SpringMVC的ApplicationContext访问导致NullPointerException

Question

每当我试图获取SpringMVC的ApplicationContext时，都会抛出一个NullPointerException。

这是我的用户道：

package com.markor.smarthome.dao;

import com.markor.smarthome.entities.Users;
import com.markor.smarthome.utilites.SpringContextUtil;
import com.markor.smarthome.utilites.StringUtilty;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.jdbc.core.JdbcTemplate;

import java.util.HashMap;
import java.util.Map;

/**
 * Created by litongjie on 2015/5/12.
 */
public class UserDao {

private JdbcTemplate jdbcTemplate = (JdbcTemplate)         SpringContextUtil.getBeans("jdbcTemplate");
private String isExistSql = "SELECT *  FROM users WHERE user_id=?";
private String addUserSql = "INSERT INTO users(`user_id`,`password`,`name`,`email`,`note`)VALUES(?,?,?,?,?)";

public boolean isExist(String userID) {

    Users user = jdbcTemplate.queryForObject(isExistSql, Users.class, userID);
    //如果为空 返回false不存在
    if (StringUtilty.isNullOrEmpty(user.getUser_id())) {
        return false;
    } else return true;
}

public int AddUser(Users user) {
    System.out.println("begen");
    Map<String, Object> map = new HashMap<>();
    map.put("user_id", user.getUser_id());
    map.put("password", user.getPassword());
    map.put("name", user.getName());
    map.put("email", user.getEmail());
    map.put("note", user.getNote());
    int i = jdbcTemplate.update(addUserSql, map);
    return i;
}

public static void main(String[] args) {
    System.out.println("main begin");
    Users users = new Users();
    users.setUser_id("123");
    users.setName("LI");
    users.setNote("444");
    System.out.println("user end"+users);
    UserDao userDao = new UserDao();
    System.out.print(userDao.AddUser(users));
}
}

package com.markor.smarthome.utilites;

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.test.context.testng.AbstractTestNGSpringContextTests;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;

import javax.servlet.ServletContext;

/**
    * 获取Spring上下文及国际化
 *
 * @author bingchuan -->www.vijun.com
 */
public class SpringContextUtil implements ApplicationContextAware {
    private static ApplicationContext application = null;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext)     throws BeansException {
    this.application = applicationContext;
}

public static ApplicationContext getApplicationContext() {
    return application;
}

public static Object getBeans(String beanname) {
    ApplicationContext applicationContext = getApplicationContext();
    return applicationContext.getBean(beanname);
}

线程“main”java.lang.NullPointerException位于com.markor.smarthome.utilites.SpringContextutil.getBeans（SpringContextutil.java:31)位于com.markor.smarthome.dao.userdao.(userdao.java:18)位于com.markor.smarthome.dao.userdao.main（userdao.java:50)位于sun.reflect.nativeMethodAccessorImpl.Invoke0（原生方法）位于

Answer 1

那看起来完全不对。您的spring上下文是从哪里开始的？如果要在main（）方法的某个地方使用它，就必须编写如下内容：

ApplicationContext applicationContext = new ClassPathXmlApplicationContext("/application-context.xml");

（但在这种情况下，您不需要SpringContextUtil，因为您已经有了上下文）。

但是为什么不将UserDao添加到上下文中，让spring将jdbcTemplate bean注入其中呢？

public class UserDao {
@Autowire
private JdbcTemplate jdbcTemplate;
.....

spring上下文：

<bean id="jdbcTemplate" class=.../>
<bean id="userDao" class="com.markor.smarthome.dao.UserDao"/>