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Unit Standard (JSR 363) Reference Implementation.
/**
* Unit-API - Units of Measurement API for Java
* Copyright (c) 2005-2015, Jean-Marie Dautelle, Werner Keil, V2COM.
*
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
*
* 3. Neither the name of JSR-363 nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
* EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package tec.units.ri.spi;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Objects;
import java.util.ServiceLoader;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.measure.spi.ServiceProvider;
/**
* This singleton provides access to the services available in the current runtime environment and context. The
* behavior can be adapted, by calling {@link #init(ServiceProvider)} before accessing any measurement
* services.
*
* @author Werner Keil
*/
public final class Bootstrap {
/**
* The ServiceProvider used.
*/
private static volatile ServiceProvider serviceProviderDelegate;
/**
* The shared lock instance user.
*/
private static final Object LOCK = new Object();
/**
* Private singletons constructor.
*/
private Bootstrap() {
}
/**
* Load the {@link ServiceProvider} to be used.
*
* @return {@link ServiceProvider} to be used for loading the services.
*/
@SuppressWarnings("LoopStatementThatDoesntLoop")
private static ServiceProvider loadDefaultServiceProvider() {
try {
for (ServiceProvider sp : ServiceLoader.load(ServiceProvider.class)) {
return sp;
}
} catch (Exception e) {
Logger.getLogger(Bootstrap.class.getName()).log(Level.INFO,"No ServiceProvider loaded, using default.");
}
return new DefaultServiceProvider();
}
/**
* Replace the current {@link ServiceProvider} in use.
*
* @param serviceProvider the new {@link ServiceProvider}
* @return the removed , or null.
*/
public static ServiceProvider init(ServiceProvider serviceProvider) {
Objects.requireNonNull(serviceProvider);
synchronized (LOCK) {
if (Bootstrap.serviceProviderDelegate==null) {
Bootstrap.serviceProviderDelegate = serviceProvider;
Logger.getLogger(Bootstrap.class.getName())
.log(Level.INFO,"Unit Bootstrap: new ServiceProvider set: " + serviceProvider.getClass().getName());
return null;
} else {
ServiceProvider prevProvider = Bootstrap.serviceProviderDelegate;
Bootstrap.serviceProviderDelegate = serviceProvider;
Logger.getLogger(Bootstrap.class.getName())
.log(Level.WARNING, "Unit Bootstrap: ServiceProvider replaced: " + serviceProvider.getClass().getName());
return prevProvider;
}
}
}
/**
* Ge {@link ServiceProvider}. If necessary the {@link ServiceProvider} will be lazily loaded.
*
* @return the {@link ServiceProvider} used.
*/
static ServiceProvider getServiceProvider() {
if (serviceProviderDelegate==null) {
synchronized (LOCK) {
if (serviceProviderDelegate==null) {
serviceProviderDelegate = loadDefaultServiceProvider();
}
}
}
return serviceProviderDelegate;
}
/**
* Delegate method for {@link ServiceProvider#getServices(Class)}.
*
* @param serviceType the service type.
* @return the services found.
* @see ServiceProvider#getServices(Class)
*/
public static Collection getServices(Class serviceType) {
return getServiceProvider().getServices(serviceType);
}
/**
* Delegate method for {@link ServiceProvider#getServices(Class)}.
*
* @param serviceType the service type.
* @return the service found, or {@code null}.
* @see ServiceProvider#getServices(Class)
*/
public static T getService(Class serviceType) {
List services = getServiceProvider().getServices(serviceType);
if(services.isEmpty()){
return null;
}
services = new ArrayList(services);
Collections.sort(services, new Comparator() {
@Override
public int compare(T a1, T a2) {
return a1.getClass().getSimpleName().compareTo(a2.getClass().getSimpleName());
}
});
return services.get(0);
}
}