reloadableresourcebundlemessagesource.java

一个关于Spring框架的示例应用程序,简单使用,可以参考.

/*
 * Copyright 2002-2004 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
 *
 *      http://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.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Properties;

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.util.DefaultPropertiesPersister;
import org.springframework.util.PropertiesPersister;
import org.springframework.util.StringUtils;

/**
 * MessageSource that accesses the ResourceBundles with the specified basenames.
 * This class uses <code>java.util.Properties</code> instances as its internal
 * data structure for messages, loading them via a PropertiesPersister strategy:
 * The default strategy can load properties files with a specific encoding.
 *
 * <p>In contrast to ResourceBundleMessageSource, this class supports reloading
 * of properties files through the "cacheSeconds" setting, and also through
 * programmatically clearing the properties cache. Since application servers do
 * typically cache all files loaded from the classpath, it is necessary to store
 * resources somewhere else (for example, in the "WEB-INF" directory of a web app).
 * Otherwise changes of files in the classpath are not reflected in the application.
 *
 * <p>Note that the base names set as the "basename" and "basenames" properties are
 * treated in a slightly different fashion than the "basename" 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) will not work in this case.
 *
 * <p>This MessageSource implementation is usually slightly faster than
 * ResourceBundleMessageSource, which builds on <code>java.util.ResourceBundle</code>
 * - in the default mode, i.e. when caching forever. With "cacheSeconds" set to 1,
 * message lookup takes about twice as long - with the benefit that changes in
 * individual properties files are detected with a maximum delay of 1 second.
 * Higher "cacheSeconds" values usually <i>don't</i> make a significant difference.
 *
 * <p>This MessageSource can easily be used outside an ApplicationContext: It uses
 * a DefaultResourceLoader as default, getting overridden with the ApplicationContext
 * 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 org.springframework.util.DefaultPropertiesPersister
 * @see org.springframework.core.io.DefaultResourceLoader
 * @see ResourceBundleMessageSource
 * @see java.util.ResourceBundle
 */
public class ReloadableResourceBundleMessageSource extends AbstractMessageSource
    implements ResourceLoaderAware {

	private static final String PROPERTIES_SUFFIX = ".properties";


	private String[] basenames;

	private String defaultEncoding;

	private Properties fileEncodings;

	private boolean fallbackToSystemLocale = true;

	private long cacheMillis = -1;

	/** Cache to hold filename lists per Locale */
	private final Map cachedFilenames = new HashMap();

	/** Cache to hold already loaded properties per filename */
	private final Map cachedProperties = new HashMap();

	/** Cache to hold merged loaded properties per basename */
	private final Map cachedMergedProperties = new HashMap();

	private PropertiesPersister propertiesPersister = new DefaultPropertiesPersister();

	private ResourceLoader resourceLoader = new DefaultResourceLoader();


	/**
	 * Set a single basename, following the basic ResourceBundle convention of
	 * not specifying file extension or language codes, but in contrast to
	 * ResourceBundleMessageSource referring to a Spring resource location:
	 * e.g. "WEB-INF/messages" for "WEB-INF/messages.properties",
	 * "WEB-INF/messages_en.properties", etc.
	 * @param basename the single basename
	 * @see #setBasenames
	 * @see org.springframework.core.io.ResourceEditor
	 * @see java.util.ResourceBundle
	 */
	public void setBasename(String basename) {
		setBasenames(new String[]{basename});
	}

	/**
	 * Set an array of basenames, each following the above-mentioned special
	 * convention. The associated resource bundles will be checked sequentially
	 * when resolving a message code.
	 * <p>Note that message definitions in a <i>previous</i> resource bundle
	 * will override ones in a later bundle, due to the sequential lookup.
	 * @param basenames an array of basenames
	 * @see #setBasename
	 * @see java.util.ResourceBundle
	 */
	public void setBasenames(String[] basenames) {
		this.basenames = basenames;
	}

	/**
	 * Set the default charset to use for parsing properties files.
	 * Used if no file-specific charset is specified for a file.
	 * <p>Default is none, using java.util.Properties' default charset.
	 * @see #setFileEncodings
	 * @see org.springframework.util.PropertiesPersister#load
	 */
	public void setDefaultEncoding(String defaultEncoding) {
		this.defaultEncoding = defaultEncoding;
	}

	/**
	 * Set per-file charsets to use for parsing properties files.
	 * @param fileEncodings Properties with filenames as keys and charset
	 * names as values. Filenames have to match the basename syntax,
	 * with optional locale-specific appendices: 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;
	}

	/**
	 * Set whether to fall back to the system Locale if no files for a specific
	 * Locale have been found. Default is true; if this is turned off, the only
	 * fallback will be the default file (e.g. "messages.properties" for
	 * basename "messages").
	 * <p>Falling back to the system Locale is the default behavior of
	 * java.util.ResourceBundle. However, this is often not desirable in an
	 * application server environment, where the system Locale is not relevant
	 * to the application at all: Set this flag to "false" in such a scenario.
	 */
	public void setFallbackToSystemLocale(boolean fallbackToSystemLocale) {
		this.fallbackToSystemLocale = fallbackToSystemLocale;
	}

	/**
	 * Set the number of seconds to cache loaded properties files.
	 * <ul>
	 * <li>Default is "-1", indicating to cache forever (just like
	 * java.util.ResourceBundle).
	 * <li>A positive number will cache loaded properties files for the given
	 * number of seconds. This is essentially the interval between refresh attempts.
	 * Note that a refresh attempt will first check the last-modified timestamp
	 * of the file before actually reloading it; so if files don't change, this
	 * interval can be set rather low, as refresh attempts will not actually reload.
	 * <li>A value of "0" will check the last-modified timestamp of the file on
	 * every message access. <b>Do not use this in a production environment!</b>
	 * </ul>
	 */
	public void setCacheSeconds(int cacheSeconds) {
		this.cacheMillis = cacheSeconds * 1000;
	}

	/**
	 * Set the PropertiesPersister to use for parsing properties files.
	 * The default is DefaultPropertiesPersister.
	 * @see org.springframework.util.DefaultPropertiesPersister
	 */
	public void setPropertiesPersister(PropertiesPersister propertiesPersister) {
		this.propertiesPersister = propertiesPersister;
	}

	/**
	 * Set the ResourceLoader to use for loading bundle properties files.
	 * The default is DefaultResourceLoader. Will get overridden by the
	 * ApplicationContext if running in a context.
	 * @see org.springframework.core.io.DefaultResourceLoader
	 */
	public void setResourceLoader(ResourceLoader resourceLoader) {
		this.resourceLoader = resourceLoader;
	}


	protected String resolveCodeWithoutArguments(String code, Locale locale) {
		if (this.cacheMillis < 0) {
			PropertiesHolder propHolder = getMergedProperties(locale);
			String result = propHolder.getProperty(code);
			if (result != null) {
				return result;
			}
		}
		else {
			for (int i = 0; i < this.basenames.length; i++) {
				List filenames = calculateAllFilenames(this.basenames[i], locale);
				for (int j = 0; j < filenames.size(); j++) {
					String filename = (String) filenames.get(j);
					PropertiesHolder propHolder = getProperties(filename);
					String result = propHolder.getProperty(code);
					if (result != null) {
						return result;
					}
				}
			}
		}
		return null;
	}

	protected MessageFormat resolveCode(String code, Locale locale) {
		if (this.cacheMillis < 0) {
			PropertiesHolder propHolder = getMergedProperties(locale);
			MessageFormat result = propHolder.getMessageFormat(code, locale);
			if (result != null) {
				return result;
			}
		}
		else {
			for (int i = 0; i < this.basenames.length; i++) {
				List filenames = calculateAllFilenames(this.basenames[i], locale);
				for (int j = 0; j < filenames.size(); j++) {
					String filename = (String) filenames.get(j);
					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.
	 * <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) {
		synchronized (this.cachedMergedProperties) {
			PropertiesHolder mergedHolder = (PropertiesHolder) this.cachedMergedProperties.get(locale);
			if (mergedHolder != null) {
				return mergedHolder;
			}
			Properties mergedProps = new Properties();