ServletContext context=getServletContext()找不到符号

最后调试结果为ServletContext context=getServletContext()找不到符号
import java.io.IOException;
import java.io.PrintWriter;import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;public class CounterServlet 
{ 
public void doGet(HttpServletRequest req,HttpServletResponse resp)throws ServletException,IOException
{
ServletContext context=getServletContext();
Integer count=null;
synchronized(context)
{
count=(Integer)context.getAttribute("counter");
if(null==count){
count=new Integer(1);

}
else{
count=new Integer(count.intvalue()+1);

}
context.setAttribute("counter",count);
}
resp.setContentType("text/html;charset=gb2312");
PrintWriter out=resp.getWriter();

out.println("<html><head>");
out.println("<title>页面访问统计</title>");
out.println("</head><body>");
out.println("该页面已被访问了"+"<b>"+count+"</b>"+"次");
out.println("</body></html>");
out.close();
} private ServletContext getServletContext() {
// TODO Auto-generated method stub
return null;
}

    
}