问题：

HTTP Status 500 - Error instantiating servlet class RecommenderServlet

type Exception report

message Error instantiating servlet class RecommenderServlet

description The server encountered an internal error that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: Error instantiating servlet class RecommenderServlet
	org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
	org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
	org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
	org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
	org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
	org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
	org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
	java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	java.lang.Thread.run(Thread.java:745)

root cause

java.lang.ClassNotFoundException: RecommenderServlet
	org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1714)
	org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1559)
	org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
	org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
	org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
	org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
	org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
	org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
	org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
	java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	java.lang.Thread.run(Thread.java:745)

解决方法：问题出在web.xml上，<servlet-class>xxx</servlet-class>应该配置为<servlet-class>servlet所在的包名.servlet的名称</servlet>
　　例如：<servlet-class>cn.fth.servlet.RecommenderServlet</servlet-class>