"Bird-java" event bus between distributed services Eventbus

Tag: false getc Style time () Targe ref event Send identity

What is Eventbus
Eventbus is an implementation of the publish-subscribe pattern. It realizes the decoupling and communication between components in a very elegant way, and it is widely used in the fields of Android development, DDD and so on.

The event flow is roughly as follows:

• Producer sends an event to Eventbus.
• Eventbus pushes events to all consumer that have listened to the event.
• A consumer consumption event was monitored for this event.

Note: A component can be either a producer or a consumer.

The Eventbus between distributed services
In distributed systems, the delivery of events between services is much more complex than single-machine eventbus. Is there a eventbus for distributed services, and event passing is as simple as a single machine? Search the Java implementation of Eventbus on GitHub, the top ten are almost all for Android or Java single-machine event bus. After a long ... Let's do it yourself. The Eventbus in a clustered environment will require more consideration than the standalone version, such as:

1. In the case of a service cluster deployment, how to ensure that each cluster can subscribe to the event, and that each cluster can consume the event only once.
2. How to implement a service within multiple ' xxxservice ' subscriptions to the same event.

Solution:

1. Using ' Kafka ' to implement a publish subscription between clusters (based on ' topic '), the same cluster is in the same Kafka Consumer-group to ensure that each cluster consumes only one event at a time.
2. The service can be reflected at startup to get all classes that implement the ' ieventhandler<teventarg> ' and cache, and the service consumes the message when it gets all the handler that registered the message and calls its ' handleevent ' method.

Some key source code

1. Definition of event message

 Public Abstract classEventArgImplementsieventarg{PrivateDate eventtime;  PublicEventArg () {eventtime=NewDate (); }     PublicDate Geteventtime () {returneventtime; }     Public voidseteventtime (Date eventtime) { This. Eventtime =eventtime; }}

Event message Default record creation time, can extend other fields, such as Send time, identity, etc.

2. Send messages using Spring-kafka

/*** Kafka Event Registrar, push message to Kafka queue*/@Component Public classKafkaregisterImplementsIeventregister {@Autowired (required=false)    PrivateKafkatemplate<string,ieventarg>kafkatemplate; /*** Event Registration * *@paramEventArg Event Parameters*/@Override Public voidregist (Ieventarg eventarg) {kafkatemplate.send (Gettopic (EventArg), EventArg); }    /*** Get Kafka's topic * *@paramEventArg *@returnTopic*/    PrivateString gettopic (Ieventarg eventarg) {returnEventarg.getclass (). GetName (); }}

3. Consume Kafka messages and perform all events subscribed to the message in the current service

/*** Kafka Event Listener*/ Public classKafkaeventarglistenerImplementsMessagelistener<string,eventarg>{@AutowiredPrivateieventhandlerfactory eventhandlerfactory; @Override Public voidOnMessage (consumerrecord<string, eventarg>Consumerrecord) {        if(Consumerrecord = =NULL)return; EventArg value=Consumerrecord.value (); Set<IEventHandler> handlers =eventhandlerfactory.gethandlers (value); if(Handlers = =NULL)return;  for(Ieventhandler handler:handlers) {handler.        Handleevent (value); }    }}

Use of Eventbus

1, the definition of the event. All events are inherited from the EventArg abstract class above, as shown in the following example:

 Public class extends eventarg{    private  String value;      Public String GetValue () {        return  value;    }      Public void SetValue (String value) {        this. Value = value;    }} 

2, Event release. Example code:

Eventbus.push (new testeventarg ());

3, event subscription. After a service publishing event, any ' Xxxserviceimpl ' class in any service can subscribe to the event, implementing the ' ieventhandler<teventarg> ' interface to complete the subscription to the event, as shown in the following example:

 Public class extends Implements Formservice,ieventhandler<testeventarg> {    @Override    publicvoid  Handleevent (Testeventarg eventarg) {        System.out.println ("Notify zero======");}    }

Overall, the use is still very simple, eventbus implementation and use examples are included in the Bird-java Project, Project address: Https://github.com/liuxx001/bird-java.

"Bird-java" event bus between distributed services Eventbus