Play framework 国际化

Play的国际化操作还是非常简单的。大概分为四步:

1. 首先在${project_home}/conf/application.conf中定义你要用到的哪些国际化语言

application.langs=en,zh

2. 在${project_home}/conf/下新建两个 message 文件，后缀名跟上面定义的语言一样。

message.en
message.zh

  message.en

welcome = Welcome to China

  message.zh

welcome = 欢迎来到中国

3. 在模板文件里调用这些message

<h1>&{welcome}</h1>

4. 在你的程序启动的时候进行国际化的设置（如果不设置，Play框架会有一套自己的解决方案）

Lang.set("zh")//设置为中文

PS:启动程序之后，你可以在页面上写一个改变国际化语言的按钮，后台处理的时候也是调用这个 Lang.set(locale).

我们来看看Play.Lang类的源代码

package play.i18n;

import java.util.Locale;
import play.Logger;
import play.Play;
import play.mvc.Http;
import play.mvc.Http.Request;
import play.mvc.Http.Response;

/**
 * Language support
 */
public class Lang {

    public static ThreadLocal<String> current = new ThreadLocal<String>();

    /**
     * Retrieve the current language or null
     * @return The current language (fr, ja, it ...) or null
     */
    public static String get() {
        String locale = current.get();
        if (locale == null) {
            // don't have current locale for this request - must try to resolve it
            Http.Request currentRequest = Http.Request.current();
            if (currentRequest!=null) {
                // we have a current request - lets try to resolve language from it
                resolvefrom( currentRequest );
            } else {
                // don't have current request - just use default
                setDefaultLocale();
            }
            // get the picked locale
            locale = current.get();
        }
        return locale;
    }



    /**
     * Force the current language
     * @param locale (fr, ja, it ...)
     * @return false if the language is not supported by the application
     */
    public static boolean set(String locale) {
        if (locale.equals("") || Play.langs.contains(locale)) {
            current.set(locale);
            return true;
        } else {
            Logger.warn("Locale %s is not defined in your application.conf", locale);
            return false;
        }
    }

    /**
     * Clears the current language - This wil trigger resolving language from request
     * if not manually set.
     */
    public static void clear() {
        current.remove();
    }


    /**
     * Change language for next requests 
     * @param locale (fr, ja, it ...)
     */
    public static void change(String locale) {
        if (set(locale)) {
            Response.current().setCookie(Play.configuration.getProperty("application.lang.cookie", "PLAY_LANG"), locale);
        }
    }

    /**
     * Guess the language for current request in the following order:
     * [list=1]
     * [*]if a <b>PLAY_LANG</b> cookie is set, use this value

     * [*]if <b>Accept-Language</b> header is set, use it only if the Play! application allows it.<br/>supported language may be defined in application configuration, eg : [i]play.langs=fr,en,de)[/i]

     * <li>otherwise, server's locale language is assumed
     * [/list]
     * @param request
     */
    private static void resolvefrom(Request request) {
        // Check a cookie
        String cn = Play.configuration.getProperty("application.lang.cookie", "PLAY_LANG");
        if (request.cookies.containsKey(cn)) {
            String localeFromCookie = request.cookies.get(cn).value;
            if (localeFromCookie != null && localeFromCookie.trim().length()>0) {
                if (set(localeFromCookie)) {
                    // we're using locale from cookie
                    return;
                }
                // could not use locale from cookie - clear the locale-cookie
                Response.current().setCookie(cn, "");

            }

        }
        // Try from accept-language - look for an exact match
        for (String a: request.acceptLanguage()) {
            a = a.replace("-", "_").toLowerCase();
            for (String locale: Play.langs) {
                if (locale.toLowerCase().equals(a)) {
                    set(locale);
                    return;
                }
            }
        }
        // now see if we have a country-only match
        for (String a: request.acceptLanguage()) {
            if (a.indexOf("-") > 0) {
                a = a.substring(0, a.indexOf("-"));
            }
            for (String locale: Play.langs) {
                if (locale.equals(a)) {
                    set(locale);
                    return;
                }
            }
        }
        // Use default
        setDefaultLocale();
    }

    public static void setDefaultLocale() {
        if (Play.langs.isEmpty()) {
            set("");
        } else {
            set(Play.langs.get(0));
        }
    }

    /**
     *
     * @return the default locale if the Locale cannot be found otherwise the locale
     * associated to the current Lang.
     */
    public static Locale getLocale() {
        String lang = get();
        Locale locale = getLocale(lang);
        if (locale != null) {
            return locale;
        }
        return Locale.getDefault();
    }

     public static Locale getLocale(String lang) {
        for (Locale locale : Locale.getAvailableLocales()) {
            if (locale.getLanguage().equals(lang)) {
                return locale;
            }
        }
        return null;
    }

}

不难看出，Play在获取国际化设置的时候大概是这么处理的：

1.首先从 ThreadLocal 中获取，这个地方是由开发者在代码手动 set 的，也就是 Lang.set("zh")这样的。

2.如果 ThreadLocal 没有，则框架会自己去尝试解决，首先会从 Cookie 中获取，如果没有就从 HTTP 请求中获取 Header 的 accept-language 。如果还没有，那么就会去做一个默认的设置。默认的设置规则是：如果 application.conf 有定义的话，那么取第一个，如果没有，那么设置为空字符串“”。


以上的整个过程仅是我个人见解，欢迎指正:)

PS:eweb4j也马上要支持国际化啦。