FromFileConfigurationLoadingStrategy.java

package org.dcache.gplazma.configuration;

import java.io.File;
import java.util.concurrent.TimeUnit;

import org.dcache.gplazma.configuration.parser.ConfigurationParser;
import org.dcache.gplazma.configuration.parser.ConfigurationParserFactory;
import org.dcache.gplazma.configuration.parser.FactoryConfigurationException;
import org.dcache.gplazma.configuration.parser.ParseException;

/**
 * This loading strategy loads the configuration from file, if file has been
 * updated.
 * This class is not thread safe.
 * @author timur
 */
public class FromFileConfigurationLoadingStrategy
        implements  ConfigurationLoadingStrategy
{
    private static final long CONFIGURATION_UPDATE_FREQUENCY_MILLIS =
            TimeUnit.SECONDS.toMillis(1);

    private final File configurationFile;
    private long configurationFileLastModified;
    private long configurationFileLastChecked;

    public FromFileConfigurationLoadingStrategy(File configurationFile)
    {
        this.configurationFile = configurationFile;
    }

    public FromFileConfigurationLoadingStrategy(String configurationFileName)
    {
        this(new File(configurationFileName));
    }

    /**
     *
     * @return true if the configuration file has been modified,
     *   false otherwise
     */
    @Override
    public boolean hasUpdated()
    {
        if( (System.currentTimeMillis() - configurationFileLastChecked) <
                CONFIGURATION_UPDATE_FREQUENCY_MILLIS) {
            /* we checked less then CONFIGURATION_UPDATE_FREQUNCY_MILLIS
             * milliseconds ago */
            return false;
        }
        if(configurationFileLastModified == configurationFile.lastModified() ) {
            //configuration file has not been updated. no need to reread
            return false;
        }
        return true;
     }

    /**
     *
     * @return configuration loaded from the configuration file
     */
    @Override
    public Configuration load() throws ParseException,
            FactoryConfigurationException
    {
        configurationFileLastModified =  configurationFile.lastModified();
        configurationFileLastChecked = System.currentTimeMillis();
        ConfigurationParserFactory parserFactory =
                ConfigurationParserFactory.getInstance();
        ConfigurationParser parser = parserFactory.newConfigurationParser();
        return parser.parse(configurationFile);
    }
}