Logback: the reliable, generic, fast and flexible logging framework.
Copyright (C) 1999-2015, QOS.ch. All rights reserved.
This program and the accompanying materials are dual-licensed under
either the terms of the Eclipse Public License v1.0 as published by
the Eclipse Foundation
  or (per the licensee's choosing)
under the terms of the GNU Lesser General Public License version 2.1
as published by the Free Software Foundation.
/**
 * Logback: the reliable, generic, fast and flexible logging framework.
 * Copyright (C) 1999-2015, QOS.ch. All rights reserved.
 *
 * This program and the accompanying materials are dual-licensed under
 * either the terms of the Eclipse Public License v1.0 as published by
 * the Eclipse Foundation
 *
 *   or (per the licensee's choosing)
 *
 * under the terms of the GNU Lesser General Public License version 2.1
 * as published by the Free Software Foundation.
 */
package ch.qos.logback.core.sift;

import ch.qos.logback.core.Appender;
import ch.qos.logback.core.Context;
import ch.qos.logback.core.CoreConstants;
import ch.qos.logback.core.helpers.NOPAppender;
import ch.qos.logback.core.joran.spi.JoranException;
import ch.qos.logback.core.spi.AbstractComponentTracker;
import ch.qos.logback.core.spi.ContextAwareImpl;

Track appenders by key. When an appender is not used for longer than ComponentTracker<Appender<E>>.DEFAULT_TIMEOUT it is stopped and removed. 
Author:
Tommy Becker, Ceki Gulcu, David Roussel/**
 * Track appenders by key. When an appender is not used for
 * longer than {@link #DEFAULT_TIMEOUT} it is stopped and removed.
 *
 * @author Tommy Becker
 * @author Ceki Gulcu
 * @author David Roussel
 */
public class AppenderTracker<E> extends AbstractComponentTracker<Appender<E>> {

    int nopaWarningCount = 0;

    final Context context;
    final AppenderFactory<E> appenderFactory;
    final ContextAwareImpl contextAware;

    public AppenderTracker(Context context, AppenderFactory<E> appenderFactory) {
        super();
        this.context = context;
        this.appenderFactory = appenderFactory;
        this.contextAware = new ContextAwareImpl(context, this);
    }

    @Override
    protected void processPriorToRemoval(Appender<E> component) {
        component.stop();
    }

    @Override
    protected Appender<E> buildComponent(String key) {
        Appender<E> appender = null;
        try {
            appender = appenderFactory.buildAppender(context, key);
        } catch (JoranException je) {
            contextAware.addError("Error while building appender with discriminating value [" + key + "]");
        }
        if (appender == null) {
            appender = buildNOPAppender(key);
        }

        return appender;
    }

    private NOPAppender<E> buildNOPAppender(String key) {
        if (nopaWarningCount < CoreConstants.MAX_ERROR_COUNT) {
            nopaWarningCount++;
            contextAware.addError("Building NOPAppender for discriminating value [" + key + "]");
        }
        NOPAppender<E> nopa = new NOPAppender<E>();
        nopa.setContext(context);
        nopa.start();
        return nopa;
    }

    @Override
    protected boolean isComponentStale(Appender<E> appender) {
        return !appender.isStarted();
    }

}