在 Spring MVC 中动态生成可用语言列表

Question

我已经在 Spring MVC 3 中设置了 i18n，并且它工作正常。 有几个文件，每个文件都有自己的语言：messages_en.properties、messages_de.properties 等。

在我的一个 JSP 中，我需要向用户显示包含所有可用语言的组合，并且我希望此列表是动态的，即从服务器中现有的语言文件即时生成。

是否有任何内置方法可以生成此列表？或者我是否必须检查语言文件所在的文件夹并解析它们？

谢谢！

纳乔

Answer 1

如何将其放入可以访问 ReloadableResourceBundleMessageSource 的内容中？

ReloadableResourceBundleMessageSource rrbms = getMessageSource();   
final String defaultMessage = "NOT FOUND";
List<Locale> availableLocales = new ArrayList<Locale>();
for (Locale locale : Locale.getAvailableLocales()) {
    String msg = rrbms.getMessage("test.code", null, defaultMessage, locale);
    if (!defaultMessage.equals(msg)) {
       availableLocales.add(locale);
    }
}

只需确保每种受支持的语言提供 test.code 值即可。

Answer 2

想法如下：在 .properties 文件中创建 test 变量，该变量的内容必须是 ISO 国家名称（2 个符号，例如：Russia=RU）。对于默认区域设置，您可以设置 test=DEFAUL。
文件夹结构和资源包内容：

{
    public static void main(String[] args) {
        Locale[] availableLocales = Locale.getAvailableLocales();
        List<Locale> existingLocales = new ArrayList<>();
        existingLocales.add(Locale.getDefault());

        for (Locale value : availableLocales) {
            if (isLocaleExist(value)) {
                existingLocales.add(value);
            }
        }

        for (Locale value : existingLocales) {
            System.out.println(value);
        }
    }

    public static boolean isLocaleExist(Locale locale) {
        ResourceBundle bundle = ResourceBundle.getBundle("languages.but", locale);
        final String value = bundle.getString("test");
        return value.equals(locale.getCountry());
    }
}

代码结果：

Answer 3

这将是一个很好的功能，但我认为您不会找到内置方法，因为属性文件的“失败”机制意味着拥有 messages_de.properties 不会必然意味着每条消息都有德语版本。所以 Spring 无法构建一个很好的 Map 来从中获取密钥。

不过，您应该能够使用 Spring 来使您的工作变得更轻松，而不必自己访问文件系统：

• 从 Spring 的 ResourceBundle ClassLoader 中获取ResourceBundleMessageSource
• 使用该ClassLoader来列出所有“消息”资源：

Enumeration; allMsgs = bundleClassLoader.findResources("messages");

• 然后迭代 Enumeration，获取语言环境（en、de 等） ) 来自每个 URL 的部分

Answer 4

好的，找到了两个解决方案。对于两者，假设它们在 Spring MVC @Controller 注解的类中执行。每个都会生成一个 HashMap (languages)，其中键是 2 个字母的 ISO 语言代码，值是语言名称（在当前区域设置中，在这些示例中是一个名为 < code>HSConstants.currentLocale)

1.- 由 @millhouse 提交的（见上文/下文），经过一些调整后即可工作：

    HashMap languages = new HashMap();  
    final String defaultMessage = "NOT FOUND";  
    HashMap availableLocales = new HashMap();  
    for (Locale locale : Locale.getAvailableLocales()) {  
        String msg = rrbms.getMessage("currentLanguage", null, defaultMessage, locale);  
        if (!defaultMessage.equals(msg) && !availableLocales.containsKey(locale.getLanguage())){  
            availableLocales.put(locale.getLanguage(), locale);  
        }  
    }  
    for (String c : availableLocales.keySet()){  
        languages.put(c, availableLocales.get(c).getDisplayLanguage(HSConstants.currentLocale));  
    }  
    model.addAttribute("languages", languages);  

此解决方案要求在每种语言 .properties 文件中设置带有语言的条目（在上面的示例中，它将是“currentLanguage”）。例如，在 messages_it.properties 中，必须有这样的条目： currentLanguage=Italiano

2.- 原始方法，即直接访问文件夹/文件：假设文件语言位于 /WEB-INF/languages 中，并且具有基本名称fr-messages：

HashMap languages = new HashMap();  
String languagesFolderPath = request.getSession().getServletContext().getRealPath("/WEB-INF/languages");  
File folder = new File(languagesFolderPath);  
File[] listOfFiles = folder.listFiles();  

for (int i = 0; i < listOfFiles.length; i++){  
   String fileName = listOfFiles[i].getName();  
   if (fileName.startsWith("fr-messages_") && fileName.endsWith(".properties")){  
      // Extract the language code, which is between the underscore and the .properties extension  
      String language = fileName.substring(12, fileName.indexOf(".properties"));  
      Locale l = new Locale(language);  
      languages.put(language, l.getDisplayLanguage(HSConstants.currentLocale));  
   }  
}  
model.addAttribute("languages", languages);  

然后，在您的 JSP 中，使用 languages 映射呈现选择框：

<select name="language">
    <c:forEach items="${languages}" var="language">
        <c:choose>
            <c:when test="${platform.language == language.key}">
                <option value="${language.key}" selected="SELECTED">${language.value}</option>
            </c:when>
            <c:otherwise>
                <option value="${language.key}">${language.value}</option>
            </c:otherwise>
        </c:choose>                         
    </c:forEach>
</select>

Answer 5

我想与大家分享我的解决方案。

当前问题的经过验证的响应（具有两个解决方案）确实很有趣。
第一个解决方案的唯一问题是使用硬编码消息键（“currentLanguage”），该键可能会从相应的属性文件中消失。
第二个需要对属性文件的基本名称（“fr-messages_”）进行硬编码。但文件名可以更改...

因此，我按照经过验证的响应的示例来扩展我的自定义 ResourceBundleMessageSource 来执行此操作。

最初，我需要获取 Spring 消息属性文件的内容（messages_en.properties、messages_fr.properties，...），因为我有一个完整的 Javascript 前端（使用 ExtJ）。因此，我需要在 JS 对象上加载应用程序的所有（国际化）标签。
但它不存在......出于这个原因，我开发了一个自定义的ReloadableResourceBundleMessageSource类。相应的方法是“getAllProperties()”、“getAllPropertiesAsMap()”和“getAllPropertiesAsMessages()”。

后来，我需要获取应用程序上可用的区域设置。阅读此 stackoverflow 页面后，我想到了扩展我的 ReloadableResourceBundleMessageSource 类来做到这一点。您可以看到“getAvailableLocales()”和“isAvailableLocale()”（仅测试一种区域设置）方法。

package fr.ina.archibald.web.support;

import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Properties;
import java.util.Set;

import org.apache.commons.io.FilenameUtils;
import org.apache.commons.lang3.LocaleUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.core.io.Resource;
import org.springframework.core.io.ResourceLoader;
import org.springframework.util.ReflectionUtils;

import fr.ina.archibald.commons.util.StringUtils;
import fr.ina.archibald.entity.MessageEntity;

/**
 * Custom {@link org.springframework.context.support.ReloadableResourceBundleMessageSource}.
 * 
 * @author srambeau
 */
public class ReloadableResourceBundleMessageSource extends org.springframework.context.support.ReloadableResourceBundleMessageSource {

    private static final Logger LOGGER = LoggerFactory.getLogger(ReloadableResourceBundleMessageSource.class);

    private static final String PROPERTIES_SUFFIX = ".properties";

    private static final String XML_SUFFIX = ".xml";

    private Set<Locale> cacheAvailableLocales;

    private Set<Resource> cacheResources;

    /**
     * Returns all messages for the specified {@code Locale}.
     * 
     * @param locale the {@code Locale}.
     * 
     * @return a {@code Properties} containing all the expected messages or {@code null} if the {@code locale} argument is null or if the properties are empty.
     */
    public Properties getAllProperties(final Locale locale) {
        if(locale == null) {
            LOGGER.debug("Cannot get all properties. 'locale' argument is null.");
            return null;
        }
        return getMergedProperties(locale).getProperties();
    }

    /**
     * Returns all messages for the specified {@code Locale}.
     * 
     * @param locale the {@code Locale}.
     * 
     * @return a {@code Map} containing all the expected messages or {@code null} if the {@code locale} argument is null or if the properties are empty.
     */
    @SuppressWarnings({ "unchecked", "rawtypes" })
    public Map<String, String> getAllPropertiesAsMap(final Locale locale) {
        if(locale == null) {
            LOGGER.debug("Cannot get all properties as Map. 'locale' argument is null.");
            return null;
        }
        Properties props = getAllProperties(locale);
        if(props == null) {
            LOGGER.debug("Cannot get all properties as Map. The properties are missing.");
            return null;
        }
        return new HashMap<String, String>((Map) props);
    }

    /**
     * Returns all messages for the specified {@code Locale}.
     * 
     * @param locale the {@code Locale}.
     * 
     * @return a {@code List<MessageEntity>} containing all the expected messages or {@code null} if the {@code locale} argument is null or if the properties are empty.
     */
    public List<MessageEntity> getAllPropertiesAsMessages(final Locale locale) {
        if(locale == null) {
            LOGGER.debug("Cannot get all properties as MessageEntity. 'locale' argument is null.");
            return null;
        }
        Properties props = getAllProperties(locale);
        if(props == null) {
            LOGGER.debug("Cannot get all properties as MessageEntity. The properties are missing.");
            return null;
        }
        Set<Entry<Object, Object>> propsSet = props.entrySet();
        List<MessageEntity> messages = new ArrayList<MessageEntity>();
        for(Entry<Object, Object> prop : propsSet) {
            messages.add(new MessageEntity((String) prop.getKey(), (String) prop.getValue()));
        }
        return messages;
    }

    /**
     * Returns the available {@code Locales} on the specified application context. Calculated from the Spring message files of the application context.
     * <p>
     * Example of Locales returned corresponding with the messages files defines on the application:
     * 
     * <pre>
     * messages_en.properties                         --> en
     * messages_fr.properties                         --> fr
     * messages_en.properties, messages_fr.properties --> en, fr
     * </pre>
     * </p>
     * 
     * @return the set of {@code Locales} or null if an error occurs.
     */
    public Set<Locale> getAvailableLocales() {
        if(cacheAvailableLocales != null) {
            return cacheAvailableLocales;
        }
        cacheAvailableLocales = getLocales(getAllFileNames(), getMessageFilePrefixes());
        return cacheAvailableLocales;
    }

    /**
     * Indicates if the specified {@code Locale} is available on the application.
     * <p>
     * Examples of results returned if the application contains the files "messages_en.properties" and "messages_fr.properties":
     * 
     * <pre>
     * en --> true
     * fr --> true
     * de --> false
     * es --> false
     * </pre>
     * 
     * @param locale the {@code Locale}.
     * 
     * @return {@code true} if the locale is available, {@code false} otherwise.
     */
    public boolean isAvailableLocale(final Locale locale) {
        Set<Locale> locales = getAvailableLocales();
        if(locales == null) {
            return false;
        }
        return locales.contains(locale);
    }

    // ********************** PRIVATE METHODES **********************

    /**
     * Returns the {@code Locales} specified on the file names.
     * 
     * @param fileNames the file names.
     * @param filePrefixes the basenames' prefixes of the resources bundles.
     * 
     * @return the set of the {@code Locales}.
     */
    private Set<Locale> getLocales(final List<String> fileNames, List<String> filePrefixes) {
        if(fileNames == null || fileNames.isEmpty() || filePrefixes == null || filePrefixes.isEmpty()) {
            LOGGER.debug("Cannot get available Locales. fileNames=[" + StringUtils.toString(fileNames) + "], filePrefixes=[" + StringUtils.toString(filePrefixes) + "]");
            return null;
        }
        Set<Locale> locales = new HashSet<Locale>();
        for(String fileName : fileNames) {
            String fileNameWithoutExtension = FilenameUtils.getBaseName(fileName);
            for(String filePrefixe : filePrefixes) {
                String localeStr = fileNameWithoutExtension.substring(filePrefixe.length() + 1);
                try {
                    locales.add(LocaleUtils.toLocale(localeStr));
                } catch(IllegalArgumentException ex) {
                    continue;
                }
            }
        }
        return locales;
    }

    /**
     * Returns all the file names of the resources bundles.
     * 
     * @return the list of file names or {@code null} if the resources are missing.
     */
    private List<String> getAllFileNames() {
        Set<Resource> resources = getAllResources();
        if(resources == null) {
            LOGGER.debug("Missing resources bundles.");
            return null;
        }
        List<String> filenames = new ArrayList<String>(resources.size());
        for(Resource resource : resources) {
            filenames.add(resource.getFilename());
        }
        return filenames;
    }

    /**
     * Gets the array of the prefixes for messages files.
     * 
     * <pre>
     * "WEB-INF/messages"               --> "messages"
     * "classpath:config/i18n/messages" --> "messages"
     * "messages"                       --> "messages"
     * </pre>
     * 
     * @return the array of the prefixes or null if an error occurs.
     */
    private List<String> getMessageFilePrefixes() {
        String[] basenames = getBasenames();
        if(basenames == null) {
            LOGGER.debug("Missing basenames of the resources bundles.");
            return null;
        }
        List<String> prefixes = new ArrayList<String>(basenames.length);
        for(int i = 0; i < basenames.length; ++i) {
            prefixes.add(FilenameUtils.getName(basenames[i]));
        }
        return prefixes;
    }

    /**
     * Returns all the resources bundles.
     * 
     * @return the set of resources or null if {@code basenames} or the {@link ResourceLoader} is missing.
     */
    private Set<Resource> getAllResources() {
        if(cacheResources != null) {
            return cacheResources;
        }
        String[] basenames = getBasenames();
        if(basenames == null) {
            LOGGER.debug("Missing basenames of the resources bundles.");
            return null;
        }
        ResourceLoader resourceLoader = getResourceLoader();
        if(resourceLoader == null) {
            LOGGER.debug("Missing ResourceLoader.");
            return null;
        }

        Set<Resource> resources = new HashSet<Resource>();
        for(String basename : basenames) {
            for(Locale locale : Locale.getAvailableLocales()) {
                List<String> filenames = calculateFilenamesForLocale(basename, locale);
                for(String filename : filenames) {
                    Resource resource = resourceLoader.getResource(filename + PROPERTIES_SUFFIX);
                    if( ! resource.exists()) {
                        resource = resourceLoader.getResource(filename + XML_SUFFIX);
                    }
                    if(resource.exists()) {
                        resources.add(resource);
                    }
                }
            }
        }
        cacheResources = resources;
        return resources;
    }

    /**
     * Gets the array of basenames, each following the basic ResourceBundle convention of not specifying file extension or language codes.
     * 
     * @return the array of basenames or null if an error occurs.
     * 
     * @see org.springframework.context.support.ReloadableResourceBundleMessageSource#setBasenames
     */
    private String[] getBasenames() {
        Field field = ReflectionUtils.findField(org.springframework.context.support.ReloadableResourceBundleMessageSource.class, "basenames");
        if(field == null) {
            LOGGER.debug("Missing field 'basenames' from 'org.springframework.context.support.ReloadableResourceBundleMessageSource' class.");
            return null;
        }
        ReflectionUtils.makeAccessible(field);
        try {
            return (String[]) field.get(this);
        } catch(Exception ex) {
            LOGGER.debug("Unable to get the 'basenames' field value from the 'org.springframework.context.support.ReloadableResourceBundleMessageSource' class.");
            return null;
        }
    }

    /**
     * Gets the resource loader.
     * 
     * @return the resource loader.
     * 
     * @see org.springframework.context.support.ReloadableResourceBundleMessageSource#setResourceLoader
     */
    private ResourceLoader getResourceLoader() {
        Field field = ReflectionUtils.findField(org.springframework.context.support.ReloadableResourceBundleMessageSource.class, "resourceLoader");
        if(field == null) {
            LOGGER.debug("Missing field 'resourceLoader' from 'org.springframework.context.support.ReloadableResourceBundleMessageSource' class.");
            return null;
        }
        ReflectionUtils.makeAccessible(field);
        try {
            return (ResourceLoader) field.get(this);
        } catch(Exception ex) {
            LOGGER.debug("Unable to get the 'resourceLoader' field value from the 'org.springframework.context.support.ReloadableResourceBundleMessageSource' class.");
            return null;
        }
    }
}

如果你想使用这两个功能（获取可用的 Locales 并从属性文件中获取所有 Spring 消息），那么你需要获取这个完整的类。

使用这个ReloadableResourceBundleMessageSource非常简单。
您需要声明资源包：

<!-- Custom message source. -->
<bean id="messageSource" class="fr.ina.archibald.web.support.ReloadableResourceBundleMessageSource">
    <property name="basename" value="classpath:config/i18n/messages" />
    <property name="defaultEncoding" value="UTF-8" />
</bean>

然后，您只需将资源包注入到您想要获取可用Locale的类中：

@Inject
private ReloadableResourceBundleMessageSource resourceBundleMessageSource;

这里是一个使用示例，用于在自动更新浏览器的浏览Locale之前检查Locale是否可用当 Spring LocaleChangeInterceptor 检测到更改时数据库上的用户（例如通过 URL => 'http://your.domain? lang=en'):

package fr.ina.archibald.web.resolver;

import java.util.Locale;

import javax.inject.Inject;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.slf4j.Logger;

import fr.ina.archibald.commons.annotation.Log;
import fr.ina.archibald.dao.entity.UserEntity;
import fr.ina.archibald.security.entity.CustomUserDetails;
import fr.ina.archibald.security.util.SecurityUtils;
import fr.ina.archibald.service.UserService;
import fr.ina.archibald.web.support.ReloadableResourceBundleMessageSource;

/**
 * Custom SessionLocaleResolver.
 * 
 * @author srambeau
 * 
 * @see org.springframework.web.servlet.i18n.SessionLocaleResolver
 */
public class SessionLocaleResolver extends org.springframework.web.servlet.i18n.SessionLocaleResolver {

    @Log
    private Logger logger;

    @Inject
    private UserService userService;

    @Inject
    private ReloadableResourceBundleMessageSource resourceBundleMessageSource;

    @Override
    public void setLocale(HttpServletRequest req, HttpServletResponse res, Locale newLocale) {
        super.setLocale(req, res, newLocale);
        updateUserLocale(newLocale);
    }

    // /**
    // * Returns the default Locale that this resolver is supposed to fall back to, if any.
    // */
    // @Override
    // public Locale getDefaultLocale() {
    // return super.getDefaultLocale();
    // }

    // ********************** PRIVATE METHODES **********************

    /**
     * Updates the locale of the currently logged in user with the new Locale.
     * <p>
     * The locale is not updated if the specified locale is {@code null} or the same as the previous, if the user is missing or if an error occurs.
     * </p>
     * 
     * @param newLocale the new locale.
     */
    private void updateUserLocale(final Locale newLocale) {
        if(newLocale == null) {
            logger.debug("Cannot update the user's browsing locale. The new locale is null.");
            return;
        }
        CustomUserDetails userDetails = SecurityUtils.getCurrentUser();
        if(userDetails == null || userDetails.getUser() == null) {
            logger.debug("Cannot update the user's browsing locale. The user is missing.");
            return;
        }
        UserEntity user = userDetails.getUser();
        // Updates the user locale if and only if the locale has changed and is available on the application.
        if(newLocale.equals(user.getBrowsingLocale()) || ! resourceBundleMessageSource.isAvailableLocale(newLocale)) {
            return;
        }
        user.setBrowsingLocale(newLocale);
        try {
            userService.update(user);
        } catch(Exception ex) {
            logger.error("The browsing locale of the user with identifier " + user.getUserId() + " cannot be updated.", ex);
        }
    }

}

相应的 SessionLocaleResolver 声明：

<!-- This custom SessionLocaleResolver allows to update the user Locale when it change. -->
<bean id="localeResolver" class="fr.ina.archibald.web.resolver.SessionLocaleResolver">
    <property name="defaultLocale" value="fr" />
</bean>

我希望这对您有用...

享受吧！ :-)

Answer 6

如果有人仍在寻找简洁的答案，希望这会有所帮助：

import org.springframework.core.io.Resource;

@Configuration
class LanguageConfig {

    private final Set<Locale> availableLocals;

    public LanguageConfig(@Value("classpath:messages_*.properties") final Resource[] localesResources) {
        availableLocals = getAvailableLocalesFromResources(localesResources);
    }

    private Set<Locale> getAvailableLocalesFromResources(Resource[] localesResources) {
        return Arrays.stream(localesResources).map(resource -> {
            final String localeCode = resource.getFilename().split("messages_")[1].split(".properties")[0];
            return Locale.forLanguageTag(localeCode);
        }).collect(Collectors.toSet());
    }
}

想法是Autowire所有可用的消息源messages_*.properties并根据文件名派生可用的区域设置。
默认区域设置可以单独标记为受支持，如下所示：

availableLocals.add(Locale.getDefault()); // for default messages.properties