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目录结构

导入pom.xml依赖包

 <dependencies>
        <!-- https://mvnrepository.com/artifact/org.springframework/spring-webmvc -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>5.2.0.RELEASE</version>
        </dependency>

        <!--        aop-->
        <!-- https://mvnrepository.com/artifact/org.aspectj/aspectjweaver -->
        <dependency>
            <groupId>org.aspectj</groupId>
            <artifactId>aspectjweaver</artifactId>
            <version>1.9.19</version>
            <scope>runtime</scope>
        </dependency>

        <!-- https://mvnrepository.com/artifact/junit/junit -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.2</version>
            <scope>test</scope>
        </dependency>

    </dependencies>

People类，人可以有多个宠物

package com.qing;

public class People {

    private Cat cat;
    private Dog dog;

    private String name;

    public Cat getCat() {
        return cat;
    }

    public void setCat(Cat cat) {
        this.cat = cat;
    }

    public Dog getDog() {
        return dog;
    }

    public void setDog(Dog dog) {
        this.dog = dog;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "People{" +
                "cat=" + cat +
                ", dog=" + dog +
                ", name='" + name + ''' +
                '}';
    }
}

Cat类

package com.qing;

public class Cat {
    public void shout(){
        System.out.println("喵");
    }
}

Dog类

package com.qing;

public class Dog {
    public void shout(){
        System.out.println("汪");
    }
}

applicationContext.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"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
		https://www.springframework.org/schema/beans/spring-beans.xsd">


      <bean id="cat" class="com.qing.Cat"></bean>
      <bean id="dog" class="com.qing.Dog"></bean>

     <bean id="people" class="com.qing.People">
         <property name="name" value="你好呀"></property>
         <property name="cat" ref="cat"></property>
         <property name="dog" ref="dog"></property>

     </bean>


</beans>

测试代码

import com.qing.People;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MyTest {
    @Test
    public void test(){
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        People people = context.getBean("people", People.class);
        people.getDog().shout();
        people.getCat().shout();
    }
}

byName自动装配

 byName：会自动在容器上下文查找，和自己这个对象的set方法后面值对应的bean中的id

如果id不满足对象的名字，则会报错；例如：dog222不满足对象的id名字

byType自动装配

 byType：会自动在容器上下文中查找，和自己对象属性相同的bean，可以省略id

不能有两个一样的id，属性名可以不同

注解实现自动装配

导入约束，并开启注解的支持

<?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
		https://www.springframework.org/schema/beans/spring-beans.xsd
		http://www.springframework.org/schema/context
		https://www.springframework.org/schema/context/spring-context.xsd">

    <bean id="cat" class="com.qing.Cat"></bean>
    <bean id="dog" class="com.qing.Dog"></bean>
    <bean id="people" class="com.qing.People"></bean>
<!--    开启注解的支持-->
    <context:annotation-config/>

</beans>

在属性上配置注解

    @Autowired
    private Cat cat;
    @Autowired
    private Dog dog;

    private String name;

 如果@Autowired自动装配的环境比较复杂，自动装配无法通过一个注解@Autowired完成的时候，我们可以使用@Qualifier(value="xxx")去配置@Autowired的使用，指定一个唯一的bean对象注入

总结：

• byname需要保证所有的bean的id唯一，并且这个bean需要和自动注入的属性的set方法的值一致
• bytype需要保证所有bean的class唯一，并且这个bean需要和自动注入的属性类型一致