SpringBoot系列之服务端解析客户端国际化请求

前后端分离的国际化方案，如果每个接口都增加参数，代码量和测试量会很大，最好把语言变量加到请求头并通过拦截器解析。

具体过程如下：

1. 客户端增加请求头 Accept-Language；
2. 服务端增加拦截器，解析请求头Accept-Language中的语言值，并通过LanguageUtil设置到当前线程的语言环境中；
3. 服务端需要返回多语言结果的地方，通过LanguageUtil获取当前请求客户端的语言。

除了请求头，也可以通过cookie实现，但是有些客户端不支持cookie，而且cookie存在被篡改的危险，因此更建议使用标准的请求头。

实现代码

通过 SpringMVC 的 RequestContextUtils 和 java.util.Local ，可以很轻松地解析请求头中的语言标识。

SpringMVC提供了多种国际化的实现方式。

下面一步步讲解代码实现。

pom.xml

使用SpringBoot搭建项目，并且引入Lombok用于简化JavaBean。

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.1.3.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>net.ijiangtao.tech.framework.spring.ispringboot.demo</groupId>
	<artifactId>demo-i18n</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>demo-i18n</name>
	<description>Demo  Spring Boot  project for i18n</description>

	<properties>
		<java.version>1.8</java.version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>

		<dependency>
			<groupId>org.projectlombok</groupId>
			<artifactId>lombok</artifactId>
			<optional>true</optional>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

</project>

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application.properties

配置当前服务的端口。

server.port=8303
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LanguageUtil.java

使用ThreadLocal保存当前线程的环境语言。

/**
 * @author ijiangtao.net
 */
public class LanguageUtil {

    public static final String ZH_CN = "zh_CN";

    public static final String EN_US = "en_US";

    public static final String DEFAULT_LANGUAGE = ZH_CN;

    private String lang;

    private static final ThreadLocal<LanguageUtil> context = new ThreadLocal<LanguageUtil>() {
        @Override
        protected LanguageUtil initialValue() {
            return new LanguageUtil();
        }
    };

    public LanguageUtil() {
        lang = DEFAULT_LANGUAGE;
    }

    public static LanguageUtil getCurrentContext() {
        return (LanguageUtil) context.get();
    }

    public static String getCurrentLang() {
        return getCurrentContext().lang;
    }

    public static void setCurrentLang(String lang) {
        getCurrentContext().lang = lang;
    }

    public static void remove() {
        context.remove();
    }
}
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LanguageInterceptor.java

实现 HandlerInterceptor 接口，拦截并解析请求头中的环境语言，并设置到LanguageUtil中。

import lombok.extern.slf4j.Slf4j;
import net.ijiangtao.tech.framework.spring.ispringboot.demo.i18n.util.LanguageUtil;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.LocaleResolver;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.support.RequestContextUtils;

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

@Slf4j
public class LanguageInterceptor implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {
        log.info("preHandle:请求前调用");

        //请求头 当前语言
        // Accept-Language: zh-CN
        // Accept-Language: en-US
        LocaleResolver localeResolver = RequestContextUtils.getLocaleResolver(request);
        Locale local= localeResolver.resolveLocale(request);

        log.info("local={} , localDisplayName={}",local.toString(),local.getDisplayName());

        LanguageUtil.setCurrentLang(local.toString());
        log.info("LanguageUtil.getCurrentLang() = {}",LanguageUtil.getCurrentLang());

        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
                           ModelAndView modelAndView) throws Exception {
        log.info("postHandle:请求后调用");
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
            throws Exception {
        log.info("afterCompletion:请求调用完成后回调方法，即在视图渲染完成后回调");
    }

}

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InterceptorConfig.java

配置拦截器并使之生效。

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport;

@Configuration
public class InterceptorConfig extends WebMvcConfigurationSupport {

    @Override
    public void addInterceptors(InterceptorRegistry registry){
        registry.addInterceptor(new LanguageInterceptor())
                .addPathPatterns("/**")
                .excludePathPatterns("/noi18n")
                .excludePathPatterns("/onelang");
    }

}

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LanguageController.java

从LanguageController中获取当前线程设置的环境语言，测试效果。

import net.ijiangtao.tech.framework.spring.ispringboot.demo.i18n.util.LanguageUtil;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.ResponseBody;

/**
 *
 * @author ijiangtao.net
 */
@Controller
public class LanguageController {

    @GetMapping("/lang/current")
    @ResponseBody
    public String currentLanguage(){
        return LanguageUtil.getCurrentLang();
    }
}

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