解决 Spring Boot enable like in web.xml 报错问题

今天，临近下班时间，我刚准备走呢？群里一位网友一直夸我，夸的我心虚。夸着夸着突然给我来一个问题，问我 Spring Boot enable <async-supported> like in web.xml 怎么解决。Spring Boot 中根本就没有 xml 配置文件的地方，你说这个问题我需要怎么解决呢？

答案就是看本文内容。贴给我的错误内容如下：

Async support must be enabled on a servlet and for all filters involved in async request processing. This is done in Java code using the Servlet API or by adding /"<async-supported>true</async-supported>/" to servlet and filter declarations in web.xml.

stackoverflow 上有一个更具体的错误。异常信息如下：

java.lang.IllegalArgumentException: Async support must be enabled on a servlet and for all filters involved in async request processing. This is done in Java code using the Servlet API or by adding "<async-supported>true</async-supported>" to servlet and filter declarations in web.xml. Also you must use a Servlet 3.0+ container
    at org.springframework.util.Assert.isTrue(Assert.java:65)
    at org.springframework.http.server.ServletServerHttpAsyncRequestControl.<init>(ServletServerHttpAsyncRequestControl.java:59)
    at org.springframework.http.server.ServletServerHttpRequest.getAsyncRequestControl(ServletServerHttpRequest.java:202)
    at org.springframework.web.socket.sockjs.transport.session.AbstractHttpSockJsSession.handleInitialRequest(AbstractHttpSockJsSession.java:202)
    at org.springframework.web.socket.sockjs.transport.handler.AbstractHttpSendingTransportHandler.handleRequestInternal(AbstractHttpSendingTransportHandler.java:66)
    at org.springframework.web.socket.sockjs.transport.handler.AbstractHttpSendingTransportHandler.handleRequest(AbstractHttpSendingTransportHandler.java:58)
    at org.springframework.web.socket.sockjs.transport.TransportHandlingSockJsService.handleTransportRequest(TransportHandlingSockJsService.java:254)
    at org.springframework.web.socket.sockjs.support.AbstractSockJsService.handleRequest(AbstractSockJsService.java:322)
    at org.springframework.web.socket.sockjs.support.SockJsHttpRequestHandler.handleRequest(SockJsHttpRequestHandler.java:88)
    at org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter.handle(HttpRequestHandlerAdapter.java:51)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:938)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:863)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    ...

解决办法如下：

@Bean
public ServletRegistrationBean dispatcherServlet() {
    ServletRegistrationBean registration = new ServletRegistrationBean(
            new DispatcherServlet(), "/");
    registration.setAsyncSupported(true);
    return registration;
}

我们需要重新定义 dispatcherServlet 的实例。然后重启服务，完美解决！

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