Simple implementation of Java event monitoring

Some basics we need to know about event listening.

a) Three elements of the event:

source --     event source
when        --     the time when the event occurred
message     -- the event topic message, that is, the information that you want to pass through the event

 

b) Event flow process:

(1) Event source registration listener -> (2) event occurrence -> (3) notification listener -> (4) listener processing

 

So based on the above background knowledge, let's implement a simple listener and test the complete process of event monitoring.

Design a simple and reasonable event carrier according to the three elements of the event: Event

public class Event implements Serializable {

    private Object source;
    
    private Date when;
    
    private String message;
    
    public Object getSource() {
        return source;
    }

    public void setSource(Object source) {
        this.source = source;
    }
    
    public Date getWhen() {
        return when;
    }

    public void setWhen(Date when) {
        this.when = when;
    }
    
    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }
}

 

  Listener interface: EventListener

public interface EventListener {

    void handleEvent(Event event);
}

 

Listener implementation: MyListener

public class MyListener implements EventListener {

    private Log log = LogFactory.getLog(getClass());

    private SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");

    @Override
    public void handleEvent(Event event) {
        log.info("source: " + event.getSource() + ", message: " + event.getMessage() + ", when: "
                + sdf.format(event.getWhen()));
    }

}

 

In order to standardize, we formulate an event source interface here: EventSource

public interface EventSource {

    void registerListener(EventListener listener);
    
    void notifyListener();
}

 

Event source for writing tests: MySource

public class MySource implements EventSource {

    private EventListener listener;

    private int value;

    @Override
    public void registerListener(EventListener listener) {
        this.listener = listener;
    }

    @Override
    public void notifyListener() {
        if (listener == null)
            return;
        Event event = new Event();
        event.setSource(this);
        event.setWhen(new Date());
        event.setMessage("setValue " + value);
        listener.handleEvent(event);
    }

    public int getValue() {
        return value;
    }

    public void setValue(int value) {
        this.value = value;
        notifyListener();
    }

    public static void main(String[] args) {
        MySource source = new MySource();
        MyListener listener = new MyListener();
        source.registerListener(listener);
        source.setValue(100);
    }
}

 

Test output:

[INFO]-[MyListener-handleEvent(16)]: source: com.lichmama.event.MySource@2019a9d1, message: setValue 100, when: 2018-05-01 01:18:35