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.filter;

import ch.qos.logback.core.boolex.EvaluationException;
import ch.qos.logback.core.boolex.EventEvaluator;
import ch.qos.logback.core.spi.FilterReply;

The value of the AbstractMatcherFilter<E>.onMatch and AbstractMatcherFilter<E>.onMismatch attributes is set to FilterReply.NEUTRAL, so that a badly configured evaluator filter does not disturb the functioning of the filter chain. 
It is expected that one of the two attributes will have its value changed to FilterReply.ACCEPT or FilterReply.DENY. That way, it is possible to decide if a given result must be returned after the evaluation either failed or succeeded. 
 For more information about filters, please refer to the online manual at
http://logback.qos.ch/manual/filters.html
Author:
Ceki Gülcü, Sébastien Pennec/**
 * The value of the {@link #onMatch} and {@link #onMismatch} attributes is set
 * to {@link FilterReply#NEUTRAL}, so that a badly configured evaluator filter does
 * not disturb the functioning of the filter chain. 
 * 
 * <p>It is expected that one of the two attributes will have its value changed
 * to {@link FilterReply#ACCEPT} or {@link FilterReply#DENY}. That way, it is possible to
 * decide if a given result must be returned after the evaluation either failed
 * or succeeded.
 * 
 * 
 * <p> For more information about filters, please refer to the online manual at
 * http://logback.qos.ch/manual/filters.html
 * 
 * @author Ceki G&uuml;lc&uuml;
 * @author S&eacute;bastien Pennec
 */
public class EvaluatorFilter<E> extends AbstractMatcherFilter<E> {

    EventEvaluator<E> evaluator;

    @Override
    public void start() {
        if (evaluator != null) {
            super.start();
        } else {
            addError("No evaluator set for filter " + this.getName());
        }
    }

    public EventEvaluator<E> getEvaluator() {
        return evaluator;
    }

    public void setEvaluator(EventEvaluator<E> evaluator) {
        this.evaluator = evaluator;
    }

    public FilterReply decide(E event) {
        // let us not throw an exception
        // see also bug #17.
        if (!isStarted() || !evaluator.isStarted()) {
            return FilterReply.NEUTRAL;
        }
        try {
            if (evaluator.evaluate(event)) {
                return onMatch;
            } else {
                return onMismatch;
            }
        } catch (EvaluationException e) {
            addError("Evaluator " + evaluator.getName() + " threw an exception", e);
            return FilterReply.NEUTRAL;
        }
    }

}