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package gr.uoa.di.driver.util;
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import java.util.concurrent.ScheduledExecutorService;
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import java.util.concurrent.TimeUnit;
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import org.apache.log4j.Logger;
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import eu.dnetlib.api.DriverService;
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/**
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* An implementation of the service locator that keeps a cache of the service
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* and refreshes it periodically.
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*
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* The actual task of service discovery is performed by a locator that is
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* injected.
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*
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* @author <a href="mailto:antleb@di.uoa.gr">Antonis Lempesis</a>
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*
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* @param <S> the service type
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*/
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public class RefreshingServiceLocator<S extends DriverService> implements
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ServiceLocator<S> {
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/** The locator used to discover the service */
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private ServiceLocator<S> locator = null;
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/** the cached instance of the service */
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private S service = null;
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/** the executor that runs the refresh tasks */
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private ScheduledExecutorService executor = null;
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/** the discovery period in milliseconds*/
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private long period = 0;
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@Override
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public synchronized S getService() {
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if (service == null)
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init();
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return service;
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}
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/**
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* Called to initialize the locator. Performs the first service lookup and
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* also schedules the periodic refresh of the cache.
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*
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* */
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private void init() {
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this.service = locator.getService();
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executor.scheduleWithFixedDelay(new RefreshTask(), period, period,
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TimeUnit.MILLISECONDS);
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}
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/**
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* A very simple runnable that refreshed the cache. No synchronization is
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* needed during cache refresh: The old instance will be returned while the
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* locator is working to refresh the cache.
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*
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* @author <a href="mailto:antleb@di.uoa.gr">Antonis Lempesis</a>
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*
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*/
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private class RefreshTask implements Runnable {
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private Logger logger = Logger.getLogger(RefreshTask.class);
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@Override
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public void run() {
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try {
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logger.debug("Refreshing service cache");
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service = locator.getService();
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} catch (Exception e) {
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logger.info("Error refreshing service", e);
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}
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}
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}
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public ServiceLocator<S> getLocator() {
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return locator;
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}
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public void setLocator(ServiceLocator<S> locator) {
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this.locator = locator;
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}
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public ScheduledExecutorService getExecutor() {
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return executor;
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}
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public void setExecutor(ScheduledExecutorService executor) {
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this.executor = executor;
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}
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public long getPeriod() {
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return period;
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}
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public void setPeriod(long period) {
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this.period = period;
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}
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}
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