Sring 依赖注入

Spring 注入有构造注入和设值注入。
常用设置注入。

package com.shpun.dao 包下

BaseDao

package com.shpun.dao;
public interface BaseDao {
    void connectSql();
    void closeSql();
}

BaseDaoImpl

package com.shpun.dao;
public class BaseDaoImpl implements BaseDao {
    
    @Override
    public void connectSql() {
        System.out.println("connect mysql");
    }

    @Override
    public void closeSql() {
        System.out.println("close mysql");
    }
}

CustomerDao

package com.shpun.dao;
public interface CustomerDao {
    void queryAllCustomers();
}

CustomerDaoImpl

package com.shpun.dao;
public class CustomerDaoImpl implements CustomerDao {

    private BaseDao baseDao;

    // 设值注入
    public void setBaseDao(BaseDao baseDao) {
        this.baseDao = baseDao;
    }

    @Override
    public void queryAllCustomers() {
        baseDao.connectSql();
        System.out.println("queryAllCustomers success");
        baseDao.closeSql();
    }
}

package com.shpun.service 下

ActivityService

package com.shpun.service;
public interface ActivityService {
    void joinActivity();
}

ActivityServiceImpl

package com.shpun.service;
public class ActivityServiceImpl implements ActivityService {

    private CustomerDao customerDao;

    // 构造注入
    public ActivityServiceImpl(CustomerDao customerDao){
        this.customerDao = customerDao;
    }

    @Override
    public void joinActivity() {
        System.out.println("查询愿意活动客户 : ");
        customerDao.queryAllCustomers();
        System.out.println("以上客户参加活动");
    }

    public static void main(String[] args){

        ApplicationContext context = new ClassPathXmlApplicationContext("classpath:spring-config.xml");

        ActivityServiceImpl activityServiceImpl = context.getBean("activityServiceImpl",ActivityServiceImpl.class);
        activityServiceImpl.joinActivity();
    }
}

spring-config.xml

    <bean id="baseDaoImpl" class="com.shpun.dao.BaseDaoImpl"/>
    <bean id="customerDaoImpl" class="com.shpun.dao.CustomerDaoImpl">
        <!-- CustomerDaoImpl中依赖BaseDaoImpl，使用标签property进行设值注入 
          name要和CustomerDaoImpl中要一致 ref为要注入的Bean
        -->
        <property name="baseDao" ref="baseDaoImpl"/>
    </bean>
    <bean id="activityServiceImpl" class="com.shpun.service.ActivityServiceImpl">
    <!-- ActivityServiceImpl依赖CustomerDaoImpl，进行构造注入 -->        
        <constructor-arg name="customerDao" ref="customerDaoImpl"/>
    </bean>

显示结果

查询愿意活动客户 : 
connect mysql
queryAllCustomers success
close mysql
以上客户参加活动

若A类需要依赖其他类B，C，D，则在类A内实现B，C，D的set方法，在配置文件中加property，进行设值注入；或在构造器中进行构造注入。

要使用注解的方式，需要在配置文件加上：

<!--
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd"
-->
        
<!-- 自动扫描con.shpun以及子包下所有的Bean -->
<context:component-scan base-package="com.shpun"></context:component-scan>

BaseDaoImpl 类定义上加上 @Repository
CustomerDaoImpl 类定义上加上 @Repository ，set方法上加上@Autowired
ActivityServiceImpl 类定义上加上 @Service，构造器上加上@Autowired