package ejava.examples.ejbsessionbank.ejb;
   
   import javax.annotation.PostConstruct;
   import javax.ejb.AccessTimeout;
   import javax.ejb.ConcurrencyManagement;
   import javax.ejb.ConcurrencyManagementType;
   import javax.ejb.Lock;
   import javax.ejb.LockType;
   import javax.ejb.Singleton;
  import javax.ejb.Startup;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * This class provides an example of a Singleton EJB. The container will
   * instantiate only one instance of this class and manage concurrent
   * access to the instance.
   */
  @Singleton
  //used to cause the singleton to be initialized during server startup --
  //otherwise it would be on demand
  @Startup
  //tells the container to manage concurrent access. Alternately we could use 
  //BEAN and standard Java concurrency managaement mechanisms
  @ConcurrencyManagement(ConcurrencyManagementType.CONTAINER)
  //establish an access timeout either at class or method level
  @AccessTimeout(value=3000)
  public class StatsEJB implements StatsLocal, StatsRemote {
  	static final Logger log = LoggerFactory.getLogger(StatsEJB.class);
  	private int delta;
  	private int total;
  	
  	@PostConstruct
  	public void init() {
  		log.info("*** StatsEJB ***");
  	}
  
  	/**
  	 * An example of a write method that the container will protect against
  	 * other write and readers.
  	 */
  	@Override
  	@Lock(LockType.WRITE)
  	public void open() {
  		this.delta += 1;
  		this.total += 1;
  		log.debug(String.format("open: stats=%d, total=%d", delta, total));
  	}
  	
  	@Override
  	@Lock(LockType.WRITE)
  	public void close() {
  		this.delta -= 1;
  		this.total += 1;
  		log.debug(String.format("close: stats=%d, total=%d", delta, total));
  	}	
  	
  	/**
  	 * An example read method that the container will protect from other
  	 * write methods, but allow concurrent read access.
  	 */
  	@Override
  	@Lock(LockType.READ)
  	public int getTotal() {
  		log.debug(String.format("getTotal: stats=%d, total=%d", delta, total));
  		return total;
  	}
  
  	@Override
  	@Lock(LockType.READ)
  	public int getDelta() {
  		log.debug(String.format("getDelta: stats=%d, total=%d", delta, total));
  		return delta;
  	}
  	
  	@Override
  	@Lock(LockType.WRITE)
  	public void reset() {
  		delta=0;
  		total=0;
  		log.debug(String.format("reset: stats=%d, total=%d", delta, total));
  	}
  }