jdbctemplate查询为空报错_java空指针异常举例

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问题是在：

Dao类是不能直接new出来的必须是通过 ApplicationContext applicationContext= new

ClassPathXMLApplicationContext(“springmvc.xml”)erDao dao = (UserDao) ac.getBean(“UserDaoId

得到类UserDao的实例化

从而JdbcTemplate 的值才能获得

否则JdbcTemplate的值为null

package springmvc.Servlet;

import java.io.UnsupportedEncodingException;

import javax.servlet.http.HttpServletRequest;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.stereotype.Controller;
import org.springframework.stereotype.Service;
import org.springframework.web.bind.annotation.RequestMapping;

import springmvc.Dao.UserDao;
import springmvc.bean.User;

@Service
@Controller
public class Servlet {

   @RequestMapping(“/insert”)
   public String insert(User user,HttpServletRequest request) {

       ApplicationContext ac=new ClassPathXmlApplicationContext(“springmvc.xml”);
       UserDao dao = (UserDao) ac.getBean(“UserDaoId”);
       try {

           request.setCharacterEncoding(“utf-8”);
           String id = request.getParameter(“userid”);
           String name = request.getParameter(“username”);
           String password = request.getParameter(“userpassword”);
           user = new User(id, name, password);
           System.out.println(user);
            boolean result =dao.insert(user);
            if (result) {

               return “success”;
           }else {

               return “defult” ;
           }

       } catch (UnsupportedEncodingException e) {

           // TODO Auto-generated catch block
           e.printStackTrace();
           return null ;
       }

   }
}