Spring依赖注入的两种方式(set方法和构造器)_private usermapper usermapper;

个人对依赖和注入的理解

依赖:一个bean的内部含有其他bean,这个bean依赖于内部的bean运行

注入:对一个bean内部的bean进行注入

1.set方法注入

实现类源码:

public class UserMapperImpl implements UserMapper {
 
    @Override
    public void save() {
        System.out.println("user mapper save()...");
    }
}

public class UserServiceImpl implements UserService {
    private UserMapper userMapper;
 
    @Override
    public void save() {
        System.out.println("user service impl save()...");
        userMapper.save();
    }
 
    //需要对进行依赖注入的类中提供被注入对象对应的set方法
    public void setUserMapper(UserMapper userMapper) {
        this.userMapper = userMapper;
    }
 
}

xml配置:

<!--
    property中的name属性为UserServiceImpl中setUserMapper方法去掉set字母的小驼峰命名
    ref属性为当前xml配置文件中bean的id
-->
<bean id="userMapper" class="com.nf.mapper.impl.UserMapperImpl"/>
<bean id="userService" class="com.nf.service.impl.UserServiceImpl">
    <property name="userMapper" ref="userMapper"/>
</bean>

2.构造器注入

xml配置:

<bean id="userMapper" class="com.nf.mapper.impl.UserMapperImpl"/>
<!--
    <constructor-arg/>:表示使用构造器进行注入
    name属性为构造器参数上的名称
    ref属性为xml配置文件中bean的id
-->
<bean id="userService" class="com.nf.service.impl.UserServiceImpl">
    <constructor-arg name="userMapper" ref="userMapper"/>
</bean>

测试类:

public class App {
    public static void main(String[] args) {
        //加载配置文件,获取上下文对象
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");  
        //获取bean
        UserService userService = (UserService) applicationContext.getBean("userService");
        userService.save();
    }
}

(如有错误,请指正)