@Autowired注解是通过匹配数据类型自动装配Bean

创建Customer.java，可以给属性person、带person的构造器、setPerson方法任意一个标记@Autowired

package com.Re.autowiredDemo;

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

public class Customer {

    //新增一个adress参数
    private Address address;

    //给person使用@Autowired装配
    @Autowired
    private Person person;


    //无参构造
    public Customer() {
    }

    //带参构造
    public Customer(Person person) {
        this.person = person;
    }

    public Customer(Address address) {
        this.address = address;
    }
    
    public void setPerson(Person person) {
        this.person = person;
    }

    public void setAddress(Address address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "Customer{" +
                "address=" + address +
                ", person=" + person +
                '}';
    }
}

创建Person.java

package com.Re.autowiredDemo;

public class Person {
    private String hei;
    private String hi;

    public String getHei() {
        return hei;
    }

    public void setHei(String hei) {
        this.hei = hei;
    }

    public String getHi() {
        return hi;
    }

    public void setHi(String hi) {
        this.hi = hi;
    }

    @Override
    public String toString() {
        return "Person{" +
                "hei='" + hei + '\'' +
                ", hi='" + hi + '\'' +
                '}';
    }
}

创建测试文件Test.java

package com.Re.autowiredDemo;

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

public class Test {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("spring-config.xml");
        Customer customer = (Customer) context.getBean("customer");
        System.out.println(customer);
    }
}

编辑配置文件“spring-config.xml”

<?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">
    <!--指定文件路径-->
    <bean id="helloBean" class="com.Re.beanDemo.HelloSpring">
        <!--通过property给参数赋值 -->
        <property name="name" value="Re"/>
    </bean>

    <!--&lt;!&ndash;默认方式装配，有两个bean：customer和person-->
        <!--property name="person"指向Customer.setPerson方法-->
        <!--ref="person"指向"<bean id="person" class="com.Re.autowiredDemo.Person"/>"&ndash;&gt;-->
    <!--<bean id="customer" class="com.Re.autowiredDemo.Customer">-->
        <!--<property name="person" ref="person"/>-->
    <!--</bean>-->

    <!--<bean id="person" class="com.Re.autowiredDemo.Person">-->
        <!--&lt;!&ndash;将“hello”赋值给参数“hei”&ndash;&gt;-->
        <!--<property name="hei" value="hello"/>-->
    <!--</bean>-->

    <!--&lt;!&ndash;byName方式自动装配&ndash;&gt;-->
    <!--<bean id="customer" class="com.Re.autowiredDemo.Customer" autowire="byName"/>-->

    <!--<bean id="address2" class="com.Re.autowiredDemo.Address">-->
        <!--<property name="myaddress" value="杭州西湖"/>-->
    <!--</bean>-->


    <!--&lt;!&ndash;通过类型自动装配&ndash;&gt;-->
    <!--<bean id="customer" class="com.Re.autowiredDemo.Customer" autowire="byType"/>-->

    <!--<bean id="address2" class="com.Re.autowiredDemo.Address">-->
        <!--<property name="myaddress" value="杭州余杭"/>-->
    <!--</bean>-->


    <!--这一行配置是启用@Autowired
        也可用<bean class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor"/>-->
    <context:annotation-config/>
    <!--通过@Autowired自动装配-->
    <bean id="customer" class="com.Re.autowiredDemo.Customer"/>
    <bean id="person" class="com.Re.autowiredDemo.Person">
        <property name="hei" value="hello autowired"/>
    </bean>



</beans>

项目结构

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注释掉配置文件里person的配置
会报错，原因是@Autowired会检查属性已经装配正常。当Spring无法找到匹配的Bean装配，就会报错。
可以通过 @Autowired 的“required”属性设置为false来禁用此检查功能。

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如果有多个person bean配置，那么要用@Qualifier注解指定使用哪个bean

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参考：https://www.yiibai.com/spring