https://github.com/spring-projects/spring-framework: Spring Context (Spring IO)
  • Juergen Hoeller 
/*
 * Copyright 2002-2020 the original author or authors.
 *
 * 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
 *
 *      https://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.springframework.context.support;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.text.MessageFormat;
import java.util.ArrayList;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Properties;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.locks.ReentrantLock;

import org.springframework.context.ResourceLoaderAware;
import org.springframework.core.io.DefaultResourceLoader;
import org.springframework.core.io.Resource;
import org.springframework.core.io.ResourceLoader;
import org.springframework.core.io.support.ResourcePropertiesPersister;
import org.springframework.lang.Nullable;
import org.springframework.util.PropertiesPersister;
import org.springframework.util.StringUtils;


Spring-specific MessageSource implementation that accesses resource bundles using specified basenames, participating in the Spring ApplicationContext's resource loading. 
In contrast to the JDK-based ResourceBundleMessageSource, this class uses Properties instances as its custom data structure for messages, loading them via a PropertiesPersister strategy from Spring Resource handles. This strategy is not only capable of reloading files based on timestamp changes, but also of loading properties files with a specific character encoding. It will detect XML property files as well. 
Note that the basenames set as "basenames" property are treated in a slightly different fashion than the "basenames" property of ResourceBundleMessageSource. It follows the basic ResourceBundle rule of not specifying file extension or language codes, but can refer to any Spring resource location (instead of being restricted to classpath resources). With a "classpath:" prefix, resources can still be loaded from the classpath, but "cacheSeconds" values other than "-1" (caching forever) might not work reliably in this case. 
For a typical web application, message files could be placed in WEB-INF: e.g. a "WEB-INF/messages" basename would find a "WEB-INF/messages.properties", "WEB-INF/messages_en.properties" etc arrangement as well as "WEB-INF/messages.xml", "WEB-INF/messages_en.xml" etc. Note that message definitions in a previous
resource bundle will override ones in a later bundle, due to sequential lookup.

This MessageSource can easily be used outside of an ApplicationContext: it will use a DefaultResourceLoader as default, simply getting overridden with the ApplicationContext's resource loader if running in a context. It does not have any other specific dependencies. 
Thanks to Thomas Achleitner for providing the initial implementation of
this message source!

Author:Juergen Hoeller
See Also:
/**
 * Spring-specific {@link org.springframework.context.MessageSource} implementation
 * that accesses resource bundles using specified basenames, participating in the
 * Spring {@link org.springframework.context.ApplicationContext}'s resource loading.
 *
 * <p>In contrast to the JDK-based {@link ResourceBundleMessageSource}, this class uses
 * {@link java.util.Properties} instances as its custom data structure for messages,
 * loading them via a {@link org.springframework.util.PropertiesPersister} strategy
 * from Spring {@link Resource} handles. This strategy is not only capable of
 * reloading files based on timestamp changes, but also of loading properties files
 * with a specific character encoding. It will detect XML property files as well.
 *
 * <p>Note that the basenames set as {@link #setBasenames "basenames"} property
 * are treated in a slightly different fashion than the "basenames" property of
 * {@link ResourceBundleMessageSource}. It follows the basic ResourceBundle rule of not
 * specifying file extension or language codes, but can refer to any Spring resource
 * location (instead of being restricted to classpath resources). With a "classpath:"
 * prefix, resources can still be loaded from the classpath, but "cacheSeconds" values
 * other than "-1" (caching forever) might not work reliably in this case.
 *
 * <p>For a typical web application, message files could be placed in {@code WEB-INF}:
 * e.g. a "WEB-INF/messages" basename would find a "WEB-INF/messages.properties",
 * "WEB-INF/messages_en.properties" etc arrangement as well as "WEB-INF/messages.xml",
 * "WEB-INF/messages_en.xml" etc. Note that message definitions in a <i>previous</i>
 * resource bundle will override ones in a later bundle, due to sequential lookup.

 * <p>This MessageSource can easily be used outside of an
 * {@link org.springframework.context.ApplicationContext}: it will use a
 * {@link org.springframework.core.io.DefaultResourceLoader} as default,
 * simply getting overridden with the ApplicationContext's resource loader
 * if running in a context. It does not have any other specific dependencies.
 *
 * <p>Thanks to Thomas Achleitner for providing the initial implementation of
 * this message source!
 *
 * @author Juergen Hoeller
 * @see #setCacheSeconds
 * @see #setBasenames
 * @see #setDefaultEncoding
 * @see #setFileEncodings
 * @see #setPropertiesPersister
 * @see #setResourceLoader
 * @see ResourcePropertiesPersister
 * @see org.springframework.core.io.DefaultResourceLoader
 * @see ResourceBundleMessageSource
 * @see java.util.ResourceBundle
 */
public class ReloadableResourceBundleMessageSource extends AbstractResourceBasedMessageSource
		implements ResourceLoaderAware {

	private static final String PROPERTIES_SUFFIX = ".properties";

	private static final String XML_SUFFIX = ".xml";


	@Nullable
	private Properties fileEncodings;

	private boolean concurrentRefresh = true;

	private PropertiesPersister propertiesPersister = ResourcePropertiesPersister.INSTANCE;

	private ResourceLoader resourceLoader = new DefaultResourceLoader();

	// Cache to hold filename lists per Locale
	private final ConcurrentMap<String, Map<Locale, List<String>>> cachedFilenames = new ConcurrentHashMap<>();

	// Cache to hold already loaded properties per filename
	private final ConcurrentMap<String, PropertiesHolder> cachedProperties = new ConcurrentHashMap<>();

	// Cache to hold already loaded properties per filename
	private final ConcurrentMap<Locale, PropertiesHolder> cachedMergedProperties = new ConcurrentHashMap<>();


	
Set per-file charsets to use for parsing properties files.

Only applies to classic properties files, not to XML files.

Params:
  • fileEncodings – a Properties with filenames as keys and charset
names as values. Filenames have to match the basename syntax,
with optional locale-specific components: e.g. "WEB-INF/messages"
or "WEB-INF/messages_en".
See Also:
/**
	 * Set per-file charsets to use for parsing properties files.
	 * <p>Only applies to classic properties files, not to XML files.
	 * @param fileEncodings a Properties with filenames as keys and charset
	 * names as values. Filenames have to match the basename syntax,
	 * with optional locale-specific components: e.g. "WEB-INF/messages"
	 * or "WEB-INF/messages_en".
	 * @see #setBasenames
	 * @see org.springframework.util.PropertiesPersister#load
	 */
	public void setFileEncodings(Properties fileEncodings) {
		this.fileEncodings = fileEncodings;
	}

	
Specify whether to allow for concurrent refresh behavior, i.e. one thread
locked in a refresh attempt for a specific cached properties file whereas
other threads keep returning the old properties for the time being, until
the refresh attempt has completed.

Default is "true": this behavior is new as of Spring Framework 4.1,
minimizing contention between threads. If you prefer the old behavior,
i.e. to fully block on refresh, switch this flag to "false".

See Also:
Since:4.1
/**
	 * Specify whether to allow for concurrent refresh behavior, i.e. one thread
	 * locked in a refresh attempt for a specific cached properties file whereas
	 * other threads keep returning the old properties for the time being, until
	 * the refresh attempt has completed.
	 * <p>Default is "true": this behavior is new as of Spring Framework 4.1,
	 * minimizing contention between threads. If you prefer the old behavior,
	 * i.e. to fully block on refresh, switch this flag to "false".
	 * @since 4.1
	 * @see #setCacheSeconds
	 */
	public void setConcurrentRefresh(boolean concurrentRefresh) {
		this.concurrentRefresh = concurrentRefresh;
	}

	
Set the PropertiesPersister to use for parsing properties files.

The default is ResourcePropertiesPersister.

See Also:
  • INSTANCE.INSTANCE
/**
	 * Set the PropertiesPersister to use for parsing properties files.
	 * <p>The default is ResourcePropertiesPersister.
	 * @see ResourcePropertiesPersister#INSTANCE
	 */
	public void setPropertiesPersister(@Nullable PropertiesPersister propertiesPersister) {
		this.propertiesPersister =
				(propertiesPersister != null ? propertiesPersister : ResourcePropertiesPersister.INSTANCE);
	}

	
Set the ResourceLoader to use for loading bundle properties files.

The default is a DefaultResourceLoader. Will get overridden by the
ApplicationContext if running in a context, as it implements the
ResourceLoaderAware interface. Can be manually overridden when
running outside of an ApplicationContext.

See Also:
/**
	 * Set the ResourceLoader to use for loading bundle properties files.
	 * <p>The default is a DefaultResourceLoader. Will get overridden by the
	 * ApplicationContext if running in a context, as it implements the
	 * ResourceLoaderAware interface. Can be manually overridden when
	 * running outside of an ApplicationContext.
	 * @see org.springframework.core.io.DefaultResourceLoader
	 * @see org.springframework.context.ResourceLoaderAware
	 */
	@Override
	public void setResourceLoader(@Nullable ResourceLoader resourceLoader) {
		this.resourceLoader = (resourceLoader != null ? resourceLoader : new DefaultResourceLoader());
	}


	
Resolves the given message code as key in the retrieved bundle files,
returning the value found in the bundle as-is (without MessageFormat parsing).

/**
	 * Resolves the given message code as key in the retrieved bundle files,
	 * returning the value found in the bundle as-is (without MessageFormat parsing).
	 */
	@Override
	protected String resolveCodeWithoutArguments(String code, Locale locale) {
		if (getCacheMillis() < 0) {
			PropertiesHolder propHolder = getMergedProperties(locale);
			String result = propHolder.getProperty(code);
			if (result != null) {
				return result;
			}
		}
		else {
			for (String basename : getBasenameSet()) {
				List<String> filenames = calculateAllFilenames(basename, locale);
				for (String filename : filenames) {
					PropertiesHolder propHolder = getProperties(filename);
					String result = propHolder.getProperty(code);
					if (result != null) {
						return result;
					}
				}
			}
		}
		return null;
	}

	
Resolves the given message code as key in the retrieved bundle files,
using a cached MessageFormat instance per message code.

/**
	 * Resolves the given message code as key in the retrieved bundle files,
	 * using a cached MessageFormat instance per message code.
	 */
	@Override
	@Nullable
	protected MessageFormat resolveCode(String code, Locale locale) {
		if (getCacheMillis() < 0) {
			PropertiesHolder propHolder = getMergedProperties(locale);
			MessageFormat result = propHolder.getMessageFormat(code, locale);
			if (result != null) {
				return result;
			}
		}
		else {
			for (String basename : getBasenameSet()) {
				List<String> filenames = calculateAllFilenames(basename, locale);
				for (String filename : filenames) {
					PropertiesHolder propHolder = getProperties(filename);
					MessageFormat result = propHolder.getMessageFormat(code, locale);
					if (result != null) {
						return result;
					}
				}
			}
		}
		return null;
	}


	
Get a PropertiesHolder that contains the actually visible properties
for a Locale, after merging all specified resource bundles.
Either fetches the holder from the cache or freshly loads it.

Only used when caching resource bundle contents forever, i.e.
with cacheSeconds < 0. Therefore, merged properties are always
cached forever.

/**
	 * Get a PropertiesHolder that contains the actually visible properties
	 * for a Locale, after merging all specified resource bundles.
	 * Either fetches the holder from the cache or freshly loads it.
	 * <p>Only used when caching resource bundle contents forever, i.e.
	 * with cacheSeconds < 0. Therefore, merged properties are always
	 * cached forever.
	 */
	protected PropertiesHolder getMergedProperties(Locale locale) {
		PropertiesHolder mergedHolder = this.cachedMergedProperties.get(locale);
		if (mergedHolder != null) {
			return mergedHolder;
		}

		Properties mergedProps = newProperties();
		long latestTimestamp = -1;
		String[] basenames = StringUtils.toStringArray(getBasenameSet());
		for (int i = basenames.length - 1; i >= 0; i--) {
			List<String> filenames = calculateAllFilenames(basenames[i], locale);
			for (int j = filenames.size() - 1; j >= 0; j--) {
				String filename = filenames.get(j);
				PropertiesHolder propHolder = getProperties(filename);
				if (propHolder.getProperties() != null) {
					mergedProps.putAll(propHolder.getProperties());
					if (propHolder.getFileTimestamp() > latestTimestamp) {
						latestTimestamp = propHolder.getFileTimestamp();
					}
				}
			}
		}

		mergedHolder = new PropertiesHolder(mergedProps, latestTimestamp);
		PropertiesHolder existing = this.cachedMergedProperties.putIfAbsent(locale, mergedHolder);
		if (existing != null) {
			mergedHolder = existing;
		}
		return mergedHolder;
	}

	
Calculate all filenames for the given bundle basename and Locale.
Will calculate filenames for the given Locale, the system Locale
(if applicable), and the default file.

Params:
  • basename – the basename of the bundle
  • locale – the locale
See Also:
Returns:the List of filenames to check
/**
	 * Calculate all filenames for the given bundle basename and Locale.
	 * Will calculate filenames for the given Locale, the system Locale
	 * (if applicable), and the default file.
	 * @param basename the basename of the bundle
	 * @param locale the locale
	 * @return the List of filenames to check
	 * @see #setFallbackToSystemLocale
	 * @see #calculateFilenamesForLocale
	 */
	protected List<String> calculateAllFilenames(String basename, Locale locale) {
		Map<Locale, List<String>> localeMap = this.cachedFilenames.get(basename);
		if (localeMap != null) {
			List<String> filenames = localeMap.get(locale);
			if (filenames != null) {
				return filenames;
			}
		}

		// Filenames for given Locale
		List<String> filenames = new ArrayList<>(7);
		filenames.addAll(calculateFilenamesForLocale(basename, locale));

		// Filenames for default Locale, if any
		Locale defaultLocale = getDefaultLocale();
		if (defaultLocale != null && !defaultLocale.equals(locale)) {
			List<String> fallbackFilenames = calculateFilenamesForLocale(basename, defaultLocale);
			for (String fallbackFilename : fallbackFilenames) {
				if (!filenames.contains(fallbackFilename)) {
					// Entry for fallback locale that isn't already in filenames list.
					filenames.add(fallbackFilename);
				}
			}
		}

		// Filename for default bundle file
		filenames.add(basename);

		if (localeMap == null) {
			localeMap = new ConcurrentHashMap<>();
			Map<Locale, List<String>> existing = this.cachedFilenames.putIfAbsent(basename, localeMap);
			if (existing != null) {
				localeMap = existing;
			}
		}
		localeMap.put(locale, filenames);
		return filenames;
	}

	
Calculate the filenames for the given bundle basename and Locale,
appending language code, country code, and variant code.
E.g.: basename "messages", Locale "de_AT_oo" -> "messages_de_AT_OO",
"messages_de_AT", "messages_de".

Follows the rules defined by Locale.toString(). 
Params:
  • basename – the basename of the bundle
  • locale – the locale
Returns:the List of filenames to check
/**
	 * Calculate the filenames for the given bundle basename and Locale,
	 * appending language code, country code, and variant code.
	 * E.g.: basename "messages", Locale "de_AT_oo" -> "messages_de_AT_OO",
	 * "messages_de_AT", "messages_de".
	 * <p>Follows the rules defined by {@link java.util.Locale#toString()}.
	 * @param basename the basename of the bundle
	 * @param locale the locale
	 * @return the List of filenames to check
	 */
	protected List<String> calculateFilenamesForLocale(String basename, Locale locale) {
		List<String> result = new ArrayList<>(3);
		String language = locale.getLanguage();
		String country = locale.getCountry();
		String variant = locale.getVariant();
		StringBuilder temp = new StringBuilder(basename);

		temp.append('_');
		if (language.length() > 0) {
			temp.append(language);
			result.add(0, temp.toString());
		}

		temp.append('_');
		if (country.length() > 0) {
			temp.append(country);
			result.add(0, temp.toString());
		}

		if (variant.length() > 0 && (language.length() > 0 || country.length() > 0)) {
			temp.append('_').append(variant);
			result.add(0, temp.toString());
		}

		return result;
	}


	
Get a PropertiesHolder for the given filename, either from the
cache or freshly loaded.

Params:
  • filename – the bundle filename (basename + Locale)
Returns:the current PropertiesHolder for the bundle
/**
	 * Get a PropertiesHolder for the given filename, either from the
	 * cache or freshly loaded.
	 * @param filename the bundle filename (basename + Locale)
	 * @return the current PropertiesHolder for the bundle
	 */
	protected PropertiesHolder getProperties(String filename) {
		PropertiesHolder propHolder = this.cachedProperties.get(filename);
		long originalTimestamp = -2;

		if (propHolder != null) {
			originalTimestamp = propHolder.getRefreshTimestamp();
			if (originalTimestamp == -1 || originalTimestamp > System.currentTimeMillis() - getCacheMillis()) {
				// Up to date
				return propHolder;
			}
		}
		else {
			propHolder = new PropertiesHolder();
			PropertiesHolder existingHolder = this.cachedProperties.putIfAbsent(filename, propHolder);
			if (existingHolder != null) {
				propHolder = existingHolder;
			}
		}

		// At this point, we need to refresh...
		if (this.concurrentRefresh && propHolder.getRefreshTimestamp() >= 0) {
			// A populated but stale holder -> could keep using it.
			if (!propHolder.refreshLock.tryLock()) {
				// Getting refreshed by another thread already ->
				// let's return the existing properties for the time being.
				return propHolder;
			}
		}
		else {
			propHolder.refreshLock.lock();
		}
		try {
			PropertiesHolder existingHolder = this.cachedProperties.get(filename);
			if (existingHolder != null && existingHolder.getRefreshTimestamp() > originalTimestamp) {
				return existingHolder;
			}
			return refreshProperties(filename, propHolder);
		}
		finally {
			propHolder.refreshLock.unlock();
		}
	}

	
Refresh the PropertiesHolder for the given bundle filename. The holder can be null if not cached before, or a timed-out cache entry (potentially getting re-validated against the current last-modified timestamp). 
Params:
  • filename – the bundle filename (basename + Locale)
  • propHolder – the current PropertiesHolder for the bundle
/**
	 * Refresh the PropertiesHolder for the given bundle filename.
	 * The holder can be {@code null} if not cached before, or a timed-out cache entry
	 * (potentially getting re-validated against the current last-modified timestamp).
	 * @param filename the bundle filename (basename + Locale)
	 * @param propHolder the current PropertiesHolder for the bundle
	 */
	protected PropertiesHolder refreshProperties(String filename, @Nullable PropertiesHolder propHolder) {
		long refreshTimestamp = (getCacheMillis() < 0 ? -1 : System.currentTimeMillis());

		Resource resource = this.resourceLoader.getResource(filename + PROPERTIES_SUFFIX);
		if (!resource.exists()) {
			resource = this.resourceLoader.getResource(filename + XML_SUFFIX);
		}

		if (resource.exists()) {
			long fileTimestamp = -1;
			if (getCacheMillis() >= 0) {
				// Last-modified timestamp of file will just be read if caching with timeout.
				try {
					fileTimestamp = resource.lastModified();
					if (propHolder != null && propHolder.getFileTimestamp() == fileTimestamp) {
						if (logger.isDebugEnabled()) {
							logger.debug("Re-caching properties for filename [" + filename + "] - file hasn't been modified");
						}
						propHolder.setRefreshTimestamp(refreshTimestamp);
						return propHolder;
					}
				}
				catch (IOException ex) {
					// Probably a class path resource: cache it forever.
					if (logger.isDebugEnabled()) {
						logger.debug(resource + " could not be resolved in the file system - assuming that it hasn't changed", ex);
					}
					fileTimestamp = -1;
				}
			}
			try {
				Properties props = loadProperties(resource, filename);
				propHolder = new PropertiesHolder(props, fileTimestamp);
			}
			catch (IOException ex) {
				if (logger.isWarnEnabled()) {
					logger.warn("Could not parse properties file [" + resource.getFilename() + "]", ex);
				}
				// Empty holder representing "not valid".
				propHolder = new PropertiesHolder();
			}
		}

		else {
			// Resource does not exist.
			if (logger.isDebugEnabled()) {
				logger.debug("No properties file found for [" + filename + "] - neither plain properties nor XML");
			}
			// Empty holder representing "not found".
			propHolder = new PropertiesHolder();
		}

		propHolder.setRefreshTimestamp(refreshTimestamp);
		this.cachedProperties.put(filename, propHolder);
		return propHolder;
	}

	
Load the properties from the given resource.

Params:
  • resource – the resource to load from
  • filename – the original bundle filename (basename + Locale)
Throws:
Returns:the populated Properties instance
/**
	 * Load the properties from the given resource.
	 * @param resource the resource to load from
	 * @param filename the original bundle filename (basename + Locale)
	 * @return the populated Properties instance
	 * @throws IOException if properties loading failed
	 */
	protected Properties loadProperties(Resource resource, String filename) throws IOException {
		Properties props = newProperties();
		try (InputStream is = resource.getInputStream()) {
			String resourceFilename = resource.getFilename();
			if (resourceFilename != null && resourceFilename.endsWith(XML_SUFFIX)) {
				if (logger.isDebugEnabled()) {
					logger.debug("Loading properties [" + resource.getFilename() + "]");
				}
				this.propertiesPersister.loadFromXml(props, is);
			}
			else {
				String encoding = null;
				if (this.fileEncodings != null) {
					encoding = this.fileEncodings.getProperty(filename);
				}
				if (encoding == null) {
					encoding = getDefaultEncoding();
				}
				if (encoding != null) {
					if (logger.isDebugEnabled()) {
						logger.debug("Loading properties [" + resource.getFilename() + "] with encoding '" + encoding + "'");
					}
					this.propertiesPersister.load(props, new InputStreamReader(is, encoding));
				}
				else {
					if (logger.isDebugEnabled()) {
						logger.debug("Loading properties [" + resource.getFilename() + "]");
					}
					this.propertiesPersister.load(props, is);
				}
			}
			return props;
		}
	}

	
Template method for creating a plain new Properties instance. The default implementation simply calls Properties(). 
Allows for returning a custom Properties extension in subclasses. Overriding methods should just instantiate a custom Properties subclass, with no further initialization or population to be performed at that point. 
Returns:a plain Properties instance
Since:4.2
/**
	 * Template method for creating a plain new {@link Properties} instance.
	 * The default implementation simply calls {@link Properties#Properties()}.
	 * <p>Allows for returning a custom {@link Properties} extension in subclasses.
	 * Overriding methods should just instantiate a custom {@link Properties} subclass,
	 * with no further initialization or population to be performed at that point.
	 * @return a plain Properties instance
	 * @since 4.2
	 */
	protected Properties newProperties() {
		return new Properties();
	}


	
Clear the resource bundle cache.
Subsequent resolve calls will lead to reloading of the properties files.

/**
	 * Clear the resource bundle cache.
	 * Subsequent resolve calls will lead to reloading of the properties files.
	 */
	public void clearCache() {
		logger.debug("Clearing entire resource bundle cache");
		this.cachedProperties.clear();
		this.cachedMergedProperties.clear();
	}

	
Clear the resource bundle caches of this MessageSource and all its ancestors.

See Also:
  • clearCache
/**
	 * Clear the resource bundle caches of this MessageSource and all its ancestors.
	 * @see #clearCache
	 */
	public void clearCacheIncludingAncestors() {
		clearCache();
		if (getParentMessageSource() instanceof ReloadableResourceBundleMessageSource) {
			((ReloadableResourceBundleMessageSource) getParentMessageSource()).clearCacheIncludingAncestors();
		}
	}


	@Override
	public String toString() {
		return getClass().getName() + ": basenames=" + getBasenameSet();
	}


	
PropertiesHolder for caching.
Stores the last-modified timestamp of the source file for efficient
change detection, and the timestamp of the last refresh attempt
(updated every time the cache entry gets re-validated).

/**
	 * PropertiesHolder for caching.
	 * Stores the last-modified timestamp of the source file for efficient
	 * change detection, and the timestamp of the last refresh attempt
	 * (updated every time the cache entry gets re-validated).
	 */
	protected class PropertiesHolder {

		@Nullable
		private final Properties properties;

		private final long fileTimestamp;

		private volatile long refreshTimestamp = -2;

		private final ReentrantLock refreshLock = new ReentrantLock();

		
Cache to hold already generated MessageFormats per message code. 
/** Cache to hold already generated MessageFormats per message code. */
		private final ConcurrentMap<String, Map<Locale, MessageFormat>> cachedMessageFormats =
				new ConcurrentHashMap<>();

		public PropertiesHolder() {
			this.properties = null;
			this.fileTimestamp = -1;
		}

		public PropertiesHolder(Properties properties, long fileTimestamp) {
			this.properties = properties;
			this.fileTimestamp = fileTimestamp;
		}

		@Nullable
		public Properties getProperties() {
			return this.properties;
		}

		public long getFileTimestamp() {
			return this.fileTimestamp;
		}

		public void setRefreshTimestamp(long refreshTimestamp) {
			this.refreshTimestamp = refreshTimestamp;
		}

		public long getRefreshTimestamp() {
			return this.refreshTimestamp;
		}

		@Nullable
		public String getProperty(String code) {
			if (this.properties == null) {
				return null;
			}
			return this.properties.getProperty(code);
		}

		@Nullable
		public MessageFormat getMessageFormat(String code, Locale locale) {
			if (this.properties == null) {
				return null;
			}
			Map<Locale, MessageFormat> localeMap = this.cachedMessageFormats.get(code);
			if (localeMap != null) {
				MessageFormat result = localeMap.get(locale);
				if (result != null) {
					return result;
				}
			}
			String msg = this.properties.getProperty(code);
			if (msg != null) {
				if (localeMap == null) {
					localeMap = new ConcurrentHashMap<>();
					Map<Locale, MessageFormat> existing = this.cachedMessageFormats.putIfAbsent(code, localeMap);
					if (existing != null) {
						localeMap = existing;
					}
				}
				MessageFormat result = createMessageFormat(msg, locale);
				localeMap.put(locale, result);
				return result;
			}
			return null;
		}
	}

}