How to do it...

This recipe will show you one of the main features introduced by CDI 2.0: ordered observers. Now, you can turn the observer's job into something predictable:

1. First, let's create an event to be observed:

public class MyEvent {
    
    private final String value;
    
    public MyEvent(String value){
        this.value = value;
    }
    
    public String getValue(){
        return value;
    }
}

2. Now, we build our observers and the server that will fire them:

public class OrderedObserver {

    public static void main(String[] args){
        try(SeContainer container =    
        SeContainerInitializer.newInstance().initialize()){
            container
                .getBeanManager()
                .fireEvent(new MyEvent("event: " + 
                System.currentTimeMillis()));
        }
    }
 
    public void thisEventBefore(
            @Observes @Priority(Interceptor.Priority
            .APPLICATION - 200) 
            MyEvent event){
        
        System.out.println("thisEventBefore: " + event.getValue());
    }
 
    public void thisEventAfter(
            @Observes @Priority(Interceptor.Priority
           .APPLICATION + 200) 
            MyEvent event){
        
        System.out.println("thisEventAfter: " + event.getValue());
    }  
}

3. Also, don't forget to add the beans.xml file to the META-INF folder:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://xmlns.jcp.org/xml/ns/javaee"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee 
       http://xmlns.jcp.org/xml/ns/javaee/beans_1_1.xsd"
       bean-discovery-mode="all">
</beans>

4. Once you run it, you should see a result like this:

INFO: WELD-ENV-002003: Weld SE container 
353db40d-e670-431d-b7be-4275b1813782 initialized
 thisEventBefore: event -> 1501818268764
 thisEventAfter: event -> 1501818268764

Now, let's see how this works.