最近在进行cometd的移植，之前运行的好好的cometd项目现在总是提示 java.lang.IllegalStateException 错误，仔细来说是 Asynchronous not support！
解决方法： cometd使用了Jetty Continuations来充分利用servlet3.0异步的特性。要求在cometd定义的servlet定义true，还有需要在所有的filter中加true。
示例如下：
<filter>
<filter-name>continuation</filter-name>
<filter-class>org.eclipse.jetty.continuation.ContinuationFilter</filter-class>
<async-supported>true</async-supported>
</filter>
<filter-mapping>
<filter-name>continuation</filter-name>
<url-pattern>/cometd/*</url-pattern>
</filter-mapping>
<servlet>
<servlet-name>cometd</servlet-name>
<servlet-class>org.cometd.annotation.AnnotationCometdServlet</servlet-class>
<init-param>
<param-name>timeout</param-name>
<param-value>30000</param-value>
</init-param>
<init-param>
<param-name>interval</param-name>
<param-value>0</param-value>
</init-param>
<init-param>
<param-name>maxInterval</param-name>
<param-value>10000</param-value>
</init-param>
<init-param>
<param-name>maxLazyTimeout</param-name>
<param-value>5000</param-value>
</init-param>
<init-param>
<param-name>long-polling.multiSessionInterval</param-name>
<param-value>2000</param-value>
</init-param>
<init-param>
<param-name>logLevel</param-name>
<param-value>1</param-value>
</init-param>
<init-param>
<param-name>services</param-name>
<param-value>cn.edu.scut.action.ChatService</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
<async-supported>true</async-supported>
</servlet>
<servlet-mapping>
<servlet-name>cometd</servlet-name>
<url-pattern>/cometd/*</url-pattern>
</servlet-mapping>
具体可参考原文（http://cometd.org/node/106）：
The async-supported element should be specified for the CometD servlet and for all filters that may be executed before the CometD servlet such as the CrossOriginFilter.
