写在后面
在REST接口的实现计划中，后端能够仅仅返回一个code，让前端依据code的内容做自定义的音讯揭示。当然，也有间接显示后端返回音讯的计划。在后端间接返回音讯的计划中，如果要提供多个不同语种国家应用，则须要做国际化音讯的实现。
400 BAD_REQUEST{ "code": "user.email.token", "message": "The email is token."}实现的指标：
- validation的error code能够依照不同语言响应；
- 自定义error code能够依照不同语言响应；
- 指定默认的语言；
版本阐明
spring-boot: 2.1.6.RELEASEsping: 5.1.8.RELEASEjava: openjdk 11.0.13初始化我的项目
<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId></dependency>java增加如下的Controller类和User实体类，其中的ServiceException是一个自定义的异样类，该异样会带上业务处理过程中的异样码。
@Validated@RestController@RequestMapping("/user")public class UserController { private static final String TOKEN_EMAIL = "token@example.com"; @PostMapping public User createUser(@RequestBody @Valid User user) { if (TOKEN_EMAIL.equalsIgnoreCase(user.getEmail())) { String message = String.format("The email %s is token.", user.getEmail()); throw new ServiceException("user.email.token", message); } return user; }}@Datapublic class User { @NotNull @Length(min = 5, max = 12) @Pattern(regexp = "^r.*", message = "{validation.user.username}") private String username; @NotNull @Email private String email; @Range(min = 12, message = "{validation.user.age}") private int age;}Validation中实现国际化信息
根本实现
在默认的SpringBoot配置中，只有在申请中减少Accept-Language的Header即可实现Validation错误信息的国际化。如下的申请会应用返回中文的错误信息。
curl --location --request POST 'http://localhost:8080/user' \--header 'Accept-Language: zh-CN' \--header 'Content-Type: application/json' \--data-raw '{ "username": "xx", "email": "token@example.com", "age": 24}对于自定义的message，如validation.user.username，则只须要在resource目录下创立一个basename为ValidationMessages的国际化信息文件即可实现。
└── resources ├── ValidationMessages.properties ├── ValidationMessages_zh_CN.properties └── application.ymlvalidation.user.age=用户的年龄应该大于{min}.validation.user.username=用户名应该以r字母开始国家化信息文件文件名定义规定：
basename_<language>_<country_or_region>.propertiesValidationMessages_en.propertiesValidationMessages_zh_CN.properties更多的文件，能够到hibernate-validator的github仓库查看（文末会给出链接）。
LocaleResolver解析locale信息
在spring-framework的spring-webmvc/.../i18n中，能够找到如下三种不同的LocaleResolver的实现：
FixedLocaleResolver:- 固定local，不做国际化更改。
- 不可动静更改local，否则抛出
UnsupportedOperationException。
AcceptHeaderLocaleResolver:- 读取request的header中的
Accept-Language来确定local的值。 - 不可动静更改local，否则抛出
UnsupportedOperationException。
- 读取request的header中的
CookieLocaleResolver:- 将local信息保留到cookie中，可配合
LocaleChangeInterceptor应用
- 将local信息保留到cookie中，可配合
SessionLocaleResolver:- 将local信息保留到session中，可配合
LocaleChangeInterceptor应用
- 将local信息保留到session中，可配合
默认应用AcceptHeaderLocaleResolver。
设置指定固定的locale
通过指定spring.mvc.locale-resolver=fixed能够应用固定的locale。如果我的项目只有一种语言能够做该指定，免得客户端没有配置Accept-Language的header而呈现多种不同的语言。
spring: mvc: locale-resolver: fixed locale: en在spring-boot的spring-boot-autoconfig/.../web/serlet中能够找到如下的配置，该配置指定了localeResolver的配置形式。
// spring-boot: spring-boot-autoconfig/.../web/serletpackage org.springframework.boot.autoconfigure.web.servlet;public class WebMvcAutoConfiguration { @Bean @ConditionalOnMissingBean @ConditionalOnProperty(prefix = "spring.mvc", name = "locale") public LocaleResolver localeResolver() { if (this.mvcProperties.getLocaleResolver() == WebMvcProperties.LocaleResolver.FIXED) { return new FixedLocaleResolver(this.mvcProperties.getLocale()); } AcceptHeaderLocaleResolver localeResolver = new AcceptHeaderLocaleResolver(); localeResolver.setDefaultLocale(this.mvcProperties.getLocale()); return localeResolver; }}package org.springframework.boot.autoconfigure.web.servlet;@ConfigurationProperties(prefix = "spring.mvc")public class WebMvcProperties { ... /** * Locale to use. By default, this locale is overridden by the "Accept-Language" * header. */ private Locale locale; /** * Define how the locale should be resolved. */ private LocaleResolver localeResolver = LocaleResolver.ACCEPT_HEADER; ...}通过Url指定Locale
通过LocaleChangeInterceptor获取申请中的lang参数来设定语言，并将locale保留到Cookie中，申请了一次之后，雷同的申请就无需再带上该lang参数，即可应用本来曾经设定的locale。
@Configuration@ConditionalOnProperty(prefix = "spring.mvc", name = "customer-locale-resolver", havingValue = "cookie")public class MvcConfigurer implements WebMvcConfigurer { @Bean public LocaleResolver localeResolver(@Value("${spring.mvc.locale:null}") Locale locale) { CookieLocaleResolver resolver = new CookieLocaleResolver(); if (locale != null) { resolver.setDefaultLocale(locale); } return resolver; } @Bean public LocaleChangeInterceptor localeInterceptor() { LocaleChangeInterceptor localeInterceptor = new LocaleChangeInterceptor(); localeInterceptor.setParamName("lang"); return localeInterceptor; } @Override public void addInterceptors(InterceptorRegistry registry) { registry.addInterceptor(localeInterceptor()); }}curl --location --request POST 'http://localhost:8080/user?lang=en' \--header 'Content-Type: application/json' \--data-raw '{ "username": "rxdxxxx", "email": "token@example.com", "age": 24}'之后的申请只有带上含有设置的cookie即可。
curl --location --request POST 'http://localhost:8080/user' \--header 'Content-Type: application/json' \--header 'Cookie: org.springframework.web.servlet.i18n.CookieLocaleResolver.LOCALE=zh-CN' \--data-raw '{ "username": "rxdxxxx", "email": "token@example.com", "age": 24}'自定义Error Code实现国际化信息
在前文给出的代码中，当email为token@example.com时，抛出邮箱已被占用的异样。自定义异样中的code不是通过validator校验，所以不能通过validator主动解决。须要通过MessageSource来将定义的code转化为message，能够将MessageSource了解为一个key-value构造的类。
在resources目录下创立目录i18n，而后创立以messages为basename的国际化信息文件。如上面的目录构造。
└── resources ├── ValidationMessages.properties ├── ValidationMessages_zh_CN.properties ├── application.yml └── i18n ├── messages.properties ├── messages_en.properties └── messages_zh_CN.propertiesmessage_zh_CN.properties
user.email.token=邮箱已存在在application.yml中增加如下配置，即可让springboot生成含有i18n/messages中的properties的配置了。默认状况下，spring.messages.basename=messages，也就是能够间接在resources目录下创立须要的messages国际化信息文件。这里为了把i18n配置都放到一个目录下才做了批改，也能够不批改。
spring: messages: basename: i18n/messages定义ApiExceptionHandler捕捉指定的异样，并在其中的code转化为message。
package io.github.donespeak.springbootsamples.i18n.support;import io.github.donespeak.springbootsamples.i18n.core.ServiceException;import lombok.extern.slf4j.Slf4j;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.context.MessageSource;import org.springframework.http.HttpHeaders;import org.springframework.http.HttpStatus;import org.springframework.http.ResponseEntity;import org.springframework.web.bind.annotation.ExceptionHandler;import org.springframework.web.bind.annotation.RestControllerAdvice;import org.springframework.web.context.request.WebRequest;import org.springframework.web.servlet.LocaleResolver;import javax.servlet.http.HttpServletRequest;import java.util.Locale;@Slf4j@RestControllerAdvicepublic class ApiExceptionHandler { // 用于获取以后的locale private LocaleResolver localeResolver; // 含有配置的code-message对 private MessageSource messageSource; public ApiExceptionHandler(LocaleResolver localeResolver, MessageSource messageSource) { this.localeResolver = localeResolver; this.messageSource = messageSource; } @ExceptionHandler(ServiceException.class) public ResponseEntity<Object> handleServiceException(ServiceException ex, HttpServletRequest request, WebRequest webRequest) { HttpHeaders headers = new HttpHeaders(); HttpStatus status = HttpStatus.BAD_REQUEST; // 获取以后申请的locale Locale locale = localeResolver.resolveLocale(request); log.info("the local for request is {} and the default is {}", locale, Locale.getDefault()); // 将code转化为message String message = messageSource.getMessage(ex.getCode(), null, locale); ApiError apiError = new ApiError(ex.getCode(), message); log.info("The result error of request {} is {}", request.getServletPath(), ex.getMessage(), ex); return new ResponseEntity(apiError, headers, status); }}code转化为国际化信息的message也就配置实现了。如果对于其余的在ResponseEntityExceptionHandler中定义的Exception也须要做国际化信息转化的话，也能够依照下面解决ServiceException的办法进行定义即可。
源码探索
依照下面的代码操作，曾经能够解决须要实现的性能了。这部分将会解说国际化信息的性能波及到的源码局部。
Springboot如何获取messages文件生成MessageSource
在Springboot的spring-boot-autoconfig中配置MessageSource的Properties类为MessageSourceProperties，该类默认指定了basename为messages。
package org.springframework.boot.autoconfigure.context;public class MessageSourceProperties { ... // 默认值 private String basename = "messages"; ...}上面的MessageSourceAutoConfiguration为配置MessageSource的实现。
package org.springframework.boot.autoconfigure.context;public class MessageSourceAutoConfiguration { ... @Bean public MessageSource messageSource(MessageSourceProperties properties) { ResourceBundleMessageSource messageSource = new ResourceBundleMessageSource(); if (StringUtils.hasText(properties.getBasename())) { // 设置 MessageSource的basename 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; } ...}Validation如何应用到ValidationMessages
springboot的spring-boot-autoconfigure/.../validation/ValidationAutoConfiguration为Validator的配置类。
package org.springframework.boot.autoconfigure.validation;/** * @since 1.5.0 */@Configuration@ConditionalOnClass(ExecutableValidator.class)@ConditionalOnResource(resources = "classpath:META-INF/services/javax.validation.spi.ValidationProvider")@Import(PrimaryDefaultValidatorPostProcessor.class)public class ValidationAutoConfiguration { // 创立Validator @Bean @Role(BeanDefinition.ROLE_INFRASTRUCTURE) @ConditionalOnMissingBean(Validator.class) public static LocalValidatorFactoryBean defaultValidator() { LocalValidatorFactoryBean factoryBean = new LocalValidatorFactoryBean(); // 提供message和LocaleResolver MessageInterpolatorFactory interpolatorFactory = new MessageInterpolatorFactory(); factoryBean.setMessageInterpolator(interpolatorFactory.getObject()); return factoryBean; } @Bean @ConditionalOnMissingBean public static MethodValidationPostProcessor methodValidationPostProcessor(Environment environment, @Lazy Validator validator) { MethodValidationPostProcessor processor = new MethodValidationPostProcessor(); // proxy-target-class="true" 则应用cglib2 boolean proxyTargetClass = environment.getProperty("spring.aop.proxy-target-class", Boolean.class, true); processor.setProxyTargetClass(proxyTargetClass); processor.setValidator(validator); return processor; }}这里重点关注一下MessageInterpolatorFactory类，该类最初会创立一个org.hibernate.validator.messageinterpolatio.ResourceBundleMessageInterpolator。
package org.springframework.boot.validation;public class MessageInterpolatorFactory implements ObjectFactory<MessageInterpolator> { private static final Set<String> FALLBACKS; static { Set<String> fallbacks = new LinkedHashSet<>(); fallbacks.add("org.hibernate.validator.messageinterpolation" + ".ParameterMessageInterpolator"); FALLBACKS = Collections.unmodifiableSet(fallbacks); } @Override public MessageInterpolator getObject() throws BeansException { try { // 这里提供默认的MessageInterpolator，获取到ConfigurationImpl // 最终失去 org.hibernate.validator.messageinterpolation.ResourceBundleMessageInterpolator return Validation.byDefaultProvider().configure().getDefaultMessageInterpolator(); } catch (ValidationException ex) { MessageInterpolator fallback = getFallback(); if (fallback != null) { return fallback; } throw ex; } } ...}ResourceBundleMessageInterpolator是AbstractMessageInterpolator的一个子类，该类定义了validation messages文件的门路，其中org.hibernate.validator.ValidationMessages为hibernate提供的，而用户自定义的为ValidationMessages。
package org.hibernate.validator.messageinterpolation;public abstract class AbstractMessageInterpolator implements MessageInterpolator { /** * The name of the default message bundle. */ public static final String DEFAULT_VALIDATION_MESSAGES = "org.hibernate.validator.ValidationMessages"; /** * The name of the user-provided message bundle as defined in the specification. */ public static final String USER_VALIDATION_MESSAGES = "ValidationMessages"; /** * Default name of the message bundle defined by a constraint definition contributor. * * @since 5.2 */ public static final String CONTRIBUTOR_VALIDATION_MESSAGES = "ContributorValidationMessages"; ...}在Springboot 2.6.0及之后，对validation进行了批改。如果须要应用，则须要依照如下的形式引入：
<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> <version>2.6.2</version></dependency><dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-validation</artifactId> <version>2.6.2</version></dependency>此外，还对MessageInterpolatorFactory进行了批改，容许设置内部的MessageSource。还减少了一个MessageSourceMessageInterpolator来整合messageSource和MessageInterpolator。
public class MessageInterpolatorFactory implements ObjectFactory<MessageInterpolator> { ... private final MessageSource messageSource; public MessageInterpolatorFactory() { this(null); } /** * Creates a new {@link MessageInterpolatorFactory} that will produce a * {@link MessageInterpolator} that uses the given {@code messageSource} to resolve * any message parameters before final interpolation. * @param messageSource message source to be used by the interpolator * @since 2.6.0 */ public MessageInterpolatorFactory(MessageSource messageSource) { // 容许应用内部的messageSource this.messageSource = messageSource; } @Override public MessageInterpolator getObject() throws BeansException { MessageInterpolator messageInterpolator = getMessageInterpolator(); if (this.messageSource != null) { return new MessageSourceMessageInterpolator(this.messageSource, messageInterpolator); } return messageInterpolator; } private MessageInterpolator getMessageInterpolator() { try { return Validation.byDefaultProvider().configure().getDefaultMessageInterpolator(); } catch (ValidationException ex) { MessageInterpolator fallback = getFallback(); if (fallback != null) { return fallback; } throw ex; } } ...}MessageSourceMessageInterpolator会优先应用messageSource解决，再通过messageInterpolator解决。
package org.springframework.boot.validation;class MessageSourceMessageInterpolator implements MessageInterpolator { ... @Override public String interpolate(String messageTemplate, Context context) { return interpolate(messageTemplate, context, LocaleContextHolder.getLocale()); } @Override public String interpolate(String messageTemplate, Context context, Locale locale) { // 优先通过messageSource替换占位符，在通过messageInterpolator做解决 String message = replaceParameters(messageTemplate, locale); return this.messageInterpolator.interpolate(message, context, locale); } ...}如需理解更多的信息，能够去查看org.springframework.validation.beanvalidation。LocalValidatorFactoryBean的源码。
参考
- 本文我的项目源码
- source code of Spring Boot’s Auto-configuration class for MessageSource - Github
- Spring Boot internationalization: Step-by-step - Lokalise Blog
- ValidationMessages files in hibernate-validator repository
- Internationalization - springboot docs