如何在 Spring boot 2 + Webflux + Thymeleaf 中配置 i18n？

Question

我刚开始一个基于 Spring boot 2 + Webflux 的新项目。在升级版本的 spring boot 并将spring-boot-starter-web 替换为spring-boot-starter-webflux 类，如

• WebMvcConfigurerAdapter
• 语言环境解析器
• 语言环境更改拦截器

不见了。现在如何配置 defaultLocale 和拦截器来更改语言？

Answer 1

只需添加一个WebFilter，它会根据查询参数的值设置Accept-Language 标头。以下示例从 http://localhost:8080/examples?language=es 等 URI 上的 language 查询参数获取语言：

import org.springframework.boot.context.event.ApplicationReadyEvent;
import org.springframework.context.ApplicationContext;
import org.springframework.context.event.EventListener;
import org.springframework.http.server.reactive.ServerHttpRequest;
import org.springframework.stereotype.Component;
import org.springframework.util.MultiValueMap;
import org.springframework.web.server.ServerWebExchange;
import org.springframework.web.server.WebFilter;
import org.springframework.web.server.WebFilterChain;
import org.springframework.web.server.adapter.DefaultServerWebExchange;
import org.springframework.web.server.adapter.HttpWebHandlerAdapter;
import reactor.core.publisher.Mono;

import static org.springframework.util.StringUtils.isEmpty;

@Component
public class LanguageQueryParameterWebFilter implements WebFilter {

    private final ApplicationContext applicationContext;

    private HttpWebHandlerAdapter httpWebHandlerAdapter;

    public LanguageQueryParameterWebFilter(final ApplicationContext applicationContext) {
        this.applicationContext = applicationContext;
    }

    @EventListener(ApplicationReadyEvent.class)
    public void loadHttpHandler() {
        this.httpWebHandlerAdapter = applicationContext.getBean(HttpWebHandlerAdapter.class);
    }

    @Override
    public Mono<Void> filter(final ServerWebExchange exchange, final WebFilterChain chain) {
        final ServerHttpRequest request = exchange.getRequest();
        final MultiValueMap<String, String> queryParams = request.getQueryParams();
        final String languageValue = queryParams.getFirst("language");

        final ServerWebExchange localizedExchange = getServerWebExchange(languageValue, exchange);
        return chain.filter(localizedExchange);
    }

    private ServerWebExchange getServerWebExchange(final String languageValue, final ServerWebExchange exchange) {
        return isEmpty(languageValue)
                ? exchange
                : getLocalizedServerWebExchange(languageValue, exchange);
    }

    private ServerWebExchange getLocalizedServerWebExchange(final String languageValue, final ServerWebExchange exchange) {
        final ServerHttpRequest httpRequest = exchange.getRequest()
                .mutate()
                .headers(httpHeaders -> httpHeaders.set("Accept-Language", languageValue))
                .build();

        return new DefaultServerWebExchange(httpRequest, exchange.getResponse(),
                httpWebHandlerAdapter.getSessionManager(), httpWebHandlerAdapter.getCodecConfigurer(),
                httpWebHandlerAdapter.getLocaleContextResolver());
    }
}

它使用@EventListener(ApplicationReadyEvent.class) 以避免循环依赖。

随时对其进行测试并提供有关此 POC 的反馈。

Answer 2

用spring-boot-starter-webflux，有

• 委派WebFlux配置
• Lo​​caleContextResolver

例如，使用查询参数“lang”来显式控制语言环境：

1. 实现LocaleContextResolver，这样 resolveLocaleContext() 返回由“lang”的 GET 参数确定的 SimpleLocaleContext。我将此实现命名为QueryParamLocaleContextResolver。请注意，默认的LocaleContextResolver 是org.springframework.web.server.i18n.AcceptHeaderLocaleContextResolver。

2. 创建一个扩展DelegatingWebFluxConfiguration 的@Configuration 类。覆盖DelegatingWebFluxConfiguration.localeContextResolver() 以返回我们刚刚在步骤1 中创建的QueryParamLocaleContextResolver。将此配置类命名为WebConfig。

3. 在WebConfig 中，覆盖DelegatingWebFluxConfiguration.configureViewResolvers() 并添加ThymeleafReactiveViewResolver bean 作为视图解析器。我们这样做是因为，出于某种原因，DelegatingWebFluxConfiguration 在第 2 步之后会错过ThymeleafReactiveViewResolver。

另外，我必须提到，要将 i18n 与反应式堆栈一起使用，这个 bean 是必要的：

    @Bean
    public MessageSource messageSource() {
        final ReloadableResourceBundleMessageSource messageSource = new ReloadableResourceBundleMessageSource();
        messageSource.setBasenames("classpath:/messages");
        messageSource.setUseCodeAsDefaultMessage(true);
        messageSource.setDefaultEncoding("UTF-8");
        messageSource.setCacheSeconds(5);
        return messageSource;
}

创建一个自然模板、一些属性文件和一个控制器后，您会看到：

• localhost:8080/test?lang=zh给你中文版

• localhost:8080/test?lang=en给你英文版

请不要忘记<head> 中的<meta charset="UTF-8">，否则您可能会看到一些令人讨厌的汉字显示。

Answer 3

另一个使用 spring boot starter web Flux 的解决方案更简洁，是使用 WebHttpHandlerBuilder 定义您自己的 HttpHandler，您可以在其中设置您的 LocaleContextResolver。

文档（参见 1.2.2. WebHandler API）：https://docs.spring.io/spring/docs/current/spring-framework-reference/web-reactive.html#webflux-config-customize

MyLocaleContextResolver.java

public class MyLocaleContextResolver implements LocaleContextResolver {


    @Override
    public LocaleContext resolveLocaleContext(ServerWebExchange exchange) {      
        return new SimpleLocaleContext(Locale.FRENCH);        
    }

    @Override
    public void setLocaleContext(ServerWebExchange exchange, LocaleContext localeContext) {
        throw new UnsupportedOperationException();
    }
}

然后在一个配置文件（注解@Configuration）或你的spring boot应用文件中，定义你自己的HttpHandler bean。

Application.java

@SpringBootApplication
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @Bean
    public HttpHandler httpHandler(ApplicationContext context) {

        MyLocaleContextResolver localeContextResolver = new MyLocaleContextResolver();

        return WebHttpHandlerBuilder.applicationContext(context)
                .localeContextResolver(localeContextResolver) // set your own locale resolver
                .build();

    }

}

就是这样！

Answer 4

从 Spring Boot 2.4.0 开始，WebFluxAutoConfiguration 包含 LocaleContextResolver 的 bean 定义，它允许我们注入自定义 LocaleContextResolver。供参考，以下是 Spring Boot 2.5.4 中默认的 bean 定义（早期版本的实现可能不同）：

@Bean
@Override
@ConditionalOnMissingBean(name = WebHttpHandlerBuilder.LOCALE_CONTEXT_RESOLVER_BEAN_NAME)
public LocaleContextResolver localeContextResolver() {
    if (this.webProperties.getLocaleResolver() == WebProperties.LocaleResolver.FIXED) {
        return new FixedLocaleContextResolver(this.webProperties.getLocale());
    }
    AcceptHeaderLocaleContextResolver localeContextResolver = new AcceptHeaderLocaleContextResolver();
    localeContextResolver.setDefaultLocale(this.webProperties.getLocale());
    return localeContextResolver;
}

您可以提供自己的 LocaleContextResolver 实现，通过提供自定义 bean 定义从查询参数中获取语言环境：

//@Component("localeContextResolver")
@Component(WebHttpHandlerBuilder.LOCALE_CONTEXT_RESOLVER_BEAN_NAME)
public class RequestParamLocaleContextResolver implements LocaleContextResolver {
    @Override
    public LocaleContext resolveLocaleContext(ServerWebExchange exchange) {
        List<String> lang = exchange.getRequest().getQueryParams().get("lang");
        Locale targetLocale = null;
        if (lang != null && !lang.isEmpty()) {
            targetLocale = Locale.forLanguageTag(lang.get(0));
        }
        if (targetLocale == null) {
            targetLocale = Locale.getDefault();
        }
        return new SimpleLocaleContext(targetLocale);
    }

    @Override
    public void setLocaleContext(ServerWebExchange exchange, LocaleContext localeContext) {
        throw new UnsupportedOperationException(
            "Cannot change lang query parameter - use a different locale context resolution strategy");
    }
}

请注意，框架使用具有特定名称 localeContextResolver (WebHttpHandlerBuilder.LOCALE_CONTEXT_RESOLVER_BEAN_NAME) 的 LocaleContextResolver。您需要为 bean 提供给定的名称。见#24209。