java - 在 Springboot 应用程序中使用 Rest Template 调用使用 @Async 注解的方法

Question

我在 @Async 和 Rest Template 调用方面遇到问题；这是我的主应用程序类，带有任务执行器 Bean 和 EnableAsync 注释

@SpringBootApplication
@ComponentScan({"org.***"})
@EnableAspectJAutoProxy
@EnableAsync
@EnableAutoConfiguration(exclude={DataSourceAutoConfiguration.class,HibernateJpaAutoConfiguration.class})
@EnableFeignClients(basePackages = {"org.service.feign"})
public class MainApplication extends SpringBootServletInitializer {

    /**
     * <p>main.</p>
     *
     * @param args an array of {@link java.lang.String} objects.
     */
    public static void main(String[] args) {
        SpringApplication.run(MainApplication.class, args);
    }

    @Bean(name = "threadPoolTaskExecutor")
      public Executor taskExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(5);
        executor.setMaxPoolSize(5);
        executor.setQueueCapacity(100);
        executor.setThreadNamePrefix(“CustomLookup-");
        executor.initialize();
        return executor;
      }
    /**
     * Configure.
     *
     * @param application the application
     * @return the spring application builder
     */
    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
        return application.sources(MainApplication.class);
    }
    
    /**
     * <p>requestContextListener.</p>
     *
     * @return a {@link org.springframework.web.context.request.RequestContextListener} object.
     */
    @Bean
    public RequestContextListener requestContextListener() {
        return new RequestContextListener();
   }
}

这是我在 Rest Controller 中调用的带有异步注释的测试服务:

@Service
public class TestService {

   

    @Async("threadPoolTaskExecutor")
    public ResponseEntity<Object> test()
            throws Exception{
        PagedRequest<SearchRequest> request = new PagedRequest<SearchRequest>();

        SearchRequest filters = new Request();

        filters.setCod(“abcdeg");

        request.setFilters(filters);
        RestTemplate restTemplate = new RestTemplate();
        restTemplate.setInterceptors(Collections.singletonList(new RestInterceptor()));  // here I set a custom headers
        final HttpHeaders theJsonHeader = new HttpHeaders();
        theJsonHeader.setContentType(MediaType.APPLICATION_JSON);
        final MultiValueMap<String, Object> theMultipartRequest = new LinkedMultiValueMap<>();
        ObjectMapper objectMapper = new ObjectMapper();
        String someJsonString = objectMapper.writeValueAsString(request);
        theMultipartRequest.add("request", new HttpEntity<>(someJsonString, theJsonHeader));
        ResponseEntity<Object> response = null;
        final HttpEntity<PagedRequest<SearchRequest>> theHttpEntity = new HttpEntity<>(request, theJsonHeader);

        String path = “http://...”; //url removed for privacy

        response = restTemplate.postForEntity(path, theHttpEntity, Object.class);
        return response;
        
    }

}

该服务在其余模板上返回一个空指针；这是堆栈跟踪

java.lang.NullPointerException: null
    at org.springframework.web.client.DefaultResponseErrorHandler.hasError(DefaultResponseErrorHandler.java:61) ~[spring-web-5.2.3.RELEASE.jar:5.2.3.RELEASE]
    at org.springframework.web.client.RestTemplate.handleResponse(RestTemplate.java:773) ~[spring-web-5.2.3.RELEASE.jar:5.2.3.RELEASE]
    at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:743) ~[spring-web-5.2.3.RELEASE.jar:5.2.3.RELEASE]
    at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:677) ~[spring-web-5.2.3.RELEASE.jar:5.2.3.RELEASE]
    at org.springframework.web.client.RestTemplate.postForEntity(RestTemplate.java:452) ~[spring-web-5.2.3.RELEASE.jar:5.2.3.REL

这是我在 RestTemplate 中添加的 RestIntercept 代码

public class RestInterceptor implements ClientHttpRequestInterceptor {

   
    @Override
    public ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution) throws IOException {
        
        ServletRequestAttributes requestAttributes = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
        if (requestAttributes == null)
            return null;
        
        HttpServletRequest req = requestAttributes.getRequest();
        if (req == null || req.getHeader(PrevConstants.USER_KEY)==null || req.getHeader(PrevConstants.JWT_HEADER_NAME)==null)
            return null;


        String userKey = req.getHeader(PrevConstants.USER_KEY);

        String jwt = req.getHeader(PrevConstants.JWT_HEADER_NAME);
        
        if (jwt == null) {
            jwt = "custom jwt";
        }
       
        else if ( !jwt.startsWith("Bearer")) {                     jwt = "Bearer " + jwt;                 }

        request.getHeaders().set(PrevConstants.USER_KEY, userKey);
        request.getHeaders().set(PrevConstants.JWT_HEADER_NAME, jwt);         
        
        ClientHttpResponse response = execution.execute(request, body);
        return response;
    }
}

但如果我删除 @EnableAsync 和 @Async，简单的 Rest 模板就可以完美工作。

当我传递 HttpServlet 请求时，Eclipse 调试显示以下内容:

有什么问题？我不知道。 谢谢您的回复

Answer 1

RequestContextHolder 保存当前线程正在处理的请求的上下文。当您使用 @Async 时，您的拦截器将在与处理请求的线程不同的线程上调用。因此，RequestContextHolder.getRequestAttributes() 返回 null，然后您的拦截器返回 null 响应。为了遵守 ClientHttpRequestInterceptor#intercept 的约定，它必须返回一个非空值，因此这个 null 响应会导致失败。

如果您想使用@Async，则必须在 REST Controller 中检索 RequestAttributes，然后将它们传递到您的 TestService > 作为 test 方法的参数。然后，您可以使用这些属性创建 RestInterceptor，而不是使用 RequestContextHolder 来访问它们:

@Async("threadPoolTaskExecutor")
public ResponseEntity<Object> test(RequestAttributes requestAttributes) throws Exception {
    // …
    RestTemplate restTemplate = new RestTemplate();
    restTemplate.setInterceptors(Collections.singletonList(new RestInterceptor(requestAttributes)));
    // …
}