HTTP Status 500 - Error instantiating servlet class servlet.ListServlet

type?Exception report

message?Error instantiating servlet class servlet.ListServlet

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

exception

javax.servlet.ServletException: Error instantiating servlet class servlet.ListServlet
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:506)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:962)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:452)
org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1087)
org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:637)
org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
java.lang.Thread.run(Thread.java:662)

root cause

java.lang.ClassNotFoundException: servlet.ListServlet
org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1892)
org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1735)
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:506)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:962)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:452)
org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1087)
org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:637)
org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
java.lang.Thread.run(Thread.java:662)

note?The full stack trace of the root cause is available in the Apache Tomcat/7.0.75 logs.

<?xml?version="1.0"?encoding="UTF-8"?>
<web-app?version="2.5"?
	xmlns="http://java.sun.com/xml/ns/javaee"?
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"?
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee?
	http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
??<display-name></display-name>
??<welcome-file-list>
????<welcome-file>index.jsp</welcome-file>
??</welcome-file-list>
??
??<servlet>
??	<servlet-name>ListServlet</servlet-name>
??	<servlet-class>servlet.ListServlet</servlet-class>
??</servlet>
??<servlet-mapping>
??	<servlet-name>ListServlet</servlet-name>
??	<url-pattern>/List.action</url-pattern>
??</servlet-mapping>
??
??<servlet>
??	<servlet-name>DeleteOneServlet</servlet-name>
??	<servlet-class>servlet.DeleteOneServlet</servlet-class>
??</servlet>
??<servlet-mapping>
??	<servlet-name>DeleteOneServlet</servlet-name>
??	<url-pattern>/DeleteOneServlet.action</url-pattern>
??</servlet-mapping>

</web-app>

<?xml?version="1.0"?encoding="UTF-8"?>
<web-app?version="2.5"?
	xmlns="http://java.sun.com/xml/ns/javaee"?
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"?
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee?
	http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
??<display-name></display-name>
??<welcome-file-list>
????<welcome-file>index.jsp</welcome-file>
??</welcome-file-list>
??
??<servlet>
??	<servlet-name>ListServlet</servlet-name>
??	<servlet-class>servlet.ListServlet</servlet-class>
??</servlet>
??<servlet-mapping>
??	<servlet-name>ListServlet</servlet-name>
??	<url-pattern>/List.action</url-pattern>
??</servlet-mapping>
??
??<servlet>
??	<servlet-name>DeleteOneServlet</servlet-name>
??	<servlet-class>servlet.DeleteOneServlet</servlet-class>
??</servlet>
??<servlet-mapping>
??	<servlet-name>DeleteOneServlet</servlet-name>
??	<url-pattern>/DeleteOneServlet.action</url-pattern>
??</servlet-mapping>

</web-app>

package?Servlet;

import?java.io.IOException;
import?java.io.PrintWriter;
import?java.sql.Connection;
import?java.sql.DriverManager;
import?java.sql.PreparedStatement;
import?java.sql.ResultSet;
import?java.sql.SQLException;
import?java.util.ArrayList;
import?java.util.List;

import?javax.servlet.ServletException;
import?javax.servlet.http.HttpServlet;
import?javax.servlet.http.HttpServletRequest;
import?javax.servlet.http.HttpServletResponse;

import?service.Listservice;
import?service.MaintainService;

import?bean.Message;

@SuppressWarnings({?"serial",?"unused"?})
public?class?ListServlet?extends?HttpServlet?{

	public?ListServlet()?{
		super();
	}

	public?void?destroy()?{
		super.destroy();?//?Just?puts?"destroy"?string?in?log
		//?Put?your?code?here
	}

	
	public?void?doGet(HttpServletRequest?request,?HttpServletResponse?response)
			throws?ServletException,?IOException?{
			?//設置字符編碼
			?request.setCharacterEncoding("utf-8");
			?response.setCharacterEncoding("utf-8");
			?//接受頁面的值
			?String?command=request.getParameter("command");
			?String?description=request.getParameter("description");
			?//向頁面傳值
			?request.setAttribute("command",?command);
			?request.setAttribute("description",?description);
			?Listservice?listservice=new?Listservice();
			?//查詢消息列表并傳給頁面
			?request.setAttribute("messageList",?listservice.queryMessageList(command,?description));
			?//向頁面跳轉
			?request.getRequestDispatcher("/WEB-INF/jsp/back/list.jsp").forward(request,?response);
	}

	public?void?doPost(HttpServletRequest?request,?HttpServletResponse?response)
			throws?ServletException,?IOException?{
		this.doGet(request,?response);
	}

	public?void?init()?throws?ServletException?{
		//?Put?your?code?here
	}

}

我懷疑是xml配置錯了，幫我看看哪不對，謝謝