ThreadLocal可以隔離線程變量爪喘，在項(xiàng)目中可以應(yīng)用在存儲當(dāng)前線程信息，例如登錄用戶纠拔，租戶等秉剑，但是在需要異步執(zhí)行時，上下文信息需要手動傳遞稠诲，增加與業(yè)務(wù)無關(guān)的代碼侦鹏，jdk雖然提供了InheritableThreadLocal，但是在使用線程池時臀叙，無法用新值覆蓋舊值導(dǎo)數(shù)數(shù)據(jù)不準(zhǔn)確略水。阿里開源了TransmittableThreadLocal用于支持線程池下的異步信息傳遞。
在微服務(wù)的異步調(diào)用時一些公共信息可以使用TransmittableThreadLocal進(jìn)行傳遞劝萤。
首先創(chuàng)建一個context類存儲用戶信息

public class UserContext {
    private static final ThreadLocal<String> ttl = new TransmittableThreadLocal<>();
    public static void setTtl(String s) {
        ttl.set(s);
    }

    public static String getTtl() {
        return ttl.get();
    }

    public static void removeTtl() {
        ttl.remove();
    }
}

配置使用ttl線程池

@Bean(name = "ttlExecutor")
    public Executor ttlExecutor() {
        ThreadPoolTaskExecutor asyncTaskExecutor = new ThreadPoolTaskExecutor();
        asyncTaskExecutor.setMaxPoolSize(2);
        asyncTaskExecutor.setCorePoolSize(2);
        asyncTaskExecutor.setQueueCapacity(10);
        asyncTaskExecutor.setThreadNamePrefix("ttl-async-task-thread-pool-");
        asyncTaskExecutor.initialize();
        asyncTaskExecutor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());
        return TtlExecutors.getTtlExecutor(asyncTaskExecutor);
    }

使用handlerinteceptor攔截請求信息

public class RequestHandlerInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        Enumeration<String> headerNames = request.getHeaderNames();
        HashMap<String, String> requestMap = Maps.newHashMapWithExpectedSize(10);
        while (headerNames.hasMoreElements()) {
            String name = headerNames.nextElement();
            String value = request.getHeader(name);
            requestMap.put(name, value);
        }
        return true;
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable Exception ex) throws Exception {
        //AsyncRequestContextHolder.resetRequestMap();
    }
}

注冊攔截器

public class WebApiAutoConfiguration implements WebMvcConfigurer ｛
 @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(requestHandlerInterceptor).addPathPatterns("/**");
    }
｝

feign調(diào)用時添加header信息到當(dāng)前請求

public class FeignAutoConfiguration {

@Bean
public RequestInterceptor tenantInterceptor() {
    return template -> {
        // 需要清空的信息
        // template.removeHeader("");
         ServletRequestAttributes attributes = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
        if (null == attributes) {
            Map<String, String> requestMap = AsyncRequestContextHolder.getRequestMap();
            requestMap.forEach((name, values) -> {
                // 跳過content-length渊涝，避免Feign報(bào)錯(feign.RetryableException: too many bytes written executing ...)
                if (name.equals("content-length")) {
                    return;
                }
                template.header(name, values);
            }
        }
        else {
            HttpServletRequest request = attributes.getRequest();
            Enumeration<String> headerNames = request.getHeaderNames();

            while (headerNames.hasMoreElements()) {
                String name = headerNames.nextElement();
                String values = request.getHeader(name);

                // 跳過content-length，避免Feign報(bào)錯(feign.RetryableException: too many bytes written executing ...)
                if (name.equals("content-length")) {
                    continue;
                }
               template.header(name, values);
            }
        }
    }
}