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package javax.servlet;

import java.util.EventListener;

Interface for receiving notification events about ServletContext
attribute changes.
In order to receive these notification events, the implementation class must be either declared in the deployment descriptor of the web application, annotated with WebListener, or registered via one of the addListener methods defined on ServletContext. 
The order in which implementations of this interface are invoked is
unspecified.
See Also:
ServletContextAttributeEvent
Since:
Servlet 2.3/**
 * Interface for receiving notification events about ServletContext
 * attribute changes.
 *
 * <p>In order to receive these notification events, the implementation
 * class must be either declared in the deployment descriptor of the web
 * application, annotated with {@link javax.servlet.annotation.WebListener},
 * or registered via one of the addListener methods defined on
 * {@link ServletContext}.
 *
 * <p>The order in which implementations of this interface are invoked is
 * unspecified.
 *
 * @see ServletContextAttributeEvent
 *
 * @since Servlet 2.3
 */

public interface ServletContextAttributeListener extends EventListener {

    
Receives notification that an attribute has been added to the
ServletContext.
Params:
event – the ServletContextAttributeEvent containing the
ServletContext to which the attribute was added, along with the
attribute name and value
Implementation Requirements:

The default implementation takes no action./**
     * Receives notification that an attribute has been added to the
     * ServletContext.
     *
     * @param event the ServletContextAttributeEvent containing the
     * ServletContext to which the attribute was added, along with the
     * attribute name and value
     *
     * @implSpec
     * The default implementation takes no action.
     */
    default public void attributeAdded(ServletContextAttributeEvent event) {}

    
Receives notification that an attribute has been removed
from the ServletContext.
Params:
event – the ServletContextAttributeEvent containing the
ServletContext from which the attribute was removed, along with
the attribute name and value
Implementation Requirements:

The default implementation takes no action./**
     * Receives notification that an attribute has been removed
     * from the ServletContext.
     *
     * @param event the ServletContextAttributeEvent containing the
     * ServletContext from which the attribute was removed, along with
     * the attribute name and value
     *
     * @implSpec
     * The default implementation takes no action.
     */
    default public void attributeRemoved(ServletContextAttributeEvent event) {}

    /*
     * Receives notification that an attribute has been replaced
     * in the ServletContext.
     *
     * @param event the ServletContextAttributeEvent containing the
     * ServletContext in which the attribute was replaced, along with
     * the attribute name and its old value
     *
     * @implSpec
     * The default implementation takes no action.
     */
    default public void attributeReplaced(ServletContextAttributeEvent event) {}
}