tomcat筛选器不支持异步

jhkqcmku  于 2021-10-10  发布在  Java
关注(0)|答案(1)|浏览(305)

比如标题

@WebFilter("/*")
@Component
@Slf4j
public class FilterDemo1 implements Filter {

    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws ServletException, IOException, IOException {
        new Thread(() -> {
            try {
                chain.doFilter(req, resp);
            } catch (Exception e) {
                log.error("a", e);
            }
        }).start();

    }

}

因此,如果tomcat筛选器中有耗时的任务(如rpc或http),它们必须等待并且不能是异步的

java.lang.NullPointerException: null
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.27.jar:9.0.27]```

[error][1]

  [1]: https://i.stack.imgur.com/tFYTH.png
kzipqqlq

kzipqqlq1#

这个 ServletRequest , ServletResponseFilterChain 对象仅在以下线程上有效: doFilter 被称为。如果希望异步使用它们,则需要启用异步处理(参见jakarta ee教程)。 ServletRequest.startAsync()ServletRequestServletResponse 进入异步模式,但 FilterChain 只能在原始螺纹上使用:
这个 service 方法必须与应用于servlet的所有筛选器在同一线程中运行。
(参见servlet规范)
因此,您需要按照以下步骤进行操作:
当一个新请求通过过滤器时,您调用 ServletRequest.startAsync() 并启动新线程或使用任何其他执行器进行异步筛选(例如。 AsyncContext.start(Runnable) ),
异步任务完成后,将结果写入请求属性并调用 AsyncContext.dispatch() :这将从一开始重新启动过滤器链,
什么时候 doFilter 再次调用时,使用请求的属性执行过滤逻辑并调用 FilterChain.doFilter 例如,您可以使用如下内容:

@WebFilter(asyncSupported = true, urlPatterns = {"/*"}, dispatcherTypes = {DispatcherType.ASYNC, DispatcherType.REQUEST})
public class Filter1 implements Filter {

   @Override
   public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
      switch (request.getDispatcherType()) {
         case REQUEST :
            // First pass: start asynchronous processing
            final AsyncContext asyncContext = request.startAsync();
            new Thread(() -> {
               try {
                  Thread.currentThread().sleep(5000);
               } catch (Exception e) {
                  request.setAttribute("filter1Error", e);
               }
               asyncContext.dispatch();
            }).start();
            break;
         case ASYNC :
            // Second pass: throw or forward
            Exception e = (Exception) request.getAttribute("filter1Error");
            if (e instanceof IOException) {
               throw (IOException) e;
            } else if (e instanceof ServletException) {
               throw (ServletException) e;
            } else if (e != null) {
               throw new ServletException(e);
            }
            chain.doFilter(request, response);
            break;
         default :
      }
   }

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