Spring 源码学习(2) —— FactoryBean 的使用

一般情况下, Spring是通过反射机制利用bean的class属性指定实现类来完成实例化bean的。在某些特定的情况下, 想做一些定制，Spring为此提供了一个org.springframework.beans.factory.FactoryBean的工厂类接口, 用户可以通过实现该接口定制实例化bean的逻辑。

Spring从3.0开始, FactoryBean开始支持泛型, 即接口声明改为: FactoryBean<T> 的形式。

 package org.springframework.beans.factory;

 public interface FactoryBean<T> {

     /**
      *
      * @return 返回由FactoryBean创建的bean实例, 如果isSingleton()返回true, 则该实例则会放到Spring容器单实例缓存池中
      * @throws Exception
      */
     T getObject() throws Exception;

     /**
      *
      * @return 返回FactoryBean创建Bean的类型
      */
     Class<?> getObjectType();

     /**
      *
      * @return 返回有FactoryBean创建的bean实例的作用域是singleten还是prototype
      */
     boolean isSingleton();
 }

Action

创建一个pojo类<Car>。

 /**
  * @filename: Car.java
  * @author: Wang Chinda
  * @date: 2018-05-22
  * @version: v1.0
  * @modify_history: -
  * 20180522   Wang Chinda   create
  * 20180522   Wang Chinda   modify   method()
  */
 package com.itdoc.learn.source.factory;

 /**
  * @desc FactoryBean 的使用
  * @author Wang Chinda
  * @create 2018-05-22 16:07
  */
 public class Car {
     /** 最大速度 */
     private int maxSpeed;
     /** 品牌 */
     private String brand;
     /** 价钱 */
     private double price;

     public int getMaxSpeed() {
         return maxSpeed;
     }

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

     public String getBrand() {
         return brand;
     }

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

     public double getPrice() {
         return price;
     }

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

     @Override
     public String toString() {
         return "Car{" +
                 "maxSpeed=" + maxSpeed +
                 ", brand='" + brand + '\'' +
                 ", price=" + price +
                 '}';
     }
 }

创建一个定制实例化bean逻辑的类<CarFactoryBean>:

 /**
  * @filename: CarFactoryBean.java
  * @author: Wang Chinda
  * @date: 2018-05-22
  * @version: v1.0
  * @modify_history: -
  * 20180522   Wang Chinda   create
  * 20180522   Wang Chinda   modify   method()
  */
 package com.itdoc.learn.source.factory;

 import org.springframework.beans.factory.FactoryBean;

 /**
  * @desc FactoryBean测试的工厂类
  * @author Wang Chinda
  * @create 2018-05-22 16:17
  */
 public class CarFactoryBean implements FactoryBean<Car> {

     /** 车的详细信息 */
     private String carInfo;

     @Override
     public Car getObject() throws Exception {
         Car car = new Car();
         String[] infos = carInfo.split(",");
         car.setBrand(infos[0].trim());
         car.setMaxSpeed(Integer.valueOf(infos[1].trim()));
         car.setPrice(Double.valueOf(infos[2].trim()));
         return car;
     }

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

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

     public String getCarInfo() {
         return carInfo;
     }

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

配置xml<car-factory-bean.xml>:

 <?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 http://www.springframework.org/schema/beans/spring-beans.xsd">

     <bean id="car" class="com.itdoc.learn.source.factory.CarFactoryBean">
         <property name="carInfo" value="超级跑车, 400, 300000000"></property>
     </bean>

 </beans>

测试<Car>:

 /**
  * @filename: CarClient.java
  * @author: Wang Chinda
  * @date: 2018-05-22
  * @version: v1.0
  * @modify_history: -
  * 20180522   Wang Chinda   create
  * 20180522   Wang Chinda   modify   method()
  */
 package com.itdoc.learn.source.factory;

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

 /**
  * @desc FactoryBean使用测试客户端入口
  * @author Wang Chinda
  * @create 2018-05-22 16:27
  */
 public class CarClient {
     public static void main(String[] args) {
         ApplicationContext applicationContext = new ClassPathXmlApplicationContext("test/car-factory-bean.xml");
         Car car = (Car) applicationContext.getBean("car");
         System.out.println(car);
     }
 }

控制台打印：

流程分析：

当配置文件中<bean>的class属性配置类的实现类是FactoryBean时, 通过getBean返回的不是FactoryBean本身, 而是FactoryBean#getObject()方法返回的对象, 相当于FactoryBean#getObject()代理了getBean()方法。

从缓存中或者singletonFactories中的ObjectFactory中获取共享实例。

Object sharedInstance = getSingleton(beanName);

bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd); 获取对应实例。

强制将共享实例转化成FactoryBean。FactoryBean<?> factory = (FactoryBean<?>) beanInstance;

object = getObjectFromFactoryBean(factory, beanName, !synthetic); 在FactoryBean中获取bean实例。

doGetObjectFromFactoryBean(factory, beanName, shouldPostProcess);

调用getObject()方法，object = factory.getObject();

返回实例bean。

GitHub源码: https://github.com/wcd19901010/spring-01