官网地址： 1.8.3. Customizing Instantiation Logic with a FactoryBean

Core Technologieshttps://docs.spring.io/spring-framework/docs/5.2.22.RELEASE/spring-framework-reference/core.html#beans

概述

FactoryBean字面意思是工厂Bean。它就是起到一个工厂的作用。其getObject()方法可以生产另外一个对象，且生产的对象，也交由Spring容器管理。

通过FactoryBean的实现类，首字母小写，获得的是getObject返回的对象。在首字母小写前面加一个&符号，获得的是FactoryBean实例本身。

Spring提供了几个FactoryBean的实现类。用于在Spring的Bean中配置相应集合属性。

ListFactoryBean、MapFactoryBean、SetFactoryBean

示例代码

public class Computer {
    private String type;
    private String display;

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public String getDisplay() {
        return display;
    }

    public void setDisplay(String display) {
        this.display = display;
    }

    @Override
    public String toString() {
        return "Computer{" + "type='" + type + '\'' + ", display='" + display + '\'' + '}';
    }
}

/**
 * FactoryBean 的作用：通过ApplicationContext.getBean() 获取到的是Computer对象
 * 如果要获取Machine本身，在获取是用 & + id
 *
 * @see ListFactoryBean
 *
 */
public class Machine implements FactoryBean<Computer> {

    @Override
    public Computer getObject() throws Exception {
        Computer computer = new Computer();
        computer.setType("笔记本");
        computer.setDisplay("三星");
        return computer;
    }

    @Override
    public Class<?> getObjectType() {
        return null;
    }
}

public class FactoryBeanDemo {
    public static void main(String[] args) {
        // 加载context.xml
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("META-INF/context-factorybean.xml");
        Computer computer = context.getBean("machine", Computer.class);
        System.out.println(computer);
        //如果要获取Machine Bean本身
        Machine machine = context.getBean("&machine", Machine.class);
        System.out.println(machine);
    }
}

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

  <!-- bean definitions here -->
  <bean id="machine" class="org.xharvard.ioc.factorybean.Machine"/>
</beans>