Spring学习--实现 FactoryBean 接口在 Spring IOC 容器中配置 Bean

Spring 中有两种类型的 bean , 一种是普通的 bean , 另一种是工厂 bean , 即 FactroyBean。

工厂 bean 跟普通 bean 不同 , 其返回的对象不是指定类的一个实例 , 其返回的是该工厂 bean 的 getObject 方法所返回的对象。

 <?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.itdjx.spring.factorybeans.CarFactoryBean">
         <property name="name" value="BMW"/>
     </bean>

 </beans>

 package com.itdjx.spring.factorybeans;

 /**
  * @author Wáng Chéng Dá
  * @create 2017-03-03 8:08
  */
 public class Car {

     private String name;

     private int price;

     public int getPrice() {
         return price;
     }

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

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }

     public Car(String name, int price) {
         this.name = name;
         this.price = price;
     }

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

 package com.itdjx.spring.factorybeans;

 import org.springframework.beans.factory.FactoryBean;

 /**
  * @author Wáng Chéng Dá
  * @create 2017-03-03 8:10
  */
 public class CarFactoryBean implements FactoryBean {

     private String name;

     public void setName(String name) {
         this.name = name;
     }

     @Override //factoryBean 返回的实例
     public Object getObject() throws Exception {
         System.out.println("I am CarFactoryBean's getObject method...");
         return new Car(name, 500000);
     }

     @Override //factoryBean 返回的类型
     public Class<?> getObjectType() {
         System.out.println("I am CarFactoryBean's getObjectType method...");
         return Car.class;
     }

     @Override //返回的实例是否为单例
     public boolean isSingleton() {
         System.out.println("I am CarFactoryBean's isSingleton method...");
         return true;
     }
 }

 package com.itdjx.spring.factorybeans;

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

 /**
  * @author Wáng Chéng Dá
  * @create 2017-03-03 8:14
  */
 public class Main {

     public static void main(String[] args) {

         ApplicationContext cxt = new ClassPathXmlApplicationContext("factory-beans.xml");
         Car car = (Car) cxt.getBean("car");
         System.out.println(car);

     }
 }

控制台输出：

I am CarFactoryBean's isSingleton method...
I am CarFactoryBean's getObjectType method...
I am CarFactoryBean's isSingleton method...
I am CarFactoryBean's getObject method...
Car{name='BMW', price=500000}

创建 IOC 容器时调用 isSingleton 若是返回 true 调用 getObjectType , 若返回 false , IOC 直接创建完成。

创建 Car 实例时调用 isSingleton -->> getObject , 实例创建完成。