ShellStatusProvider.java

package org.springframework.roo.shell.event;

/**
 * Implemented by shells that support the publication of shell status changes.
 * <p>
 * Implementations are not required to provide any guarantees with respect to
 * the order in which notifications are delivered to listeners.
 * <p>
 * Implementations must permit modification of the listener list, even while
 * delivering event notifications to listeners. However, listeners do not
 * receive any guarantee that their addition or removal from the listener list
 * will be effective or not for any event notification that is currently
 * proceeding.
 * <p>
 * Implementations must ensure that status notifications are only delivered when
 * an actual change has taken place.
 * 
 * @author Ben Alex
 * @since 1.0
 */
public interface ShellStatusProvider {

  /**
   * Registers a new status listener.
   * 
   * @param shellStatusListener to register (cannot be null)
   */
  void addShellStatusListener(ShellStatusListener shellStatusListener);

  /**
   * Returns the current shell status.
   * 
   * @return the current status (never null)
   */
  ShellStatus getShellStatus();

  /**
   * Removes an existing status listener.
   * <p>
   * If the presented status listener is not found, the method returns without
   * exception.
   * 
   * @param shellStatusListener to remove (cannot be null)
   */
  void removeShellStatusListener(ShellStatusListener shellStatusListener);
}