@Autowired 注释返回 null [英] @Autowired annotation returns null

问题描述

当我在 Spring Framework 中开发时，我想在特定类上使用 mybatis 来访问 DB，这是问题.

When I develop in the Spring Framework, I wanted to get an access to DB using mybatis on the specific class, here is problem.

     public class ScheduleManager {

            private Scheduler scheduler;

            @Autowired
            private TriggerService triggerService;

            public void doit() {

                    System.out.println(triggerService);

            }

        }

这里，triggerService 的值为空.我认为 triggerService 不是自动装配的.

At here, value of triggerService is null. I think triggerService was not autowired.

但它是在这个类中自动装配的.

But it is autowired at this class.

 @Controller
    public class TestController {

        @Autowired
        private TriggerService triggerService;

        @RequestMapping("/scheduletest")
        public String scheduleTest() {

            System.out.println(triggerService);

            ScheduleManager sm = new ScheduleManager();

            sm.doit();
        }
    }

此代码打印一些非空值.

this code print some value not null.

dispatcher-servlet.xml

dispatcher-servlet.xml

<?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:context="http://www.springframework.org/schema/context"

       xsi:schemaLocation="http://www.springframework.org/schema/beans
             http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
             http://www.springframework.org/schema/context
             http://www.springframework.org/schema/context/spring-context-3.0.xsd">

    <context:annotation-config/>

    <context:component-scan base-package="com.scheduler"/>

    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/views/"/>
        <property name="suffix" value=".jsp"/>
        <property name="contentType" value="text/html;charset=UTF-8"/>
        <property name="order" value="0"/>
    </bean>

</beans>

TriggerService 接口

TriggerService interface

@Service
public interface TriggerService {
    public List<Trigger> getAll();
}

为什么会出现这个问题?

Why does this problem appear?

推荐答案

您自己创建 ScheduleManager 实例:

You create the ScheduleManager instance by yourself:

ScheduleManager sm = new ScheduleManager();

所以 Spring 不知道这个对象，也不做任何自动装配.要解决此问题，请将 @Component 注释添加到 ScheduleManager 并让它也注入控制器:

So Spring doesn't know about this object and doesn't do any autowiring. To resolve this, add the @Component annotation to ScheduleManager and let it also inject in the controller:

@Autowired
private ScheduleManager scheduleManager;

这篇关于@Autowired 注释返回 null的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！