Spring FactoryBean

spring编码方式实例化bean

一般情况下，Spring通过反射机制利用<bean>的class属性指定的实现类实例化bean，也可以通过java类或注解的方式实例化bean。

Spring还也提供了编码方式实例化bean。Spring为此提供了一个org.springframework.beans.factory.FactoryBean工厂类接口，可以通过实现该接口来实例化bean。org.springframework.beans.factory.FactoryBean接口对于Spring框架来说占有重要的地位，Spring自身就提供了70多个FactoryBean的实现类。

提示：在Spring中BeanFactory和FactoryBean是两个不同的接口

Demo

import org.springframework.beans.factory.FactoryBean;

public class CarFactoryBean implements FactoryBean<Car> {
    private String carInfo;

    public String getCarInfo() {
        return carInfo;
    }

    public void setCarInfo(String carInfo) {
        this.carInfo = carInfo;
    }

    /**
     * 将来调用getBean()方法返回的不是FactoryBean本身，而是getObject返回的Car
     * 也就是说下面这个getObjext方法会被getBean方法代理
     */
    public Car getObject() {
        Car car = new Car();
        String[] infos = carInfo.split(",");
        car.setBrand(infos[0]);
        car.setMaxSpeed(Integer.parseInt(infos[1]));
        car.setPrice(Double.parseDouble(infos[2]));
        return car;
    }

    @Override
    public Class<?> getObjectType() {
        return Car.class;
    }

    @Override
    public boolean isSingleton() {
        return false;
    }
}

class Car {
    private String brand;
    private int maxSpeed;
    private double price;

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }
}

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:p="http://www.springframework.org/schema/p"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="
      http://www.springframework.org/schema/beans
      http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="car" class="CarFactoryBean" p:carInfo="吉利博越,200,10000.50"/>

</beans>

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

public class Driver {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("my.xml");

        /**
         *  当调用getBean("car")时，Spring通过反射机制发现CarFactoryBean实现了FactoryBean的接口，
         *  Spring容器就调用CarFactoryBean的getObject返回Car对象
         */
        Car car = context.getBean("car", Car.class);
        System.out.println(car.getBrand());
        /**
         * 如果希望获得CarFactoryBean的实例，需要在加前缀 &
         */
        CarFactoryBean carFactoryBean = context.getBean("&car", CarFactoryBean.class);
        System.out.println(carFactoryBean);
    }
}

      <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-core</artifactId>
        <version>4.3.16.RELEASE</version>
      </dependency>
      <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version>4.3.16.RELEASE</version>
      </dependency>
      <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-beans</artifactId>
        <version>4.3.16.RELEASE</version>
      </dependency>