MyBatis with Spring-配置错误空指针异常

Question

我是一个尝试整合mybatis的新手。最终出现了这个空指针异常。

我的POM

    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis-spring</artifactId>
        <version>1.1.1</version>
    </dependency>

我的Spring配置

<bean
    class="org.springframework.web.servlet.view.InternalResourceViewResolver">
    <property name="prefix">
        <value>/pages/</value>
    </property>
    <property name="suffix">
        <value>.jsp</value>
    </property>
</bean>

<context:component-scan base-package="biz.canisrigel.slapMe" />

<!-- enable autowire -->
<context:annotation-config />

<bean id="dataSource"
    class="org.springframework.jdbc.datasource.DriverManagerDataSource">
    <property name="driverClassName" value="com.mysql.jdbc.Driver" />
    <property name="url" value="jdbc:mysql://localhost/slapMe" />
    <property name="username" value="root" />
    <property name="password" value="adminadmin" />
</bean>

<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
    <property name="dataSource" ref="dataSource" />
    <property name="typeAliasesPackage" value="biz.canisrigel.slapMe.bean" />
</bean>

<!-- scan for mappers and let them be autowired -->
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
    <property name="basePackage" value="biz.canisrigel.slapMe.mapper" />
</bean>

我的地图绘制者

public interface UserMapper {

UserBean getUser();

}

<mapper namespace="biz.canisrigel.slapMe.mapper.UserMapper">

<select id="getUser" resultType="UserBean">
    Select * from Users where id = 1;
</select>

</mapper>

用户Bean

只是几个变量

我的DAO

@Service
public class UserDao {

@Autowired
private UserMapper userMapper;

public UserBean getUser(int id) {

    if (userMapper == null) {
        System.out.println("Errorrrrrr...................");
        // return new UserBean();
    }
    return userMapper.getUser();
}

}

控制器

@Controller
@RequestMapping("/authenticate")
public class LoginController {

@RequestMapping("/index")
public String index() {
    UserDao userDao = new UserDao();
    System.out.println(userDao.getUser(1).getPassword());
    return "Login";
}

}

错误

org.springframework.web.util.NestedServletExcture：请求处理失败；嵌套异常java.lang.NullPointerExctureorg.springframework.web.servlet.FrameworkServlet.process请求（FrameworkServlet.java:932）org.springframework.web.servlet.FrameworkServlet.do获取（FrameworkServlet.java:816）javax.servlet.http.HttpServlet.service（HttpServlet.java:621）

Answer 1

您的UserDao对象需要来自Spring对象存储以及映射器。像您这样在索引方法中实例化UserDao对象，意味着您在调用时映射器是null，因为Spring没有为您设置对象，因此无法自动连接映射器。

您需要使用@Resource注释将您的UserDao对象带到控制器中，如下所示：

 @Controller
 @RequestMapping("/authenticate")
 public class LoginController {

    @Resource
    UserDao userDao;

    @RequestMapping("/index")
    public String index() {
        System.out.println(userDao.getUser(1).getPassword());
        return "Login";
    }

 }