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。

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1 package com.itdjx.spring.factorybeans; 2  3 /** 4  * @author Wáng Chéng Dá 5  * @create 2017-03-03 8:08 6  */ 7 public class Car { 8  9     private String name;10 11     private int price;12 13     public int getPrice() {14         return price;15     }16 17     public void setPrice(int price) {18         this.price = price;19     }20 21     public String getName() {22         return name;23     }24 25     public void setName(String name) {26         this.name = name;27     }28 29     public Car(String name, int price) {30         this.name = name;31         this.price = price;32     }33 34     @Override35     public String toString() {36         return "Car{" +37                 "name='" + name + '\'' +38                 ", price=" + price +39                 '}';40     }41 }

1 package com.itdjx.spring.factorybeans; 2  3 import org.springframework.beans.factory.FactoryBean; 4  5 /** 6  * @author Wáng Chéng Dá 7  * @create 2017-03-03 8:10 8  */ 9 public class CarFactoryBean implements FactoryBean {10 11     private String name;12 13     public void setName(String name) {14         this.name = name;15     }16 17     @Override //factoryBean 返回的实例18     public Object getObject() throws Exception {19         System.out.println("I am CarFactoryBean's getObject method...");20         return new Car(name, 500000);21     }22 23     @Override //factoryBean 返回的类型24     public Class
      getObjectType() {25         System.out.println("I am CarFactoryBean's getObjectType method...");26         return Car.class;27     }28 29     @Override //返回的实例是否为单例30     public boolean isSingleton() {31         System.out.println("I am CarFactoryBean's isSingleton method...");32         return true;33     }34 }

1 package com.itdjx.spring.factorybeans; 2  3 import org.springframework.context.ApplicationContext; 4 import org.springframework.context.support.ClassPathXmlApplicationContext; 5  6 /** 7  * @author Wáng Chéng Dá 8  * @create 2017-03-03 8:14 9  */10 public class Main {11 12     public static void main(String[] args) {13 14         ApplicationContext cxt = new ClassPathXmlApplicationContext("factory-beans.xml");15         Car car = (Car) cxt.getBean("car");16         System.out.println(car);17 18     }19 }

 

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。