父子线程间传值问题以及在子线程或者异步情况下使用RequestContextHolder.getRequestAttributes()的注意事项和解决办法

用到的工具类：

java 复制代码

@Slf4j
@Configuration
@Lazy(false)
public class SpringContextUtil{
  public static HttpServletRequest getRequest() {
    ServletRequestAttributes servletRequestAttributes = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
    if (servletRequestAttributes == null) {
        throw new RuntimeException("无法获取servletRequestAttributes ");
    } else {
        return servletRequestAttributes.getRequest();
    }
 }

}

第一种情况（子线程无法获取到父线程的值）：

java 复制代码

    @GetMapping("/threadValueTransfer1")
    private void ThreadValueTransfer1(){
        log.info("开始主线程:{},打印请求头信息--》{}",Thread.currentThread(),SpringContextUtil.getRequest().getHeader("age"));
        new Thread(()->{
            String age = SpringContextUtil.getRequest().getHeader("age");
            log.info ("开始子线程：{},打印请求头信息--》{}",Thread.currentThread(),age);
        }).start();
    }

结果：

解决办法：

java 复制代码

  @GetMapping("/threadValueTransfer2")
    private void ThreadValueTransfer2() throws InterruptedException {
        log.info("开始主线程:{},打印请求头信息--》{}",Thread.currentThread(),SpringContextUtil.getRequest().getHeader("age"));
        RequestContextHolder.setRequestAttributes(RequestContextHolder.getRequestAttributes(), true);
        new Thread(()->{
            String age = SpringContextUtil.getRequest().getHeader("age");
            log.info ("开始子线程：{},打印请求头信息--》{}",Thread.currentThread(),age);
        }).start();
    }

使用RequestContextHolder.setRequestAttributes(RequestContextHolder.getRequestAttributes(), true);开启父子线程间通信

第二中情况（主线程结束，子线程无法获取到值）：

java 复制代码

  @GetMapping("/threadValueTransfer3")
    private void threadValueTransfer3() throws InterruptedException {
        log.info("开始主线程:{},打印请求头信息--》{}",Thread.currentThread(),SpringContextUtil.getRequest().getHeader("age"));
        RequestContextHolder.setRequestAttributes(RequestContextHolder.getRequestAttributes(), true);
        new Thread(()->{
            try {
                Thread.sleep(3*1000);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
            String age = SpringContextUtil.getRequest().getHeader("age");
            log.info ("开始子线程：{},打印请求头信息--》{}",Thread.currentThread(),age);
        }).start();
    }

结果：

解决（使用阿里的ttl）

步骤：

1.拦截器拦截将请求头中信息放到TransmittableThreadLocal中

2.注册拦截器

3.使用

依赖：

java 复制代码

        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>transmittable-thread-local</artifactId>
            <version>2.6.0</version>
        </dependency>

TransmittableThreadLocal上下文工具类

java 复制代码

public class AgeContext {

    private static final ThreadLocal<String> AGE = new TransmittableThreadLocal<>();

    public static String get() {
        return AGE.get();
    }

    public static void set(String age) {
        AGE.set(age);
    }

    public static void clean() {
        if (AGE.get() != null) {
            AGE.remove();
        }
    }

}

拦截器

java 复制代码

public class RequestInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        String age = request.getHeader("age");
        AgeContext.set(age);
        return true;
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        AgeContext.clean();
    }
}

java 复制代码

@Configuration
public class WebMvcConfig implements WebMvcConfigurer {

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new RequestInterceptor())
                .addPathPatterns("/**")
                .excludePathPatterns("/login", "/register");
    }
}

使用：

java 复制代码

 @GetMapping("/threadValueTransfer4")
    private void threadValueTransfer4() throws InterruptedException {
        log.info("开始主线程:{},打印请求头信息--》{}",Thread.currentThread(),AgeContext.get());
        new Thread(()->{
            try {
                Thread.sleep(3*1000);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
            String age = AgeContext.get();
            log.info ("开始子线程：{},打印请求头信息--》{}",Thread.currentThread(),age);
        }).start();
    }

结果：

注意：

阿里的ttl用法就是ThreadLocal的用法，具体参照：积累知识库：ThreadLocal在工作中是怎么使用_analysiscontext threadlocal-CSDN博客