The Action interface is a part of the Logback configuration system and is used to represent an action that should be performed when a certain event occurs. Here's an example of how an Action class might be implemented:

import ch.qos.logback.core.spi.ContextAwareBase;
import ch.qos.logback.core.spi.LifeCycle;

public class MyAction extends ContextAwareBase implements Action, LifeCycle {
    private boolean started = false;
    
    @Override
    public void start() {
        started = true;
    }
 
    @Override
    public void stop() {
        started = false;
    }
 
    @Override
    public boolean isStarted() {
        return started;
    }
 
    @Override
    public void begin(String event, Object origin) {
        // Perform the action
        System.out.println("Event '" + event + "' occurred at " + origin);
    }
 
    @Override
    public void end(String event, Object origin) {
        // Perform any necessary cleanup
        System.out.println("Event '" + event + "' finished at " + origin);
    }
}

This example shows a basic implementation of the Action interface, which includes a begin() method that is called when the action is triggered and an end() method that is called when the action is finished.

This class can be declared in logback.xml, this way:

<configuration>
  <appender name="console" class="ch.qos.logback.core.ConsoleAppender">
    <encoder>
      <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
    </encoder>
    <onStart>
      <new class="com.example.MyAction"/>
    </onStart>
  </appender>
  <root level="info">
    <appender-ref ref="console"/>
  </root>
</configuration>

Here, the example creates an instance of MyAction class and register it in the appender's onStart action list. The begin() and end() method will be invoked when the appender is started and stopped respectively.

It's important to keep in mind that this is just an example of how the Action interface can be implemented, and that the actual implementation of your application may vary depending on your specific requirements.