springcloud异步上下文

ThreadLocal可以隔离线程变量，在项目中可以应用在存储当前线程信息，例如登录用户，租户等，但是在需要异步执行时，上下文信息需要手动传递，增加与业务无关的代码，jdk虽然提供了InheritableThreadLocal，但是在使用线程池时，无法用新值覆盖旧值导数数据不准确。阿里开源了TransmittableThreadLocal用于支持线程池下的异步信息传递。
在微服务的异步调用时一些公共信息可以使用TransmittableThreadLocal进行传递。
首先创建一个context类存储用户信息

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线程池

@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拦截请求信息

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();
    }
}

注册拦截器

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

feign调用时添加header信息到当前请求

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) -> {
                // 跳过content-length，避免Feign报错(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);

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