Official website address ： 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

summary

FactoryBean It literally means factory Bean. It just acts as a factory . Its getObject() Method can produce another object , And the object of production , It's up to you Spring Container management .

adopt FactoryBean Implementation class of , Initial lowercase , What you get is getObject Returned object . Add a... Before the initial lowercase & Symbol , What you get is FactoryBean The instance itself .

Spring There are several FactoryBean Implementation class of . Used in Spring Of Bean Configure the corresponding set properties .

ListFactoryBean、MapFactoryBean、SetFactoryBean

Sample code

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  The role of ： adopt ApplicationContext.getBean()  What you get is Computer object 
 *  If you want to get Machine In itself , Used when obtaining  & + id
 *
 * @see ListFactoryBean
 *
 */
public class Machine implements FactoryBean<Computer> {

    @Override
    public Computer getObject() throws Exception {
        Computer computer = new Computer();
        computer.setType(" The notebook ");
        computer.setDisplay(" samsung ");
        return computer;
    }

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

public class FactoryBeanDemo {
    public static void main(String[] args) {
        //  load context.xml
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("META-INF/context-factorybean.xml");
        Computer computer = context.getBean("machine", Computer.class);
        System.out.println(computer);
        // If you want to get Machine Bean In itself 
        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>