Spring IOC&DI 通过注解配置bean

组件扫描(component scanning): Spring 能够从 classpath 下自动扫描, 侦测和实例化具有特定注解的组件.
特定组件包括:
@Component: 基本注解, 标识了一个受 Spring 管理的组件
@Respository: 一般标识持久层组件
@Service: 一般标识服务层(业务层)组件
@Controller: 一般标识表现层组件

对于扫描到的组件, Spring 有默认的命名策略: 使用非限定类名, 第一个字母小写. 也可以在注解中通过 value 属性值标识组件的名称

如下代码示例：

使用@Component标识一个bean,在不知道这个bean是干什么的时候

@Component
public class Province {

    private int id;
    private String priviceNumber;
    private String priviceName;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getPriviceNumber() {
        return priviceNumber;
    }

    public void setPriviceNumber(String priviceNumber) {
        this.priviceNumber = priviceNumber;
    }

    public String getPriviceName() {
        return priviceName;
    }

    public void setPriviceName(String priviceName) {
        this.priviceName = priviceName;
    }

    public Province() {
    }

    public Province(int id, String priviceNumber, String priviceName) {
        this.id = id;
        this.priviceNumber = priviceNumber;
        this.priviceName = priviceName;
    }

    @Override
    public String toString() {
        return String.format("Province{id=%d, priviceNumber='%s', priviceName='%s'}", id, priviceNumber, priviceName);
    }
}

2. 一个普通的dao层

public interface ProvinceDao {
	public void say();
}

import com.dadi.dao.ProvinceDao;
import org.springframework.stereotype.Repository;

@Repository(value = "provinceDao")
public class ProvinceDaoImpl implements ProvinceDao {
	@Override
	public void say() {
		System.out.println("ProvinceDaoImpl...say");
	}
}

3. 一个普通的servicen层：@Autowired注解相当于对应的属性创建了一个set方法

public interface ProvinceService {
	public void say();
}

import com.dadi.dao.ProvinceDao;
import com.dadi.service.ProvinceService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service(value = "provinceService")
public class ProvinceServiceImpl implements ProvinceService {

	@Autowired
	private ProvinceDao provinceDao;

	@Override
	public void say() {
		System.out.println("ProviceServiceImpl...say进入");
		provinceDao.say();
	}
}

4.一个普通的controller层

@Controller
public class ControllerProvince {
	@Autowired
	private ProvinceService provinceService;
	public void say(){
		provinceService.say();
	}
}

5. spring的配置文件：applicationContext.xml，其中下面这个配置是自动扫描指定包下面的bean加载到IOC容器中的意思

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

<?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.xsd
       http://www.springframework.org/schema/context
       http://www.springframework.org/schema/context/spring-context.xsd">
    <!-- 自动扫描指定路径下面标注注解的bean -->
    <context:component-scan base-package="com.dadi"></context:component-scan>
</beans>

6. 测试方法

	@Test
	public void test() {
		ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");
		ControllerProvince controllerProvince = (ControllerProvince) ac.getBean("controllerProvince");
		controllerProvince.say();
		System.out.println("///////////////////////////////");
		String[] beanDefinitionNames = ac.getBeanDefinitionNames();
		Arrays.stream(beanDefinitionNames).forEach(System.out::println);
	}

7.运行结果

Spring IOC&DI 通过注解配置bean

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