java - 从 HttpServletRequest 获取 AsyncContext

Question

我正在使用 Spring 的 OncePerRequestFilter 覆盖 shouldNotFilterAsyncDispatch 方法以返回 false。这样它就可以处理异步请求。在过滤器中，我正在尝试执行以下操作:

if (isAsyncDispatch(request)) {
    request.getAsyncContext().addListener(new AsyncListener() {
        @Override
        public void onComplete(AsyncEvent event) throws IOException {
            System.out.println("onComplete");
        }

        @Override
        public void onTimeout(AsyncEvent event) throws IOException {

        }

        @Override
        public void onError(AsyncEvent event) throws IOException {
            System.out.println("onError");
        }

        @Override
        public void onStartAsync(AsyncEvent event) throws IOException {

        }
    });
}

因此 isAsyncDispatch 按预期返回 true。但是，当我尝试 getAsyncContext 时，它会失败并出现以下异常:

IllegalStateException: It is illegal to call this method if the current request is not in asynchronous mode (i.e. isAsyncStarted() returns false)

确实，request.isAsyncStarted() 返回 false，但是 request.isAsyncSupported() 为 true 而 request.getDispatcherType() 为 异步。

我不明白:它是异步的还是不异步的？也许我以错误的方式使用了 API？如何添加 AsyncListener？可能是因为我使用的是 Tomcat？

提前致谢!

Answer 1

当我过去这样做时，我们已经完成了:

if (request.isAsyncSupported()) {
      AsyncContext asyncContext = request.startAsync();
      // Do whatever with context
}

getAsyncContext() 的 javadoc 声明:(在 ServletRequest 中)

IllegalStateException - if this request has not been put into asynchronous mode, i.e., if neither startAsync() nor startAsync(ServletRequest,ServletResponse) has been called