springMVC源码分析--国际化LocaleResolver（一）

        springMVC给我们提供了国际化支持，简单来说就是设置整个系统的运行语言，然后根据系统的运行语言来展示对应语言的页面，一般我们称之为多语言。springMVC国际化机制就是可以设置整个系统的运行语言，其定义了一个国际化支持接口LocaleResolver，提供的默认实现类如下图。



springMVC国际化提供了四个默认实现的类AcceptHeaderLocaleResolver，FixedLocaleResolver、CookieLocaleResolver和SessionLocaleResolver。接下来我们简单介绍一下这四个实现类的源码。

AcceptHeaderLocaleResolver：其实没有任何具体实现，是通过浏览器头部的语言信息来进行多语言选择。

public class AcceptHeaderLocaleResolver implements LocaleResolver {

@Override
public Locale resolveLocale(HttpServletRequest request) {
return request.getLocale();
}

@Override
public void setLocale(HttpServletRequest request, HttpServletResponse response, Locale locale) {
throw new UnsupportedOperationException(
"Cannot change HTTP accept header - use a different locale resolution strategy");
}

}FixedLocaleResolver：设置固定的语言信息，这样整个系统的语言是一成不变的，用处不大。
public class FixedLocaleResolver extends AbstractLocaleContextResolver {
public FixedLocaleResolver() {
setDefaultLocale(Locale.getDefault());
}
public FixedLocaleResolver(Locale locale) {
setDefaultLocale(locale);
}
public FixedLocaleResolver(Locale locale, TimeZone timeZone) {
setDefaultLocale(locale);
setDefaultTimeZone(timeZone);
}
@Override
public Locale resolveLocale(HttpServletRequest request) {
Locale locale = getDefaultLocale();
if (locale == null) {
locale = Locale.getDefault();
}
return locale;
}
@Override
public LocaleContext resolveLocaleContext(HttpServletRequest request) {
return new TimeZoneAwareLocaleContext() {
@Override
public Locale getLocale() {
return getDefaultLocale();
}
@Override
public TimeZone getTimeZone() {
return getDefaultTimeZone();
}
};
}

@Override
public void setLocaleContext(HttpServletRequest request, HttpServletResponse response, LocaleContext localeContext) {
throw new UnsupportedOperationException("Cannot change fixed locale - use a different locale resolution strategy");
}

}CookieLocaleResolver：将语言信息设置到Cookie中，这样整个系统就可以获得语言信息
public class CookieLocaleResolver extends CookieGenerator implements LocaleContextResolver {

//多语言cookie名称
public static final String LOCALE_REQUEST_ATTRIBUTE_NAME = CookieLocaleResolver.class.getName() + ".LOCALE";

//多语言时区cookie名称
public static final String TIME_ZONE_REQUEST_ATTRIBUTE_NAME = CookieLocaleResolver.class.getName() + ".TIME_ZONE";

//默认的多语言cookie名称
public static final String DEFAULT_COOKIE_NAME = CookieLocaleResolver.class.getName() + ".LOCALE";

private Locale defaultLocale;

private TimeZone defaultTimeZone;

public CookieLocaleResolver() {
setCookieName(DEFAULT_COOKIE_NAME);
}
public void setDefaultLocale(Locale defaultLocale) {
this.defaultLocale = defaultLocale;
}

protected Locale getDefaultLocale() {
return this.defaultLocale;
}

public void setDefaultTimeZone(TimeZone defaultTimeZone) {
this.defaultTimeZone = defaultTimeZone;
}

protected TimeZone getDefaultTimeZone() {
return this.defaultTimeZone;
}

@Override
public Locale resolveLocale(HttpServletRequest request) {
parseLocaleCookieIfNecessary(request);
return (Locale) request.getAttribute(LOCALE_REQUEST_ATTRIBUTE_NAME);
}

@Override
public LocaleContext resolveLocaleContext(final HttpServletRequest request) {
parseLocaleCookieIfNecessary(request);
return new TimeZoneAwareLocaleContext() {
@Override
public Locale getLocale() {
return (Locale) request.getAttribute(LOCALE_REQUEST_ATTRIBUTE_NAME);
}
@Override
public TimeZone getTimeZone() {
return (TimeZone) request.getAttribute(TIME_ZONE_REQUEST_ATTRIBUTE_NAME);
}
};
}
private void parseLocaleCookieIfNecessary(HttpServletRequest request) {
if (request.getAttribute(LOCALE_REQUEST_ATTRIBUTE_NAME) == null) {
// Retrieve and parse cookie value.
Cookie cookie = WebUtils.getCookie(request, getCookieName());
Locale locale = null;
TimeZone timeZone = null;
if (cookie != null) {
String value = cookie.getValue();
String localePart = value;
String timeZonePart = null;
int spaceIndex = localePart.indexOf(' ');
if (spaceIndex != -1) {
localePart = value.substring(0, spaceIndex);
timeZonePart = value.substring(spaceIndex + 1);
}
locale = (!"-".equals(localePart) ? StringUtils.parseLocaleString(localePart) : null);
if (timeZonePart != null) {
timeZone = StringUtils.parseTimeZoneString(timeZonePart);
}
if (logger.isDebugEnabled()) {
logger.debug("Parsed cookie value [" + cookie.getValue() + "] into locale '" + locale +
"'" + (timeZone != null ? " and time zone '" + timeZone.getID() + "'" : ""));
}
}
request.setAttribute(LOCALE_REQUEST_ATTRIBUTE_NAME,
(locale != null ? locale: determineDefaultLocale(request)));
request.setAttribute(TIME_ZONE_REQUEST_ATTRIBUTE_NAME,
(timeZone != null ? timeZone : determineDefaultTimeZone(request)));
}
}

@Override
public void setLocale(HttpServletRequest request, HttpServletResponse response, Locale locale) {
setLocaleContext(request, response, (locale != null ? new SimpleLocaleContext(locale) : null));
}

@Override
public void setLocaleContext(HttpServletRequest request, HttpServletResponse response, LocaleContext localeContext) {
Locale locale = null;
TimeZone timeZone = null;
if (localeContext != null) {
locale = localeContext.getLocale();
if (localeContext instanceof TimeZoneAwareLocaleContext) {
timeZone = ((TimeZoneAwareLocaleContext) localeContext).getTimeZone();
}
addCookie(response, (locale != null ? locale : "-") + (timeZone != null ? ' ' + timeZone.getID() : ""));
}
else {
removeCookie(response);
}
request.setAttribute(LOCALE_REQUEST_ATTRIBUTE_NAME,
(locale != null ? locale: determineDefaultLocale(request)));
request.setAttribute(TIME_ZONE_REQUEST_ATTRIBUTE_NAME,
(timeZone != null ? timeZone : determineDefaultTimeZone(request)));
}

protected Locale determineDefaultLocale(HttpServletRequest request) {
Locale defaultLocale = getDefaultLocale();
if (defaultLocale == null) {
defaultLocale = request.getLocale();
}
return defaultLocale;
}

protected TimeZone determineDefaultTimeZone(HttpServletRequest request) {
return getDefaultTimeZone();
}

}SessionLocaleResolver：与CookieLocaleResolver类似将语言信息放到Session中，这样整个系统就可以从Session中获得语言信息。
public class SessionLocaleResolver extends AbstractLocaleContextResolver {

//语言信息放到session中的名称
public static final String LOCALE_SESSION_ATTRIBUTE_NAME = SessionLocaleResolver.class.getName() + ".LOCALE";

public static final String TIME_ZONE_SESSION_ATTRIBUTE_NAME = SessionLocaleResolver.class.getName() + ".TIME_ZONE";

@Override
public Locale resolveLocale(HttpServletRequest request) {
Locale locale = (Locale) WebUtils.getSessionAttribute(request, LOCALE_SESSION_ATTRIBUTE_NAME);
if (locale == null) {
locale = determineDefaultLocale(request);
}
return locale;
}

@Override
public LocaleContext resolveLocaleContext(final HttpServletRequest request) {
return new TimeZoneAwareLocaleContext() {
@Override
public Locale getLocale() {
Locale locale = (Locale) WebUtils.getSessionAttribute(request, LOCALE_SESSION_ATTRIBUTE_NAME);
if (locale == null) {
locale = determineDefaultLocale(request);
}
return locale;
}
@Override
public TimeZone getTimeZone() {
TimeZone timeZone = (TimeZone) WebUtils.getSessionAttribute(request, TIME_ZONE_SESSION_ATTRIBUTE_NAME);
if (timeZone == null) {
timeZone = determineDefaultTimeZone(request);
}
return timeZone;
}
};
}

@Override
public void setLocaleContext(HttpServletRequest request, HttpServletResponse response, LocaleContext localeContext) {
Locale locale = null;
TimeZone timeZone = null;
if (localeContext != null) {
locale = localeContext.getLocale();
if (localeContext instanceof TimeZoneAwareLocaleContext) {
timeZone = ((TimeZoneAwareLocaleContext) localeContext).getTimeZone();
}
}
WebUtils.setSessionAttribute(request, LOCALE_SESSION_ATTRIBUTE_NAME, locale);
WebUtils.setSessionAttribute(request, TIME_ZONE_SESSION_ATTRIBUTE_NAME, timeZone);
}

protected Locale determineDefaultLocale(HttpServletRequest request) {
Locale defaultLocale = getDefaultLocale();
if (defaultLocale == null) {
defaultLocale = request.getLocale();
}
return defaultLocale;
}

protected TimeZone determineDefaultTimeZone(HttpServletRequest request) {
return getDefaultTimeZone();
}

}

通过源码我们可以了解到springMVC对多语言的支持就是设置Locale的语言信息来实现的，只不过是设置了通过cookie、session等方式设置而已，接下来我们会通过demo来进一步介绍这几种实现方式。