Spring boot国际化

国际化主要是引入了MessageSource，我们简单看下如何使用，以及其原理。

1.1 设置资源文件

在 properties新建i18n目录

新建message文件：

messages.properties

error.title=Your request cannot be processed

messages_zh_CN.properties

error.title=您的请求无法处理

1.2 配置

修改properties文件的目录：在application.yml或者application.properties中配置 spring.message.basename

spring:
    application:
        name: test-worklog
    messages:
        basename: i18n/messages
        encoding: UTF-8

1.3 使用

引用自动注解的MessageSource,调用messageSource.getMessage即可，注意，需要通过 LocaleContextHolder.getLocale()获取当前的地区。

@Autowired
private MessageSource messageSource;
/**
 * 国际化
 *
 * @param result
 * @return
 */
public String getMessage(String result,Object[] params) {
    String message = "";
    try {
        Locale locale = LocaleContextHolder.getLocale();
        message = messageSource.getMessage(result,params,locale);
    } catch (Exception e) {
        LOGGER.error("parse message error! ",e);
    }
    return message;
}

如何设置个性化的地区呢? forLanguageTag 即可

 Locale locale = Locale.forLanguageTag(user.getLangKey());

1.4 原理分析

MessageSourceAutoConfiguration中，实现了autoconfig

@Configuration
@ConditionalOnMissingBean(value = MessageSource.class,search = SearchStrategy.CURRENT)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Conditional(ResourceBundleCondition.class)
@EnableConfigurationProperties
@ConfigurationProperties(prefix = "spring.messages")
public class MessageSourceAutoConfiguration {

该类一方面读取配置文件，一方面创建了MessageSource的实例:

@Bean
	public MessageSource messageSource() {
		ResourceBundleMessageSource messageSource = new ResourceBundleMessageSource();
		if (StringUtils.hasText(this.basename)) {
			messageSource.setBasenames(StringUtils.commaDelimitedListToStringArray(
					StringUtils.trimAllWhitespace(this.basename)));
		}
		if (this.encoding != null) {
			messageSource.setDefaultEncoding(this.encoding.name());
		}
		messageSource.setFallbackToSystemLocale(this.fallbackToSystemLocale);
		messageSource.setCacheSeconds(this.cacheSeconds);
		messageSource.setAlwaysUseMessageFormat(this.alwaysUseMessageFormat);
		return messageSource;
	}

因此，默认是加载的ResourceBundleMessageSource，该类派生与于AbstractResourceBasedMessageSource

@Override
	public final String getMessage(String code,Object[] args,String defaultMessage,Locale locale) {
		String msg = getMessageInternal(code,args,locale);
		if (msg != null) {
			return msg;
		}
		if (defaultMessage == null) {
			String fallback = getDefaultMessage(code);
			if (fallback != null) {
				return fallback;
			}
		}
		return renderDefaultMessage(defaultMessage,locale);
	}

最终是调用resolveCode来获取message，通过ResourceBundle来获取message

	@Override
	protected MessageFormat resolveCode(String code,Locale locale) {
	    // 遍历语言文件路径
		Set<String> basenames = getBasenameSet();
		for (String basename : basenames) {
			ResourceBundle bundle = getResourceBundle(basename,locale);
			if (bundle != null) {
				MessageFormat messageFormat = getMessageFormat(bundle,code,locale);
				if (messageFormat != null) {
					return messageFormat;
				}
			}
		}
		return null;
	}
	
// 获取ResourceBundle	
protected ResourceBundle getResourceBundle(String basename,Locale locale) {
		if (getCacheMillis() >= 0) {
			// Fresh ResourceBundle.getBundle call in order to let ResourceBundle
			// do its native caching,at the expense of more extensive lookup steps.
			return doGetBundle(basename,locale);
		}
		else {
			// Cache forever: prefer locale cache over repeated getBundle calls.
			synchronized (this.cachedResourceBundles) {
				Map<Locale,ResourceBundle> localeMap = this.cachedResourceBundles.get(basename);
				if (localeMap != null) {
					ResourceBundle bundle = localeMap.get(locale);
					if (bundle != null) {
						return bundle;
					}
				}
				try {
					ResourceBundle bundle = doGetBundle(basename,locale);
					if (localeMap == null) {
						localeMap = new HashMap<Locale,ResourceBundle>();
						this.cachedResourceBundles.put(basename,localeMap);
					}
					localeMap.put(locale,bundle);
					return bundle;
				}
				catch (MissingResourceException ex) {
					if (logger.isWarnEnabled()) {
						logger.warn("ResourceBundle [" + basename + "] not found for MessageSource: " + ex.getMessage());
					}
					// Assume bundle not found
					// -> do NOT throw the exception to allow for checking parent message source.
					return null;
				}
			}
		}
	}

//  ResourceBundle	
protected ResourceBundle doGetBundle(String basename,Locale locale) throws MissingResourceException {
		return ResourceBundle.getBundle(basename,locale,getBundleClassLoader(),new MessageSourceControl());
}

最后来看getMessageFormat：

/**
	 * Return a MessageFormat for the given bundle and code,* fetching already generated MessageFormats from the cache.
	 * @param bundle the ResourceBundle to work on
	 * @param code the message code to retrieve
	 * @param locale the Locale to use to build the MessageFormat
	 * @return the resulting MessageFormat,or {@code null} if no message
	 * defined for the given code
	 * @throws MissingResourceException if thrown by the ResourceBundle
	 */
	protected MessageFormat getMessageFormat(ResourceBundle bundle,String code,Locale locale)
			throws MissingResourceException {

		synchronized (this.cachedBundleMessageFormats) {
		    // 从缓存读取
			Map<String,Map<Locale,MessageFormat>> codeMap = this.cachedBundleMessageFormats.get(bundle);
			Map<Locale,MessageFormat> localeMap = null;
			if (codeMap != null) {
				localeMap = codeMap.get(code);
				if (localeMap != null) {
					MessageFormat result = localeMap.get(locale);
					if (result != null) {
						return result;
					}
				}
			}
	        // 缓存miss，从bundle读取
			String msg = getStringOrNull(bundle,code);
			if (msg != null) {
				if (codeMap == null) {
					codeMap = new HashMap<String,MessageFormat>>();
					this.cachedBundleMessageFormats.put(bundle,codeMap);
				}
				if (localeMap == null) {
					localeMap = new HashMap<Locale,MessageFormat>();
					codeMap.put(code,localeMap);
				}
				MessageFormat result = createMessageFormat(msg,locale);
				localeMap.put(locale,result);
				return result;
			}

			return null;
		}
	}

作者：Jadepeng
出处：jqpeng的技术记事本--http://www.cnblogs.com/xiaoqi
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