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Spring WebMVC 国际化处理

读取Locale信息

读取Locale信息的核心接口

org.springframework.web.server.i18n.LocaleContextResolver

该接口用于从Servlet请求中读取Locale信息，核心方法为：org.springframework.web.server.i18n.LocaleContextResolver#resolveLocaleContext

通过查看其对应其实现类，不难看出，Spring WebMVC支持的Locale设置方式一共有以下4种：

  1. org.springframework.web.server.i18n.AcceptHeaderLocaleContextResolver基于header中的Accept-Language选项读取Locale信息，多个传值取第一个。

  2. org.springframework.web.servlet.i18n.CookieLocaleResolver基于Cookie读取Locale设置信息，CookieName默认为CookieLocaleResolver.class.getName() + ".LOCALE"

    从cookie中读取完后，写入到ServletRequest的Attribute属性中，从而贯穿整个请求上下文

  3. org.springframework.web.servlet.i18n.SessionLocaleResolver基于Session设置，实现类似org.springframework.web.servlet.i18n.CookieLocaleResolver

  4. org.springframework.web.servlet.i18n.FixedLocaleResolver全局固定Locale信息，Spring Boot环境中通过配置keyspring.web.locale设置全局Locale环境

Locale信息的存储

org.springframework.context.i18n.LocaleContextHolder

基于ThreadLocal的方式进行存储

private static final ThreadLocal<LocaleContext> localeContextHolder =
			new NamedThreadLocal<>("LocaleContext");
 
	private static final ThreadLocal<LocaleContext> inheritableLocaleContextHolder =
			new NamedInheritableThreadLocal<>("LocaleContext");

同时允许跨线程存储

	public static void setLocale(@Nullable Locale locale, boolean inheritable) {
		LocaleContext localeContext = getLocaleContext();
		TimeZone timeZone = (localeContext instanceof TimeZoneAwareLocaleContext ?
				((TimeZoneAwareLocaleContext) localeContext).getTimeZone() : null);
		if (timeZone != null) {
			localeContext = new SimpleTimeZoneAwareLocaleContext(locale, timeZone);
		}
		else if (locale != null) {
			localeContext = new SimpleLocaleContext(locale);
		}
		else {
			localeContext = null;
		}
		setLocaleContext(localeContext, inheritable);
	}

视图渲染过程中Locale信息的存储

org.springframework.web.servlet.support.RequestContext在创建过程中，再次从HttpServletRequest中读取

		// Determine locale to use for this RequestContext.
		LocaleResolver localeResolver = RequestContextUtils.getLocaleResolver(request);
		if (localeResolver instanceof LocaleContextResolver) {
			LocaleContext localeContext = ((LocaleContextResolver) localeResolver).resolveLocaleContext(request);
			locale = localeContext.getLocale();
			if (localeContext instanceof TimeZoneAwareLocaleContext) {
				timeZone = ((TimeZoneAwareLocaleContext) localeContext).getTimeZone();
			}
		}
		else if (localeResolver != null) {
			// Try LocaleResolver (we're within a DispatcherServlet request).
			locale = localeResolver.resolveLocale(request);
		}

疑惑点：

为什么RequestContext中解析Locale采用的是LocaleResolver#resolveLocaleContext()而在FrameworkServlet中，采用的是ServletRequest#getLocale()

猜测：

RequestContext是和RequestContextUtils是Spring1.0版本即存在的源代码，此时ServletRequest并没有getLocale()方法(Servlet2.3版本引入getLocale()，约2006年左右)。而Spring在后续版本更新中，仍然保留了LocaleResolver的实现。

Spring1.0版本中RequestContextUtils对Locale读取的实现

/**
	 * Retrieves the current locale from the given request,
	 * using the LocaleResolver bound to the request by the DispatcherServlet.
	 * @param request current HTTP request
	 * @return the current locale
	 * @throws IllegalStateException if no LocaleResolver has been found
	 */
	public static Locale getLocale(HttpServletRequest request) throws IllegalStateException {
		return getLocaleResolver(request).resolveLocale(request);
	}

Spring3.0版本中，已经对ServletRequest#getLocale()有所支持

/**
	 * Retrieves the current locale from the given request,
	 * using the LocaleResolver bound to the request by the DispatcherServlet
	 * (if available), falling back to the request's accept-header Locale.
	 * @param request current HTTP request
	 * @return the current locale, either from the LocaleResolver or from
	 * the plain request
	 * @see #getLocaleResolver
	 * @see javax.servlet.http.HttpServletRequest#getLocale()
	 */
	public static Locale getLocale(HttpServletRequest request) {
		LocaleResolver localeResolver = getLocaleResolver(request);
		if (localeResolver != null) {
			return localeResolver.resolveLocale(request);
		}
		else {
			return request.getLocale();
		}
	}

文本国际化处理(JSTL)

在JSTL中，本地化信息Locale的存储则是在javax.servlet.jsp.jstl.fmt.LocalizationContext中。

而LocalizationContext则是存储在ServletRequest的attribute中，贯穿于整个servlet的生命周期。

最终，通过javax.servlet.jsp.jstl.fmt.LocaleSupport#getLocalizedMessage(javax.servlet.jsp.PageContext, java.lang.String, java.lang.Object[], java.lang.String)完成国际化文案的处理

Locale注入时机

org.springframework.web.servlet.DispatcherServlet#render 开始渲染

-> org.springframework.web.servlet.view.AbstractView#renderMergedOutputModel Model属性渲染

—> org.springframework.web.servlet.view.AbstractView#createRequestContext 创建RequestContext，传递Locale信息

---> org.springframework.web.servlet.view.JstlView#exposeHelpers

----> org.springframework.web.servlet.support.JstlUtils#exposeLocalizationContext(javax.servlet.http.HttpServletRequest, org.springframework.context.MessageSource) 根据Request读取Locale，并结合MessageSource，适配LocalizationContext实现,注入到ServletRequest的attribute中

SpringLocalizationContext适配实现

主要实现LocalizationContext#getResourceBundle，利用org.springframework.context.support.MessageSourceResourceBundle完成MessageSource和ResourceBundle之间的适配工作

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