Spring学习总结(8)-接口多个实现类的动态调用

需求描述：当一个接口有2个以上的实现类时，调用方需要根据参数选择只其中一个实现类

Spring版本：5.1.8.RELEASE

1. 接口和实现类

/**
 * 接口
 */
public interface OrderInfoDao {

    void queryOrderList();
}

/**
 * 实现类A
 */
@Component
public class OrderInfoDaoAImpl implements OrderInfoDao {

    @Override
    public void queryOrderList() {
        System.out.println("Dao A queryOrderList");
    }
}

/**
 * 实现类B
 */
@Component
public class OrderInfoDaoBImpl implements OrderInfoDao {

    @Override
    public void queryOrderList() {
        System.out.println("Dao B queryOrderList");
    }
}

　　现在要求Service层要根据参数输入A或B动态选择实现类。

2. 使用ApplicationContextAware接口实现

@Component
public class OrderInfoServiceImpl implements ApplicationContextAware {

    private ApplicationContext applicationContext;

    public void query(String username){
        OrderInfoDao dao = null;
        if("A".equals(username)){
            dao = (OrderInfoDao) applicationContext.getBean("orderInfoDaoAImpl");
        }
        else if("B".equals(username)){
            dao = (OrderInfoDao) applicationContext.getBean("orderInfoDaoBImpl");
        }
        dao.queryOrderList();
    }

    /**
     * ApplicationContextAware接口的实现类，可以拿到上下文
     * @param applicationContext
     * @throws BeansException
     */
    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }
}

3. 使用@Autowired注入Map实现

@Component
public class OrderInfoServiceImpl {

    /**
     * 用这个方式Spring会在初始化时，自动把OrderInfoDao接口的实现类，全放到Map里
     */
    @Autowired
    private Map<String, OrderInfoDao> map;

    public void query(String username){
        // 拼接Dao实现类的名称
        String daoName = "orderInfoDao" + username + "Impl";
        OrderInfoDao dao = map.get(daoName);
        if(dao != null){
            dao.queryOrderList();
        }
    }

}

4. 测试

public class OrderInfo1Test {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
        OrderInfoServiceImpl service = context.getBean(OrderInfoServiceImpl.class);
        service.query("B");
    }

}