帮忙给解决的菜鸟问题

exception javax.servlet.ServletException: Error instantiating servlet class wm.servlet.sendMess
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:216)
org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:634)
org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:445)
java.lang.Thread.run(Unknown Source)
root cause java.lang.Error: Unresolved compilation problems: 
The import javax.servlet.http cannot be resolved
HttpServlet cannot be resolved to a type
ServletException cannot be resolved to a type
HttpServletRequest cannot be resolved to a type
HttpServletResponse cannot be resolved to a type
ServletException cannot be resolved to a type
RequestDispatcher cannot be resolved to a type
RequestDispatcher cannot be resolved to a type
HttpServletRequest cannot be resolved to a type
HttpServletResponse cannot be resolved to a type
ServletException cannot be resolved to a type wm.servlet.sendMess.<init>(sendMess.java:7)
sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
java.lang.reflect.Constructor.newInstance(Unknown Source)
java.lang.Class.newInstance0(Unknown Source)
java.lang.Class.newInstance(Unknown Source)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:216)
org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:634)
org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:445)
java.lang.Thread.run(Unknown Source)再登陆的时候报上面这个异常，在线等待
sendMess.java
package wm.servlet;import java.util.*;  
import java.sql.*;  
import java.io.*;  
import javax.servlet.*;  
import javax.servlet.http.*;import wm.bean.messFun;public class sendMess extends HttpServlet{


public void init()throws ServletException
    {
    }
public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException{
  messFun MF=new messFun();//创建功能对象
  String username="";
  String title="";
  String keyword="";
  String email="";
  String content="";
  String restore="";
  String msg="";//自定义错误信息
  username=request.getParameter("yhm");
  title=request.getParameter("title");
  keyword=request.getParameter("keyword");
  email=request.getParameter("email");
  content=request.getParameter("content");
  String ip=request.getRemoteHost();
  String sj=MF.gettime();  if(username=="")
  msg+="<li>用户名不能为空</li>";
  else if(!(MF.validLength(username,3,12)))//验证内容的合法性
    msg+="<li>用户名应在3到12位之间</li>";
  if(email=="")
  msg+="<li>邮箱不能为空</li>";
  else if(email.equals("")||(email.indexOf('@')==-1)||(email.indexOf('.')==-1))
    msg+="<li>邮箱格式不正确</li>";
  if(content=="")
msg+="<li>内容不能为空</li>";
  else if(!(MF.validLength(content,10,512)))
    msg+="<li>内容应该在10和100字符之间</li>"; 
  response.setContentType("text/html;charset=GBK"); 
  if(msg.equals(""))//如果没有错误
  {
    boolean result=MF.addMess(ip,title,keyword,email,sj,content,restore,username);
    if(result==true)
    msg+="留言成功";
    else
    msg+="留言失败";
    request.setAttribute("msg",msg);
    RequestDispatcher wm=request.getRequestDispatcher("common.jsp");
    wm.forward(request,response);
    }
else
    {
          request.setAttribute("msg",msg);
  RequestDispatcher wm=request.getRequestDispatcher("common.jsp");
  wm.forward(request,response);
    }
  }
     public void doPost(HttpServletRequest request, HttpServletResponse response) 
        throws ServletException, IOException 
     { 
   doGet(request, response); 
     }  //Clean up resources
    public void destroy()
    {
    }
}
我知道类名该大写，但这个应该不是主要问题
请高手帮忙解决下