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'databene commons' is an open source Java library by Volker Bergmann. It provides extensions to the Java core library by utility classes, abstract concepts and concrete implementations.

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/*
 * Copyright (C) 2004-2015 Volker Bergmann ([email protected]).
 * All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * http://www.apache.org/licenses/LICENSE-2.0
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.databene.commons.debug;

import java.util.ArrayList;
import java.util.List;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Class that monitors resources as a collection of {@link MonitoredResource}s.
 * Resources are registered and unregistered with {@link #register(Object)} and
 * {@link #unregister(Object)} and in the end you can assert that all resources 
 * have been unregistered by calling {@link #assertNoRegistrations(boolean)}.
 * Created: 14.04.2011 17:16:20
 * @since 0.5.8
 * @author Volker Bergmann
 */
public class ResourceMonitor {
	
	private static final Logger LOGGER = LoggerFactory.getLogger(ResourceMonitor.class);
	
	private List registrations;
	
	public ResourceMonitor() {
		registrations = new ArrayList();
	}

	public void register(Object object) {
		Throwable t = new Throwable();
		registrations.add(new MonitoredResource(object, t.getStackTrace()));
	}
	
	public void unregister(Object object) {
		for (int i = registrations.size() - 1; i >= 0; i--) {
			MonitoredResource candidate = registrations.get(i);
			if (candidate.resource == object) {
				registrations.remove(i);
				return;
			}
		}
		throw new IllegalStateException("Object '" + object + "' was not registered");
	}
	
	public List getRegistrations() {
		return registrations;
	}
	
	public void reset() {
		this.registrations.clear();
	}
	
	public boolean assertNoRegistrations(boolean critical) {
		if (registrations.size() == 0)
			return true;
		String message = "There are resources which have not been unregistered:";
		LOGGER.warn(message);
		logRegistrations();
		if (critical)
			throw new IllegalStateException(message);
		return false;
	}

	private void logRegistrations() {
		for (MonitoredResource resource : registrations) {
			LOGGER.warn(resource.toString());
		}
	}

}