二、Spring-Bean的自动装配

Bean的自动装配定义：在Spring配置文件不需要配置JavaBean之间的依赖关系，如 property、constructor-arg

• Spring IOC容器可以在上下文中自动寻找，实现自动装配Bean。
• 在Spring中有三种装配方式：xml中配置、java中配置、隐式的自动装配(重要)

1.创建实体类

三个实体类：Goods(商品)、Providers(供应商)、Brands(品牌)

package com.yy.pojo;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import java.math.BigDecimal;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Goods {
    private String goodID;
    private String goodName;
    private String goodType;
    //品牌
    private Brands brand;
    private BigDecimal cost;
    //供应商
    private Providers provider;

    public Goods(String goodID, String goodName) {
        this.goodID = goodID;
        this.goodName = goodName;
    }
}

package com.yy.pojo;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Providers {
    private String providerID;
    private String providerName;
    private String address;
    private String tel;
}

package com.yy.pojo;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Brands {
    private String brandID;
    private String brandName;
}

2.创建Bean.xml

在xml中配置

<?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="provider" class="com.yy.pojo.Providers">
        <property name="address" value="zj"></property>
        <property name="providerID" value="p001"></property>
        <property name="providerName" value="小h"/>
        <property name="tel" value="13812355581"/>
    </bean>
    <bean id="brand" class="com.yy.pojo.Brands">
        <property name="brandID" value="b001"/>
        <property name="brandName" value="sevenRB"/>
    </bean>
    <bean id="goods" class="com.yy.pojo.Goods">
        <property name="goodID" value="z001"/>
        <property name="goodName" value="主板"/>
        <property name="cost" value="2000"/>
        <property name="goodType" value="硬件"/>
        <property name="brand" ref="brand"/>
        <property name="provider" ref="provider"/>
    </bean>

</beans>

3.测试类

import com.yy.pojo.Goods;
import org.junit.jupiter.api.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class BeanTest {
    @Test
    public void myTest(){
        ApplicationContext context = new ClassPathXmlApplicationContext("AplicationContext.xml") ;
        Goods goods = context.getBean("goods", Goods.class);
        System.out.println(goods);
    }
}

• 通过ByName自动装配。
  ByName会自动在容器中上下文查找和自己对象的set方法后面的值对应的Bean的id，但需保证id是唯一的。

<bean id="goods" class="com.yy.pojo.Goods" autowire="byName">
        <property name="goodID" value="z001"/>
        <property name="goodName" value="主板"/>
        <property name="cost" value="2000"/>
        <property name="goodType" value="硬件"/>
    </bean>

• 通过ByType自动装配。
  ByType会自动在容器中上下文查找和自己对象属性类型相对应的Bean，但必须保证这个类型Class全局唯一。

<bean id="goods" class="com.yy.pojo.Goods" autowire="byType">
    </bean>

• 使用注解自动装配
  1.导入约束
  2.配置注解的支持context:annotation-config

<beans 
	xmlns:context="http://www.springframework.org/schema/context"
	xsi:schemaLocation="http://www.springframework.org/schema/context
        https://www.springframework.org/schema/context/spring-context.xsd">
	context:annotation-config /> //或者<component-scan />
</beans>

3.@Autowired
直接在属性或者Set方法上使用。

package com.yy.pojo;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.springframework.beans.factory.annotation.Autowired;

import java.math.BigDecimal;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Goods {
    private String goodID;
    private String goodName;
    private String goodType;
    //品牌
    @Autowired
    private Brands brand;
    private BigDecimal cost;
    //供应商
    //设置requiredw为false，则表示对象可以为null
    @Autowired(required = false)
    private Providers provider;

    public Goods(String goodID, String goodName) {
        this.goodID = goodID;
        this.goodName = goodName;
    }
}

通过@Qualifier(value="")注解可以配置@Autowired指定一个唯一的bean对象注入
@Resource注解同样可以实现，Java的原生注解。