ServiceImpl调用mapper层代码空指针怎么办？

1. 这是错误信息 

2.这是service代码

package com.blog.service;

import com.blog.mybatis.model.User;
import org.springframework.stereotype.Service;

@Service("UserService")
public interface UserService {
    //登录方法
    public User userLogin(User user);

    //查询账号是否存在
    public int QueryAccount(String account);

    //查询用户
    public User selectUser();
}

3.这是serviceImpl代码

@Service("UserService")
public class UserServiceImpl implements UserService {
    @Autowired(required = false)
    private UserMapper mapper;

    @Override
    public User userLogin(User user) {
        return mapper.userLogin(user);
    }

    @Override
    public int QueryAccount(String account) {
        return mapper.QueryAccount(account);
    }

    @Override
    public User selectUser() {
        return mapper.selectUser();
    }

4.这是mapper代码

public interface UserMapper {
    //登录方法
    public User userLogin(User user);

    //查询账号是否存在
    public int QueryAccount(String account);

    //查询用户
    public User selectUser();
}

5.这是mapper.xml代码

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="service.blog.mybatis.mapper.UserMapper">
    <select id="userLogin" resultType="User">
        select *
        from user
        where acct = #{acct}
          and pwd = #{pwd}
    </select>
    <select id="QueryAccount" resultType="User">
        select email from user where email = #{email}
    </select>
    <select id="selectUser" resultType="User">
        select * from user
    </select>
</mapper>

6.这是controlller代码

@Controller
@RequestMapping("/blog/api")
public class MainController {

    @Autowired(required = false)
    private UserService service;

    private Logger logger = Logger.getLogger(MainController.class);

    @RequestMapping(value = "/check", method = RequestMethod.POST)
    @ResponseBody
    @CrossOrigin
    public Result check() {
        logger.info("MainController run");
        Result result = null;
        User user = service.selectUser();
        //String name = user.getAcct();
        result = new Result();
        result.setMessage("账号");
        return result;
    }

配置文件

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:tx="http://www.springframework.org/schema/tx"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/tx
                           http://www.springframework.org/schema/tx/spring-tx.xsd
                           http://www.springframework.org/schema/beans
                           http://www.springframework.org/schema/beans/spring-beans-4.1.xsd
                            http://www.springframework.org/schema/context
                             http://www.springframework.org/schema/context/spring-context.xsd"
       default-lazy-init="true">


    <context:annotation-config/>
    <!--扫描全包-->
    <context:component-scan base-package="com.blog.*"/>
    <!--加载数据库文件-->
    <context:property-placeholder location="classpath:jdbc.properties"/>

    <!-- 写数据源 -->
    <!--配置dataSource对象，然后通过配置到transactionManager中-->
    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource">
        <property name="driverClassName" value="${jdbc.Driver}"/>
        <property name="url" value="${jdbc.jdbcUrl}"/>
        <property name="username" value="${jdbc.user}"/>
        <property name="password" value="${jdbc.password}"/>
    </bean>

    <bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
        <property name="dataSource" ref="dataSource"/>
    </bean>

    <tx:annotation-driven proxy-target-class="false" transaction-manager="transactionManager" />

    <bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
        <property name="dataSource" ref="dataSource"/>
    </bean>

    <!--导入mapper-->
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="basePackage" value="service.blog.mybatis.mapper"/>
        <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"/>
    </bean>

    <!--配置mybatis配置文件-->
    <!--配置sqlmapper.xml配置文件-->
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource"/>
        <property name="configLocation" value="classpath:/mybatis-config.xml"/>
        <property name="mapperLocations" value="classpath:com/blog/mybatis/mapper/*.xml"/>
    </bean>

    <bean id="sqlSessionTemplate" class="org.mybatis.spring.SqlSessionTemplate">
        <constructor-arg index="0" ref="sqlSessionFactory"/>
        <constructor-arg index="1" value="BATCH"/>
    </bean>

</beans>

User user = service.selectUser(); 这里为null说明service没有自动装入

ssm? 你的xml为什么是这样的 注入失败

查看是否开启注解扫描， xml配置文件中是否配置了自动注入

把serviceimpl中的Autowired换成true