public class I18nInterceptor implements Interceptor {

    private String localeParaName = "_locale";
    private String resName = "_res";
    private boolean isSwitchView = false;

    public I18nInterceptor() {
    }

    public I18nInterceptor(String localeParaName, String resName) {
        if (StrKit.isBlank(localeParaName))
            throw new IllegalArgumentException("localeParaName can not be blank.");
        if (StrKit.isBlank(resName))
            throw new IllegalArgumentException("resName can not be blank.");

        this.localeParaName = localeParaName;
        this.resName = resName;
    }

    public I18nInterceptor(String localeParaName, String resName, boolean isSwitchView) {
        this(localeParaName, resName);
        this.isSwitchView = isSwitchView;
    }

    // ...

    /**
     * Return the baseName, which is used as base name of the i18n resource file.
     */
    protected String getBaseName() {
        return I18n.defaultBaseName;
    }

    /**
     * 1: use the locale from request para if exists. change the locale write to the cookie
     * 2: use the locale from cookie para if exists.
     * 3: use the default locale
     * 4: use setAttr(resName, resObject) pass Res object to the view.
     */
    public void intercept(Invocation inv) {
        Controller c = inv.getController();
        String localeParaName = getLocaleParaName();
        String locale = c.getPara(localeParaName);

        if (StrKit.notBlank(locale)) {    // change locale, write cookie
            c.setCookie(localeParaName, locale, Const.DEFAULT_I18N_MAX_AGE_OF_COOKIE);
        }
        else {                            // get locale from cookie and use the default locale if it is null
            locale = c.getCookie(localeParaName);
            if (StrKit.isBlank(locale))
                locale = I18n.defaultLocale;
        }

        if (isSwitchView) {
            switchView(locale, c);
        }
        else {
            Res res = I18n.use(getBaseName(), locale);
            c.setAttr(getResName(), res);
        }

        inv.invoke();
    }

    /**
     * 在有些 web 系统中，页面需要国际化的文本过多，并且 css 以及 html 也因为际化而大不相同，
     * 对于这种应用场景先直接制做多套同名称的国际化视图，并将这些视图以 locale 为子目录分类存放，
     * 最后使用本拦截器根据 locale 动态切换视图，而不必对视图中的文本逐个进行国际化切换，省时省力。
     */
    public void switchView(String locale, Controller c) {
        Render render = c.getRender();
        if (render != null) {
            String view = render.getView();
            if (view != null) {
                if (view.startsWith("/"))
                    view = "/" + locale + view;
                else
                    view = locale + "/" + view;

                render.setView(view);
            }
        }
    }
}