国际化配置

在 src/main/resources 下创建一个 i18n 的目录，并在该目录中按照国际化资源文件命名格式分别创建以下三个文件，
login.properties：无语言设置时生效
login_en_US.properties ：英语时生效
login_zh_CN.properties：中文时生效

以上国际化资源文件创建完成后，IDEA 会自动识别它们，并转换成如下的模式：

然后就可以使用Resource Bundle进行可视化配置，如果没有这个插件，下载Resource Bundle插件

打开任意一个国际化资源文件，并切换为 Resource Bundle 模式，然后点击“+”号，创建所需的国际化属性，如下图。

Spring Boot 已经对 ResourceBundleMessageSource 提供了默认的自动配置。

Spring Boot 通过 MessageSourceAutoConfiguration 对 ResourceBundleMessageSource 提供了默认配置，其部分源码如下。

package org.springframework.boot.autoconfigure.context;

import java.time.Duration;

import org.springframework.boot.autoconfigure.AutoConfigureOrder;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.autoconfigure.condition.ConditionMessage;
import org.springframework.boot.autoconfigure.condition.ConditionOutcome;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.autoconfigure.condition.SearchStrategy;
import org.springframework.boot.autoconfigure.condition.SpringBootCondition;
import org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration.ResourceBundleCondition;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.MessageSource;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.support.AbstractApplicationContext;
import org.springframework.context.support.ResourceBundleMessageSource;
import org.springframework.core.Ordered;
import org.springframework.core.io.Resource;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.core.type.AnnotatedTypeMetadata;
import org.springframework.util.ConcurrentReferenceHashMap;
import org.springframework.util.StringUtils;


@Configuration(proxyBeanMethods = false)
@ConditionalOnMissingBean(name = AbstractApplicationContext.MESSAGE_SOURCE_BEAN_NAME, search = SearchStrategy.CURRENT)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Conditional(ResourceBundleCondition.class)
@EnableConfigurationProperties
public class MessageSourceAutoConfiguration {

	private static final Resource[] NO_RESOURCES = {};

	@Bean
	@ConfigurationProperties(prefix = "spring.messages")
	public MessageSourceProperties messageSourceProperties() {
		return new MessageSourceProperties();
	}

	@Bean
	public MessageSource messageSource(MessageSourceProperties properties) {
		ResourceBundleMessageSource messageSource = new ResourceBundleMessageSource();
		if (StringUtils.hasText(properties.getBasename())) {
			messageSource.setBasenames(StringUtils
					.commaDelimitedListToStringArray(StringUtils.trimAllWhitespace(properties.getBasename())));
		}
		if (properties.getEncoding() != null) {
			messageSource.setDefaultEncoding(properties.getEncoding().name());
		}
		messageSource.setFallbackToSystemLocale(properties.isFallbackToSystemLocale());
		Duration cacheDuration = properties.getCacheDuration();
		if (cacheDuration != null) {
			messageSource.setCacheMillis(cacheDuration.toMillis());
		}
		messageSource.setAlwaysUseMessageFormat(properties.isAlwaysUseMessageFormat());
		messageSource.setUseCodeAsDefaultMessage(properties.isUseCodeAsDefaultMessage());
		return messageSource;
	}

	protected static class ResourceBundleCondition extends SpringBootCondition {

		private static ConcurrentReferenceHashMap cache = new ConcurrentReferenceHashMap<>();

		@Override
		public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) {
			String basename = context.getEnvironment().getProperty("spring.messages.basename", "messages");
			ConditionOutcome outcome = cache.get(basename);
			if (outcome == null) {
				outcome = getMatchOutcomeForBasename(context, basename);
				cache.put(basename, outcome);
			}
			return outcome;
		}

		private ConditionOutcome getMatchOutcomeForBasename(ConditionContext context, String basename) {
			ConditionMessage.Builder message = ConditionMessage.forCondition("ResourceBundle");
			for (String name : StringUtils.commaDelimitedListToStringArray(StringUtils.trimAllWhitespace(basename))) {
				for (Resource resource : getResources(context.getClassLoader(), name)) {
					if (resource.exists()) {
						return ConditionOutcome.match(message.found("bundle").items(resource));
					}
				}
			}
			return ConditionOutcome.noMatch(message.didNotFind("bundle with basename " + basename).atAll());
		}

		private Resource[] getResources(ClassLoader classLoader, String name) {
			String target = name.replace('.', '/');
			try {
				return new PathMatchingResourcePatternResolver(classLoader)
						.getResources("classpath*:" + target + ".properties");
			}
			catch (Exception ex) {
				return NO_RESOURCES;
			}
		}

	}

}

从以上源码可知：
Spring Boot 将 MessageSourceProperties 以组件的形式添加到容器中；
MessageSourceProperties 的属性与配置文件中以“spring.messages”开头的配置进行了绑定；
Spring Boot 从容器中获取 MessageSourceProperties 组件，并从中读取国际化资源文件的 basename（文件基本名）、encoding（编码）等信息，将它们封装到 ResourceBundleMessageSource 中；
Spring Boot 将 ResourceBundleMessageSource 以组件的形式添加到容器中，进而实现对国际化资源文件的管理。

查看 MessageSourceProperties 类，其代码如下。

package org.springframework.boot.autoconfigure.context;

import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.time.Duration;
import java.time.temporal.ChronoUnit;

import org.springframework.boot.convert.DurationUnit;


public class MessageSourceProperties {

	
	private String basename = "messages";

	
	private Charset encoding = StandardCharsets.UTF_8;

	
	@DurationUnit(ChronoUnit.SECONDS)
	private Duration cacheDuration;

	
	private boolean fallbackToSystemLocale = true;

	
	private boolean alwaysUseMessageFormat = false;

	
	private boolean useCodeAsDefaultMessage = false;

	public String getBasename() {
		return this.basename;
	}

	public void setBasename(String basename) {
		this.basename = basename;
	}

	public Charset getEncoding() {
		return this.encoding;
	}

	public void setEncoding(Charset encoding) {
		this.encoding = encoding;
	}

	public Duration getCacheDuration() {
		return this.cacheDuration;
	}

	public void setCacheDuration(Duration cacheDuration) {
		this.cacheDuration = cacheDuration;
	}

	public boolean isFallbackToSystemLocale() {
		return this.fallbackToSystemLocale;
	}

	public void setFallbackToSystemLocale(boolean fallbackToSystemLocale) {
		this.fallbackToSystemLocale = fallbackToSystemLocale;
	}

	public boolean isAlwaysUseMessageFormat() {
		return this.alwaysUseMessageFormat;
	}

	public void setAlwaysUseMessageFormat(boolean alwaysUseMessageFormat) {
		this.alwaysUseMessageFormat = alwaysUseMessageFormat;
	}

	public boolean isUseCodeAsDefaultMessage() {
		return this.useCodeAsDefaultMessage;
	}

	public void setUseCodeAsDefaultMessage(boolean useCodeAsDefaultMessage) {
		this.useCodeAsDefaultMessage = useCodeAsDefaultMessage;
	}

}

通过以上代码，我们可以得到以下 3 点信息：
MessageSourceProperties 为 basename、encoding 等属性提供了默认值；
basename 表示国际化资源文件的基本名，其默认取值为“message”，即 Spring Boot 默认会获取类路径下的 message.properties 以及 message_XXX.properties 作为国际化资源文件；
在 application.porperties/yml 等配置文件中，使用配置参数“spring.messages.basename”即可重新指定国际化资源文件的基本名。

通过以上源码分析可知，Spring Boot 已经对国际化资源文件的管理提供了默认自动配置，我们这里只需要在 Spring Boot 全局配置文件中，使用配置参数“spring.messages.basename”指定我们自定义的国际资源文件的基本名即可，代码如下（当指定多个资源文件时，用逗号分隔）。

由于页面使用的是 Tymeleaf 模板引擎，因此我们可以通过表达式 #{…} 获取国际化内容。

但是这里需要注意的是，访问路径中的login.html是否存在，我直接再将其放在了config下的webConfig文件中进行访问，当然也可以随便命名

Spring MVC 进行国际化时有 2 个十分重要的对象：
Locale：区域信息对象
LocaleResolver：区域信息解析器，容器中的组件，负责获取区域信息对象

我们可以通过以上两个对象对区域信息的切换，以达到切换语言的目的。

Spring Boot 在 WebMvcAutoConfiguration 中为区域信息解析器（LocaleResolver）进行了自动配置，源码如下

       @Override
		@Bean
		@ConditionalOnMissingBean(name = DispatcherServlet.LOCALE_RESOLVER_BEAN_NAME)
		public LocaleResolver localeResolver() {
			if (this.webProperties.getLocaleResolver() == WebProperties.LocaleResolver.FIXED) {
				return new FixedLocaleResolver(this.webProperties.getLocale());
			}
			AcceptHeaderLocaleResolver localeResolver = new AcceptHeaderLocaleResolver();
			localeResolver.setDefaultLocale(this.webProperties.getLocale());
			return localeResolver;
		}

从以上源码可知：
该方法默认向容器中添加了一个区域信息解析器（LocaleResolver）组件，它会根据请求头中携带的“Accept-Language”参数，获取相应区域信息（Locale）对象。
该方法上使用了 @ConditionalOnMissingBean 注解，其参数 name 的取值为 localeResolver（与该方法注入到容器中的组件名称一致），该注解的含义为：当容器中不存在名称为 localResolver 组件时，该方法才会生效。换句话说，当我们手动向容器中添加一个名为“localeResolver”的组件时，Spring Boot 自动配置的区域信息解析器会失效，而我们定义的区域信息解析器则会生效

package org.springframework.web.servlet.i18n;

import java.util.ArrayList;
import java.util.Enumeration;
import java.util.List;
import java.util.Locale;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.lang.Nullable;
import org.springframework.util.StringUtils;
import org.springframework.web.servlet.LocaleResolver;


public class AcceptHeaderLocaleResolver implements LocaleResolver {

	private final List supportedLocales = new ArrayList<>(4);

	@Nullable
	private Locale defaultLocale;


	
	public void setSupportedLocales(List locales) {
		this.supportedLocales.clear();
		this.supportedLocales.addAll(locales);
	}

	
	public List getSupportedLocales() {
		return this.supportedLocales;
	}

	
	public void setDefaultLocale(@Nullable Locale defaultLocale) {
		this.defaultLocale = defaultLocale;
	}

	
	@Nullable
	public Locale getDefaultLocale() {
		return this.defaultLocale;
	}


	@Override
	public Locale resolveLocale(HttpServletRequest request) {
		Locale defaultLocale = getDefaultLocale();
		if (defaultLocale != null && request.getHeader("Accept-Language") == null) {
			return defaultLocale;
		}
		Locale requestLocale = request.getLocale();
		List supportedLocales = getSupportedLocales();
		if (supportedLocales.isEmpty() || supportedLocales.contains(requestLocale)) {
			return requestLocale;
		}
		Locale supportedLocale = findSupportedLocale(request, supportedLocales);
		if (supportedLocale != null) {
			return supportedLocale;
		}
		return (defaultLocale != null ? defaultLocale : requestLocale);
	}

	@Nullable
	private Locale findSupportedLocale(HttpServletRequest request, List supportedLocales) {
		Enumeration requestLocales = request.getLocales();
		Locale languageMatch = null;
		while (requestLocales.hasMoreElements()) {
			Locale locale = requestLocales.nextElement();
			if (supportedLocales.contains(locale)) {
				if (languageMatch == null || languageMatch.getLanguage().equals(locale.getLanguage())) {
					// Full match: language + country, possibly narrowed from earlier language-only match
					return locale;
				}
			}
			else if (languageMatch == null) {
				// Let's try to find a language-only match as a fallback
				for (Locale candidate : supportedLocales) {
					if (!StringUtils.hasLength(candidate.getCountry()) &&
							candidate.getLanguage().equals(locale.getLanguage())) {
						languageMatch = candidate;
						break;
					}
				}
			}
		}
		return languageMatch;
	}

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

}

（1）、修改 login.html 切换语言链接，在请求中携带国际化区域信息，代码如下。

（2）、模仿AcceptHeaderLocaleResolve写配置文件，命名为MyLocalResolver，实现接口LocaleResolver并重写LocaleResolver中的方法

package com.ma.ml.config;

import org.springframework.web.servlet.LocaleResolver;
import org.thymeleaf.util.StringUtils;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.util.Locale;

public class MyLocalResolver implements LocaleResolver {

    

    @Override
    public Locale resolveLocale(HttpServletRequest request) {
        String language = request.getParameter("l");   //获得请求路径中的参数
        Locale locale = Locale.getDefault(); //获取默认的请求，如果没有我们自己配置的国际化设置，就使用默认spring默认的
        if(!StringUtils.isEmpty(language)){ //若请求的链接中含有国家化的参数
        //zh_CN
            String [] strings = language.split("_");
            locale = new Locale(strings[0],strings[1]);  //重新修改默认值
        }
        return locale;
    }


    

    @Override
    public void setLocale(HttpServletRequest request, HttpServletResponse response, Locale locale) {

    }
}

（3）、将其像下面一样使用@Bean注册到spring Mvc中