javax.measure.spi.ServiceProvider Maven / Gradle / Ivy
Show all versions of unit-api Show documentation
/*
* Units of Measurement API
* Copyright (c) 2014-2016, 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 javax.measure.spi;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.ServiceLoader;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.measure.Quantity;
import javax.measure.format.UnitFormat;
/**
* Service Provider for Units of Measurement services.
*
* All the methods in this class are safe for use by multiple concurrent threads.
*
* @version 0.9.3, July 2, 2016
* @author Werner Keil
* @author Martin Desruisseaux
*/
public abstract class ServiceProvider {
/**
* Synchronization lock for searching or setting the service providers.
*/
private static final Object LOCK = new Object();
/**
* All service providers found, sorted in preference order. Array content shall never been changed after initialization; if we want to change the
* array content, a new array shall be created.
*/
private static volatile ServiceProvider[] providers;
/**
* Creates a new service provider. Only to be used by subclasses.
*/
protected ServiceProvider() {
}
/**
* This method allows to define a priority for a registered ServiceProvider instance. When multiple providers are registered in the system the
* provider with the highest priority value is taken.
*
* @return the provider's priority (default is 0).
*/
public int getPriority() {
return 0;
}
/**
* Returns the service to obtain a {@link SystemOfUnits}, or {@code null} if none.
*
* @return the service to obtain a {@link SystemOfUnits}, or {@code null}.
*/
public abstract SystemOfUnitsService getSystemOfUnitsService();
/**
* Returns the service to obtain a {@link UnitFormat}, or {@code null} if none.
*
* @return the service to obtain a {@link UnitFormat}, or {@code null}.
*/
public abstract UnitFormatService getUnitFormatService();
/**
* Return a factory for this {@link Quantity}.
*
* @param quantity
* the quantity
* @return the {@link QuantityFactory}
*/
public abstract > QuantityFactory getQuantityFactory(Class quantity);
/**
* Gets all {@link ServiceProvider}. This method loads the provider when first needed.
*/
private static ServiceProvider[] getProviders() {
ServiceProvider[] p = providers;
if (p == null) {
synchronized (LOCK) {
p = providers;
if (p == null) {
final List loaded = new ArrayList();
for (ServiceProvider provider : ServiceLoader.load(ServiceProvider.class)) {
loaded.add(provider);
}
p = loaded.toArray(new ServiceProvider[loaded.size()]);
Arrays.sort(p, new Comparator() {
@Override
public int compare(ServiceProvider p1, ServiceProvider p2) {
return p2.getPriority() - p1.getPriority();
}
});
providers = p; // Set only on success.
}
}
}
return p;
}
/**
* Returns the list of available service providers.
*
* @return all available service providers.
*/
public static List available() {
return Arrays.asList(getProviders()); // .clone();
}
/**
* Returns the current {@link ServiceProvider}. If necessary the {@link ServiceProvider} will be lazily loaded.
*
* @return the {@link ServiceProvider} used.
* @throws IllegalStateException
* if no {@link ServiceProvider} has been found.
*/
public static ServiceProvider current() {
ServiceProvider[] p = getProviders();
if (p.length != 0) {
return p[0];
}
throw new IllegalStateException("No measurement ServiceProvider found.");
}
/**
* Replaces the current {@link ServiceProvider}.
*
* @param provider
* the new {@link ServiceProvider}
* @return the removed provider, or null.
*/
public static ServiceProvider setCurrent(ServiceProvider provider) {
if (provider == null) {
throw new NullPointerException();
}
synchronized (LOCK) {
ServiceProvider[] p = getProviders();
ServiceProvider old = (p.length != 0) ? p[0] : null;
if (provider != old) {
List copy = new ArrayList(Arrays.asList(p));
copy.remove(provider);
copy.add(0, provider);
providers = copy.toArray(new ServiceProvider[copy.size()]);
// Keep the log inside the synchronized block for making sure that the order
// or logging messages matches the order in which ServiceProviders were set.
Logger.getLogger("javax.measure.spi").log(Level.CONFIG,
(old == null) ? "Measurement ServiceProvider set to {0}" : "Measurement ServiceProvider replaced by {0}", provider.getClass().getName());
}
return old;
}
}
}