当方法返回CompletionStage时,我遇到了一个问题,即我的过滤器运行了两次.从RequestMapping(here)上的文档中,它是受支持的返回值.

A CompletionStage (implemented by CompletableFuture for example) which the application uses to produce a return value in a separate thread of its own choosing,as an alternative to returning a Callable.

由于项目非常复杂,并且有很多并发代码,因此我创建了一个新的简单的spring-boot项目.这是(唯一的)控制器：

@Controller
public class BaseController {
    @RequestMapping("/hello")
    @ResponseBody
    public CompletionStageCompletableFuture.supplyAsync(() -> "Hello World");
    }
}

还有一个过滤器：

@WebFilter
@Component
public class GenericLoggingFilter extends GenericFilterBean {
    @Override
    public void doFilter(ServletRequest request,ServletResponse response,FilterChain chain) throws IOException,ServletException {
        HttpServletRequest httpServletRequest = (HttpServletRequest) request;

        System.out.println(httpServletRequest.getMethod() + " " +
                           httpServletRequest.getRequestURI());

        chain.doFilter(request,response);
    }
}

当我打电话curl http：// localhost：8080 / hello时,它会在控制台上打印两次GET / hello.当我更改控制器方法以返回String时：

@RequestMapping("/hello")
@ResponseBody
public String world() {
    return "Hello World";
}

它只打印一次.即使我将其更改为Callable也会出现此行为,Callable没有真正的并发意义(当然,spring本身可能会将此视为异步请求).

因此,如果spring再次运行整个Web堆栈以获得请求上下文,那么即使这样也没有意义,因为以下内容：

@RequestMapping("/hello")
@ResponseBody
public CompletionStageCompletableFuture.supplyAsync(() -> {
        System.out.println(RequestContextHolder.currentRequestAttributes());
        return "Hello World";
    });
}

抛出异常：IllegalStateException：找不到线程绑定请求…

令人惊讶的是,以下工作：

@RequestMapping("/hello")
@ResponseBody
public Callable