spring学习笔记三:Component注解(把POJO类实例化到spring的IOC容器中)

Component注解:把普通的POJO 类实例化到spring的IOC容器中,就是定义成<bean id="" class="">

项目目录树:

ApplicationContext.xml

<beans xmlns="http://www.springframework.org/schema/beans"  
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  
    xmlns:aop="http://www.springframework.org/schema/aop"  
    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/aop  
       http://www.springframework.org/schema/aop/spring-aop-3.0.xsd  
       http://www.springframework.org/schema/context  
       http://www.springframework.org/schema/context/spring-context-3.0.xsd" 
        >  
    <!-- component-scan 会自动开启bean自动注册,base-package会扫描该包下的特殊注解 -->
    <context:component-scan base-package="com.donghai.bean" />
    
</beans>

User.java

package com.donghai.bean;

import org.springframework.stereotype.Component;

@Component("user") //使用Component注解,相当于添加<bean id="user" class="com.donghai.bean.User" />
public class User {

    private String name = "ddh";
    
    public String getName() {
        return name;
    }

    
}

Group.java

package com.donghai.bean;

import javax.annotation.Resource;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Component("group")
public class Group {

    @Autowired  //使用自动装配,默认按照byType对应的类型查找bean,如果只有一个注入,如果有多个抛出异常
Caused by: org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type
需要使用@Qualifier(" ") 来指定使用那个实现
,也可以使用Resource(name="user") 使用资源指定
    private User user;

    public User getUser() {
        return user;
    }
    
    
}

Client.java

package com.donghai.spring;


import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.donghai.bean.Group;
import com.donghai.bean.User;

public class Client {

    public static void main(String[] args){
        ApplicationContext acc = new ClassPathXmlApplicationContext("applicationContext.xml");
        Group group = (Group)acc.getBean("group");
        System.out.println(group.getUser().getName());
    }
}

运行结果: