標(biāo)題起得比較詭異，其實并不是坑，而是jetty似乎壓根就沒做對異步request的ServletRequestListener的特殊處理，如果文中有錯誤歡迎提出，可能自己有所疏漏了。

之前遇到了一個bug，在Listener中重寫requestDestroyed清理資源后，這些資源在異步任務(wù)中就不可用了。
這與預(yù)期不符，直覺上request應(yīng)該在任務(wù)完成之后才觸發(fā)requestDestroyed，而不應(yīng)該是開始異步操作返回后就觸發(fā)。
正確的觸發(fā)時機(jī)應(yīng)該是異步任務(wù)完成之后。
后來查閱了下，發(fā)現(xiàn)servlet 3的規(guī)范中只是增加了異步servlet和異步filter的支持，listener如何處理沒有定義，也就是各個容器的實現(xiàn)可能會差異（我們自己使用的是jetty）。
但講道理的話，合理的實現(xiàn)應(yīng)該判斷當(dāng)前request是否處于異步處理中，如果是的話將銷毀的觸發(fā)的時機(jī)放置在AsyncContext完成之后。

自己試了下使用兩個容器：Tomcat 8.5.15和Jetty 9.4.7.v20170914。

測試代碼比較簡單，為了去除其他框架的影響使用純的servlet api。
servlet：

@WebServlet(asyncSupported = true, urlPatterns = { "/test" }) public class TestServlet extends HttpServlet {private static final long serialVersionUID = 7395865716615939512L;private ExecutorService pool = Executors.newCachedThreadPool();@Overridepublic void destroy() {pool.shutdown();}@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {System.out.println(LocalDateTime.now() + " get start " + request);AsyncContext context = request.startAsync();context.addListener(new AsyncListener() {@Overridepublic void onTimeout(AsyncEvent event) throws IOException {System.out.println(LocalDateTime.now() + " async onTimeout " + event.getSuppliedRequest());}@Overridepublic void onStartAsync(AsyncEvent event) throws IOException {System.out.println(LocalDateTime.now() + " async onStartAsync " + event.getSuppliedRequest());}@Overridepublic void onError(AsyncEvent event) throws IOException {System.out.println(LocalDateTime.now() + " async onError " + event.getSuppliedRequest());}@Overridepublic void onComplete(AsyncEvent event) throws IOException {System.out.println(LocalDateTime.now() + " async onComplete " + event.getSuppliedRequest());}}, request, response);pool.execute(() -> {try {Thread.sleep(TimeUnit.SECONDS.toMillis(5));System.out.println(LocalDateTime.now() + " job done");context.complete();} catch (InterruptedException e) {e.printStackTrace();}});System.out.println(LocalDateTime.now() + " get return");}}

listener:

@WebListener public class TestListener implements ServletRequestListener {@Overridepublic void requestDestroyed(ServletRequestEvent event) {System.out.println(LocalDateTime.now() + " TestListener requestDestroyed " + event.getServletRequest());}@Overridepublic void requestInitialized(ServletRequestEvent event) {System.out.println(LocalDateTime.now() + " TestListener requestInitialized " + event.getServletRequest());}}

使用tomcat返回的結(jié)果:

2017-11-19T16:42:04.256 TestListener requestInitialized org.apache.catalina.connector.RequestFacade@7c2df671 2017-11-19T16:42:04.257 get start org.apache.catalina.connector.RequestFacade@7c2df671 2017-11-19T16:42:04.261 get return 2017-11-19T16:42:09.261 job done 2017-11-19T16:42:09.261 async onComplete org.apache.catalina.connector.RequestFacade@7c2df671 2017-11-19T16:42:09.261 TestListener requestDestroyed org.apache.catalina.connector.RequestFacade@7c2df671

使用jetty返回的結(jié)果：

2017-11-19T16:46:35.231 TestListener requestInitialized (GET //localhost:8080/test)@1124787543 org.eclipse.jetty.server.Request@430ae557 2017-11-19T16:46:35.232 get start (GET //localhost:8080/test)@1124787543 org.eclipse.jetty.server.Request@430ae557 2017-11-19T16:46:35.234 get return 2017-11-19T16:46:35.235 TestListener requestDestroyed [GET //localhost:8080/test]@1124787543 org.eclipse.jetty.server.Request@430ae557 2017-11-19T16:46:40.235 job done 2017-11-19T16:46:58.019 async onComplete [GET //localhost:8080/test]@1124787543 org.eclipse.jetty.server.Request@430ae557

jetty果然沒有講道理... ...

先看下講道理的tomcat，果不其然他做了特殊判斷。
在StandardHostValve的invoke方法中：

if (!request.isAsync() && !asyncAtStart) {context.fireRequestDestroyEvent(request.getRequest()); }

并且銷毀的時機(jī)和預(yù)想的一樣是在AsyncContext完成之后：

public void fireOnComplete() {List<AsyncListenerWrapper> listenersCopy = new ArrayList<>();listenersCopy.addAll(listeners);ClassLoader oldCL = context.bind(Globals.IS_SECURITY_ENABLED, null);try {for (AsyncListenerWrapper listener : listenersCopy) {try {listener.fireOnComplete(event);} catch (Throwable t) {ExceptionUtils.handleThrowable(t);log.warn("onComplete() failed for listener of type [" +listener.getClass().getName() + "]", t);}}} finally {context.fireRequestDestroyEvent(request.getRequest());clearServletRequestResponse();context.unbind(Globals.IS_SECURITY_ENABLED, oldCL);}}

而jetty沒有處理，在ContextHandler的doHandle中沒有異步請求的判斷：

finally{// Handle more REALLY SILLY request events!if (new_context){if (!_servletRequestListeners.isEmpty()){final ServletRequestEvent sre = new ServletRequestEvent(_scontext,request);for (int i=_servletRequestListeners.size();i-->0;)_servletRequestListeners.get(i).requestDestroyed(sre);}if (!_servletRequestAttributeListeners.isEmpty()){for (int i=_servletRequestAttributeListeners.size();i-->0;)baseRequest.removeEventListener(_servletRequestAttributeListeners.get(i));}}}

new_content用來在第一次調(diào)用返回true之后是false，和異步處理無關(guān)。

網(wǎng)上查了些也不清楚為什么jetty沒有像tomcat那樣實現(xiàn)這個，還是jetty希望用戶通過AsyncListener來做處理呢。

轉(zhuǎn)載于:https://www.cnblogs.com/fairjm/p/jetty_ServletRequestListener_async.html

總結(jié)

以上是生活随笔為你收集整理的异步请求中jetty处理ServletRequestListener的坑的全部內(nèi)容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網(wǎng)站內(nèi)容還不錯，歡迎將生活随笔推薦給好友。