001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    package org.apache.commons.monitoring.gauges;
018    
019    import org.apache.commons.monitoring.Role;
020    import org.apache.commons.monitoring.repositories.Repository;
021    
022    import java.util.LinkedList;
023    import java.util.ServiceLoader;
024    
025    public interface Gauge {
026        Role role();
027        double value();
028        long period();
029    
030        public static class LoaderHelper {
031            private LinkedList<Gauge> gauges = new LinkedList<Gauge>();
032    
033            public LoaderHelper(final boolean excludeParent, final String... includedPrefixes) {
034                final ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
035    
036                for (final Gauge g : ServiceLoader.load(Gauge.class, classLoader)) {
037                    addGaugeIfNecessary(classLoader, g, excludeParent, includedPrefixes);
038                }
039                for (final GaugeFactory gf : ServiceLoader.load(GaugeFactory.class, classLoader)) {
040                    for (final Gauge g : gf.gauges()) {
041                        addGaugeIfNecessary(classLoader, g, excludeParent, includedPrefixes);
042                    }
043                }
044            }
045    
046            private void addGaugeIfNecessary(final ClassLoader classLoader, final Gauge g, final boolean excludeParent, final String... prefixes) {
047                final Class<? extends Gauge> gaugeClass = g.getClass();
048                if (!excludeParent || gaugeClass.getClassLoader() == classLoader) {
049                    if (prefixes != null) {
050                        for (final String p : prefixes) {
051                            if (!gaugeClass.getName().startsWith(p)) {
052                                return;
053                            }
054                        }
055                    }
056                    Repository.INSTANCE.addGauge(g);
057                    gauges.add(g);
058                }
059            }
060    
061            public void destroy() {
062                for (final Gauge gauge : gauges) {
063                    Repository.INSTANCE.stopGauge(gauge.role());
064                }
065            }
066        }
067    }