java.nio.channels.CancelledKeyException

使用nio来进行多线程编程，服务器端缓存了每个客户端连接的 key，当客户端网络断开/离线，非正常退出时，服务器端仍然用缓存的 key 来进行操作，就产生了这个异常。

完整异常信息：

org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet [SpringMVC] in context with path [/smarthome] threw exception [Request processing failed; nested exception is java.nio.channels.CancelledKeyException] with root cause
java.nio.channels.CancelledKeyException
	at sun.nio.ch.SelectionKeyImpl.ensureValid(SelectionKeyImpl.java:73)
	at sun.nio.ch.SelectionKeyImpl.interestOps(SelectionKeyImpl.java:82)
	at com.wanyu.smarthome.gateway.GatewayInstance.sendCommand(GatewayInstance.java:153)
	at com.wanyu.smarthome.mobile.EquipmentMobile.DeferredAdd(EquipmentMobile.java:520)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:215)
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:749)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:690)
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:83)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:945)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:876)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
	at com.wanyu.frame.base.AuthFilter.doFilter(AuthFilter.java:97)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:108)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:94)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
	at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:620)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:509)
	at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1104)
	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:684)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1524)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1480)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Thread.java:745)

异常的捕获：

其实就是一个简单的 try catch 就可以了。

		synchronized (lock) {
			try {
				this.key.interestOps(SelectionKey.OP_READ | SelectionKey.OP_WRITE);
				this.key.selector().wakeup();
			} catch (Exception e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}

解决方法：

通过 try catch 捕获了异常其实也是可以的，但通过一些逻辑判断来避免异常的发生则更优雅的多，效率也会高一些。

if (this.key.isValid()) {
	this.key.interestOps(SelectionKey.OP_READ | SelectionKey.OP_WRITE);
	this.key.selector().wakeup();
} else {
	this.key.cancel();
}

其实像我缓存了每个客户端连接的 key，执行 this.key.cancel(); 是没有什么意义的，应该将其从缓存中删除才对。