spring容器扩展之FactoryBean

                        Spring容器扩展之FactoryBean

      FactoryBean接口是Spring IoC容器实例化逻辑的扩展点。

一、区别FactoryBean和BeanFactory

首先不要混淆FactoryBean和BeanFactory。 
BeanFactory直译是生产Bean的工厂，在Srping中就是容器，常用的ApplicationContext就是它的一个继承类。我们也可以直接使用BeanFactory示例：

BeanFactory factory = new XmlBeanFactory(new FileSystemResource("/psring-config.xml"));

而FactoryBea只是一个bean，只不过比较特殊

二、区别FactoryBean和普通Bean

Spring中有两种类型的Bean，一种是普通Bean，另一种是工厂Bean即FactoryBean，这两种Bean都被容器管理。 
工厂Bean是实现了org.springframework.beans.factory.FactoryBean<T>接口的Bean，从ApplicationContext的getBean()方法获取的对象不是该类的一个实例，而是该类的getObject()方法所返回的对象。

当我们需要获取FactoryBean实例本身而不是它所产生的bean，则要使用&符号。 
比如，现有FactoryBean，id为”myBean”，在容器上调用getBean("myBean")将返回FactoryBean产生的bean。调用getBean("&myBean")将返回FactoryBean它本身的实例。

例如：如果使用传统方式配置下面Car的<bean>时，Car的每个属性分别对应一个<property>元素标签。

package com.spring.model;

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

如果用FactoryBean的方式实现就会灵活一些，下例通过逗号分割符的方式一次性地为Car的所有属性指定配置值：

public   class  CarFactoryBean  implements  FactoryBean<Car>  {    
    private  String carInfo ;    
    public  Car getObject ()   throws  Exception  {    
        Car car =  new  Car () ;    
        String []  infos =  carInfo .split ( "," ) ;    
        car.setBrand ( infos [ 0 ]) ;    
        car.setMaxSpeed ( Integer. valueOf ( infos [ 1 ])) ;    
        car.setPrice ( Double. valueOf ( infos [ 2 ])) ;    
        return  car;    
    }    
    public  Class<Car> getObjectType ()   {    
        return  Car. class ;    
    }    
    public   boolean  isSingleton ()   {    
        return   false ;    
    }    
    public  String getCarInfo ()   {    
        return   this . carInfo ;    
    }    
    
    // 接受逗号分割符设置属性信息    
    public   void  setCarInfo ( String carInfo )   {    
        this . carInfocarInfo  = carInfo;    
    }    
}

package com.spring.main;

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

import com.spring.model.Car;
import com.spring.model.Person;
import com.spring.model.Student;

public class Demoapp {

	public static void main(String[] args) {

		// Reading configuration from the spring configuration file.
		ConfigurableApplicationContext   context = new ClassPathXmlApplicationContext("spring-config.xml");

//		Person myperson = context.getBean("personBean", Person.class);
//		Student student = context.getBean("student", Student.class);
//		System.out.println("student id= " + student.getId());
//		System.out.println("Name= " + myperson.getName());
		Car car = context.getBean("car", Car.class);
		System.out.println("[car]"+car.toString());
		// Closing the context object.
		context.close();
	}
}

xml配置

	<bean id="car" class="com.spring.bean.CarFactoryBean">
	 	<property name="carInfo" value=" 超级跑车,400,2000000"></property>
	</bean>

输出如下：

Constructor of person bean is invoked!
Bean 'personBean' before created : com.spring.model.Person@7cd62f43
Initializing method of person bean is invoked!
Custom initializing method of person bean is invoked!
Bean 'personBean' created : com.spring.model.Person@7cd62f43
Bean 'student' before created : com.spring.model.Student@6d4b1c02
Bean 'student' created : com.spring.model.Student@6d4b1c02
Bean 'car' before created : com.spring.bean.CarFactoryBean@4667ae56
Bean 'car' created : com.spring.bean.CarFactoryBean@4667ae56
Bean 'car' created : Car [maxSpeed=400, brand= 超级跑车, price=2000000.0]
[car]Car [maxSpeed=400, brand= 超级跑车, price=2000000.0]
Destroy method of person bean is invoked!
Custom destroy method of person bean is invoked!