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。