link for reference https://stackoverflow.com/questions/62917851/is-it-possible-to-support-sync-and-async-application-events-in-spring5 – Zuned Ahmed Aug 09 '20 at 01:50

4 Answers4

8

I just had to work this out for myself. By default events are sent asynchronously except if you implement a marker interface, in my case I called it SynchronousEvent. You'll need an 'executor' in your config too (I omitted mine as it's quite customised). 

@EnableAsync
@SpringBootConfiguration
public class BigFishConfig {

    @Autowired AsyncTaskExecutor executor;

    @Bean
    public ApplicationEventMulticaster applicationEventMulticaster() {
        log.debug("creating multicaster");
        return new SimpleApplicationEventMulticaster() {
            @Override
            public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) {
                ResolvableType type = eventType != null ? eventType : ResolvableType.forInstance(event);
                if (event instanceof PayloadApplicationEvent 
                        && ((PayloadApplicationEvent<?>) event).getPayload() instanceof SynchronousEvent) 
                    getApplicationListeners(event, type).forEach(l -> invokeListener(l, event));
                else 
                    getApplicationListeners(event, type).forEach(l -> executor.execute(() -> invokeListener(l, event)));
            }
        };
    }
...
Michael
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4

no, you can't do that, the spring initApplicationEventMulticaster just init only one, and the BeanName must be applicationEventMulticaster. so you just can choose one of below Executor:

- org.springframework.core.task.SyncTaskExecutor

- org.springframework.core.task.SimpleAsyncTaskExecutor

- your own Executor: org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor

any way, you can modify org.springframework.context.event.SimpleApplicationEventMulticaster to add your logic, then you can control whether need to Sync/Async

    /**
 * Initialize the ApplicationEventMulticaster.
 * Uses SimpleApplicationEventMulticaster if none defined in the context.
 * @see org.springframework.context.event.SimpleApplicationEventMulticaster
 */
protected void initApplicationEventMulticaster() {
    ConfigurableListableBeanFactory beanFactory = getBeanFactory();
    if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
        this.applicationEventMulticaster =
                beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
        if (logger.isDebugEnabled()) {
            logger.debug("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
        }
    }
    else {
        this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
        beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
        if (logger.isDebugEnabled()) {
            logger.debug("Unable to locate ApplicationEventMulticaster with name '" +
                    APPLICATION_EVENT_MULTICASTER_BEAN_NAME +
                    "': using default [" + this.applicationEventMulticaster + "]");
        }
    }
}
zg_spring
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  • I am fairly new guy to spring, but i think what you have suggested is fair enough.Can you please define significance difference between these three approaches and their appropriate use case ?Will appreciate it ! –  Nov 12 '14 at 06:04
2

i am not good for edit with stackoverflow. please forgive me.

  1. SyncTaskExecutor

I don't need to add comment that you can know well. this is synchronized. this Executor run task in sequence, and blocked for every task.

 public class SyncTaskExecutor implements TaskExecutor, Serializable {

/**
 * Executes the given {@code task} synchronously, through direct
 * invocation of it's {@link Runnable#run() run()} method.
 * @throws IllegalArgumentException if the given {@code task} is {@code null}
 */
@Override
public void execute(Runnable task) {
    Assert.notNull(task, "Runnable must not be null");
    task.run();
}

}

  1. SimpleAsyncTaskExecutor

This class is very large, so i just choose section of code. If you give threadFactory, will be retrieved Thread from this factory, or will be create new Thread.

    protected void doExecute(Runnable task) {
    Thread thread = (this.threadFactory != null ? this.threadFactory.newThread(task) : createThread(task));
    thread.start();
}
  1. ThreadPoolTaskExecutor

this class use jdk5's current pkg ThreadPoolTaskExecutor. but spring encapsulate functionality. Spring is good at this way, jdk6's current and jdk7'scurrent pkg have some difference. this will be get Thread from ThreadPool and reuse it, execute every task Asynchronized. If you want to know more detail, see JKD source code.

zg_spring
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  • Excellent. Prefer to write comment, if you are explaining something other then answer –  Nov 12 '14 at 11:03
  • hehe, i am a newer in stackoverflow, so try to find friends here. – zg_spring Nov 13 '14 at 03:33
  • Off course u r. A friend can suggest things to other friend, take it easy ! The reason for my suggestion was if somebody may downgrade u on yr above expatiation, u will loose yr credit. –  Nov 13 '14 at 06:43
-1

I tried below tutorial :

https://www.keyup.eu/en/blog/101-synchronous-and-asynchronous-spring-events-in-one-application

It helps in making sync and async multicaster and creates a wrapper over these. Make sure the name of the wrapper class (DistributiveEventMulticaster) is applicationEventMulticaster

munish
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