303 lines
10 KiB
Markdown
303 lines
10 KiB
Markdown
# 精尽 Spring MVC 源码解析 —— LocaleResolver 组件
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> LocaleResolver 实际使用很少，所以艿艿也没特别细看，就看了下 AcceptHeaderLocaleResolver 类。
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>
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> 这里艿艿就转载 N3verL4nd 的 [《SpringMVC 源码解析 —— LocaleResolver》](https://blog.csdn.net/x_iya/article/details/78285318) 。
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# 1. LocaleResolver
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LocaleResolver 是一个解决国际化的策略接口。它包含两个方法：`#resolveLocale(...)` 和 `#setLocale(...)` ，代码如下：
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```
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public interface LocaleResolver {
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Locale resolveLocale(HttpServletRequest request);
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void setLocale(HttpServletRequest request, @Nullable HttpServletResponse response, @Nullable Locale locale);
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}
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```
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实现此接口的类：
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[](http://static.iocoder.cn/47659f045806606287c2d8d3a44f295c)LocaleResolver 类图
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# 2. AcceptHeaderLocaleResolver
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SpringMVC 默认使用的是：AcceptHeaderLocaleResolver 。
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[](http://static.iocoder.cn/41a00a9f69243a72aa4c82f6bb758b05)`DispatcherServlet.properties`
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```
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/**
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* LocaleResolver 接口的实现类
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* 简单地使用 HTTP 请求头里的 Accept-Language 来指定 Locale对象(即客户端浏览器发送的语言环境，通常是客户端的操作系统)
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*
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* 注意:不支持 setLocale 方法，因为只能通过更改客户端的区域设置来更改 Accept-Language 请求头
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*/
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public class AcceptHeaderLocaleResolver implements LocaleResolver {
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private final List<Locale> supportedLocales = new ArrayList<>(4);
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@Nullable
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private Locale defaultLocale;
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/**
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* 配置支持的区域设置列表
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*/
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public void setSupportedLocales(@Nullable List<Locale> locales) {
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this.supportedLocales.clear();
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if (locales != null) {
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this.supportedLocales.addAll(locales);
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}
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}
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/**
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* 返回配置的支持的区域设置列表
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*/
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public List<Locale> getSupportedLocales() {
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return this.supportedLocales;
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}
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/**
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* 如果 HTTP 请求头没有 Accept-Language，则使用该默认的语言环境设置
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*/
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public void setDefaultLocale(@Nullable Locale defaultLocale) {
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this.defaultLocale = defaultLocale;
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}
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/**
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* 返回默认配置的语言环境(如果有)
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*/
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@Nullable
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public Locale getDefaultLocale() {
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return this.defaultLocale;
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}
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@Override
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public Locale resolveLocale(HttpServletRequest request) {
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Locale defaultLocale = getDefaultLocale();
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if (defaultLocale != null && request.getHeader("Accept-Language") == null) {
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return defaultLocale;
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}
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Locale requestLocale = request.getLocale();
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if (isSupportedLocale(requestLocale)) {
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return requestLocale;
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}
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Locale supportedLocale = findSupportedLocale(request);
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if (supportedLocale != null) {
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return supportedLocale;
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}
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return (defaultLocale != null ? defaultLocale : requestLocale);
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}
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private boolean isSupportedLocale(Locale locale) {
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List<Locale> supportedLocales = getSupportedLocales();
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return (supportedLocales.isEmpty() || supportedLocales.contains(locale));
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}
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@Nullable
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private Locale findSupportedLocale(HttpServletRequest request) {
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Enumeration<Locale> requestLocales = request.getLocales();
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while (requestLocales.hasMoreElements()) {
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Locale locale = requestLocales.nextElement();
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if (getSupportedLocales().contains(locale)) {
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return locale;
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}
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}
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return null;
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}
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@Override
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public void setLocale(HttpServletRequest request, @Nullable HttpServletResponse response, @Nullable Locale locale) {
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throw new UnsupportedOperationException(
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"Cannot change HTTP accept header - use a different locale resolution strategy");
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}
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}
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```
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`#resolveLocale(...)` 方法的处理流程：
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- 如果 HTTP 请求头里不含有 `Accept-Language` ，并且默认的语言环境 `defaultLocale` 不为空，则使用默认的语言环境。否则，从请求里获得 Locale 。
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- 而一般的我们没有配置 `supportedLocales` 与`defaultLocale` 属性(需要配置注入)，所以 AcceptHeaderLocaleResolver 使用`Accept-Language` 来构造 Locale 对象。
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# 3. AbstractLocaleResolver
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```
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/**
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* 实现 LocaleResolver 接口的抽象基类
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* 提供对默认语言环境的支持
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*/
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public abstract class AbstractLocaleResolver implements LocaleResolver {
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@Nullable
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private Locale defaultLocale;
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public void setDefaultLocale(@Nullable Locale defaultLocale) {
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this.defaultLocale = defaultLocale;
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}
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@Nullable
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protected Locale getDefaultLocale() {
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return this.defaultLocale;
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}
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}
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```
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# 4. LocaleContextResolver
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```
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public interface LocaleContextResolver extends LocaleResolver {
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LocaleContext resolveLocaleContext(HttpServletRequest request);
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void setLocaleContext(HttpServletRequest request, @Nullable HttpServletResponse response,
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@Nullable LocaleContext localeContext);
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}
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```
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# 5. AbstractLocaleContextResolver
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```
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/**
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* LocaleContextResolver 实现的抽象基类:提供对默认语言环境和默认时区的支持
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* 还提供了 resolveLocale 和 setLocale 的预实现版本，委托给 resolveLocaleContext 和 setLocaleContext
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*/
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public abstract class AbstractLocaleContextResolver extends AbstractLocaleResolver implements LocaleContextResolver {
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@Nullable
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private TimeZone defaultTimeZone;
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public void setDefaultTimeZone(@Nullable TimeZone defaultTimeZone) {
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this.defaultTimeZone = defaultTimeZone;
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}
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@Nullable
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public TimeZone getDefaultTimeZone() {
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return this.defaultTimeZone;
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}
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@Override
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public Locale resolveLocale(HttpServletRequest request) {
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Locale locale = resolveLocaleContext(request).getLocale();
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return (locale != null ? locale : request.getLocale());
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}
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@Override
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public void setLocale(HttpServletRequest request, @Nullable HttpServletResponse response, @Nullable Locale locale) {
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setLocaleContext(request, response, (locale != null ? new SimpleLocaleContext(locale) : null));
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}
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}
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```
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# 6. SessionLocaleResolver
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```
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public class SessionLocaleResolver extends AbstractLocaleContextResolver {
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public static final String LOCALE_SESSION_ATTRIBUTE_NAME = SessionLocaleResolver.class.getName() + ".LOCALE";
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public static final String TIME_ZONE_SESSION_ATTRIBUTE_NAME = SessionLocaleResolver.class.getName() + ".TIME_ZONE";
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private String localeAttributeName = LOCALE_SESSION_ATTRIBUTE_NAME;
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private String timeZoneAttributeName = TIME_ZONE_SESSION_ATTRIBUTE_NAME;
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/**
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* 在 HttpSession 中指定相应属性的名称，保存当前的 Locale 值
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* 默认值为 LOCALE_SESSION_ATTRIBUTE_NAME
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*/
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public void setLocaleAttributeName(String localeAttributeName) {
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this.localeAttributeName = localeAttributeName;
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}
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/**
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* 在 HttpSession 中指定相应属性的名称，保存当前的 TimeZone 值
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* 默认值为 TIME_ZONE_SESSION_ATTRIBUTE_NAME
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*/
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public void setTimeZoneAttributeName(String timeZoneAttributeName) {
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this.timeZoneAttributeName = timeZoneAttributeName;
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}
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@Override
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public Locale resolveLocale(HttpServletRequest request) {
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Locale locale = (Locale) WebUtils.getSessionAttribute(request, this.localeAttributeName);
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if (locale == null) {
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locale = determineDefaultLocale(request);
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}
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return locale;
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}
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@Override
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public LocaleContext resolveLocaleContext(final HttpServletRequest request) {
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return new TimeZoneAwareLocaleContext() {
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@Override
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public Locale getLocale() {
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Locale locale = (Locale) WebUtils.getSessionAttribute(request, localeAttributeName);
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if (locale == null) {
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locale = determineDefaultLocale(request);
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}
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return locale;
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}
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@Override
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@Nullable
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public TimeZone getTimeZone() {
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TimeZone timeZone = (TimeZone) WebUtils.getSessionAttribute(request, timeZoneAttributeName);
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if (timeZone == null) {
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timeZone = determineDefaultTimeZone(request);
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}
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return timeZone;
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}
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};
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}
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@Override
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public void setLocaleContext(HttpServletRequest request, @Nullable HttpServletResponse response,
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@Nullable LocaleContext localeContext) {
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Locale locale = null;
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TimeZone timeZone = null;
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if (localeContext != null) {
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locale = localeContext.getLocale();
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if (localeContext instanceof TimeZoneAwareLocaleContext) {
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timeZone = ((TimeZoneAwareLocaleContext) localeContext).getTimeZone();
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}
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}
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// 将 Locale 与 TimeZone 保存到 HttpSession
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WebUtils.setSessionAttribute(request, this.localeAttributeName, locale);
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WebUtils.setSessionAttribute(request, this.timeZoneAttributeName, timeZone);
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}
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/**
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* 确定给定请求的默认语言环境，如果没有找到 Locale 会话属性，则调用
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* 默认实现返回指定的默认语言环境（如果有的话）返回到请求的Accept-Header 语言环境
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*/
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protected Locale determineDefaultLocale(HttpServletRequest request) {
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Locale defaultLocale = getDefaultLocale();
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if (defaultLocale == null) {
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defaultLocale = request.getLocale();
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}
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return defaultLocale;
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}
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/**
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* 确定给定请求的默认时区，如果未找到TimeZone会话属性，则调用
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* 默认实现返回指定的默认时区（如果有），否则返回null
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*/
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@Nullable
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protected TimeZone determineDefaultTimeZone(HttpServletRequest request) {
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return getDefaultTimeZone();
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}
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}
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```
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# 666. 彩蛋
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参考和推荐如下文章：
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- 韩路彪 [《看透 Spring MVC：源代码分析与实践》](https://item.jd.com/11807414.html) 的 [「第18章 LocaleResolver」](https://svip.iocoder.cn/Spring-MVC/LocaleResolver/#) 小节
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- rj042 [《Spring MVC 之 LocaleResolver(解析用户区域)》](http://blog.csdn.net/rj042/article/details/23354225) |