初学监听器，报错找不到，请指正，谢谢。环境为eclipse
报错信息：
严重: Error configuring application listener of class com.imooc.listener.FirstListener
java.lang.ClassNotFoundException: com.imooc.listener.FirstListener
代码：
web.xml为：
<listener>
<listener-class>com.imooc.listener.FirstListener</listener-class>
</listener>
FirstListener监听器类的代码为：
package com.imooc.listener;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
public class FirstListener implements ServletContextListener {
public FirstListener() {
}
@Override
public void contextInitialized(ServletContextEvent sce) {
System.out.println("contextInitialized");
}
@Override
public void contextDestroyed(ServletContextEvent sce) {
System.out.println("contextDestroyed");
}
}
