bean的自动装配

bean的自动装配

概述

自动装配是指Spring会自己在上下文中寻找并自动给bean装配属性
Spring有三种装配方式：

1. 使用xml显式配置
2. java显式配置
3. 隐式地自动装配bean[重要]

本文主要讲隐式自动装配bean

实践

基本代码： 一人拥有一猫一狗

猫类

package com.kuangstudy;

/**
 * 功能描述
 *
 * @since 2022-06-26
 */
public class Cat {
    public void shout() {
        System.out.println("miao~");
    }
}

狗类

package com.kuangstudy;

/**
 * 功能描述
 *
 * @since 2022-06-26
 */
public class Dog {
    public void shout() {
        System.out.println("wang~");
    }
}

人类

package com.kuangstudy;

/**
 * 功能描述
 *
 * @since 2022-06-26
 */
public class Person {
    private String name;
    private Cat cat;
    private Dog dog;

    public String getName() {
        return name;
    }

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

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

测试类

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

import com.kuangstudy.Person;

/**
 * 功能描述
 *
 * @since 2022-06-26
 */
public class Test02 {
    @Test
    public void test() {
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml");
        Person person = applicationContext.getBean("xiaohong", Person.class);
        person.getCat().shout();
        person.getDog().shout();
    }
}

装配配置

手动装配

<?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.kuangstudy.Cat"></bean>
    <bean id="dog" class="com.kuangstudy.Dog"></bean>
    <bean id="xiaohong" class="com.kuangstudy.Person">
        <property name="cat" ref="cat"></property>
        <property name="dog" ref="dog"></property>
    </bean>
</beans>

自动装配byName

<?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.kuangstudy.Cat"></bean>
    <bean id="dog" class="com.kuangstudy.Dog"></bean>
    <bean id="xiaohong" class="com.kuangstudy.Person" autowire="byName"></bean>
</beans>

自动装配byType

<?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 class="com.kuangstudy.Cat"></bean>
    <bean class="com.kuangstudy.Dog"></bean>
    <bean id="xiaohong" class="com.kuangstudy.Person" autowire="byType"></bean>
</beans>

总结

手动装配需要给person类手动配上bean类型的属性
自动装配byName可以寻找跟属性相同名称的bean自动完成装配，要求与属性名称相同的bean必须存在且唯一
自动装配byType可以寻找类型相同的bean自动完成装配，要求与属性类型相同的bean唯一