import javax.servlet 出错 can't be resolved
我建的动态web项目，为什么导入javax.servlet包出错，说导不进来。
而java.io包可以导进来？

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* Servlet implementation class for Servlet: HelloWorldServlet
*
*/
public class HelloWorldServlet extends javax.servlet.http.HttpServlet {
/* (non-Java-doc)
* @see javax.servlet.http.HttpServlet#HttpServlet()
*/
public HelloWorldServlet() {
super();
}

/* (non-Java-doc)
* @see javax.servlet.http.HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
}

/* (non-Java-doc)
* @see javax.servlet.http.HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
}

[解决办法]
没有 javax 相关包的 lib 引用