spring 通过工厂方法配置Bean

• 实例工厂方法：将对象的创建过程封装到另外一个对象实例的方法里。当client须要请求对象时，仅仅须要简单的调用该实例方法而不须要关心对象的创建细节
• 要声明通过实例工厂方法创建的Bean
  • 在bean的factory-bean属性里指定拥有该工厂方法的Bean
  • 在factory-method属性里指定该工厂方法的名称
  • 使用construtor-arg元素为工厂方法传递方法參数

package com.coslay.beans.factory;

public class Car {
	private String brand;
	private double price;

	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 [brand=" + brand + ", price=" + price + "]";
	}

	public Car() {
		System.out.println("Car's Constructor...");
	}

	public Car(String brand, double price) {
		super();
		this.brand = brand;
		this.price = price;
	}

}

package com.coslay.beans.factory;

import java.util.HashMap;
import java.util.Map;

/*
 * 静态工厂方法：直接调用某一个类的静态方法就能够返回Bean的实例
 */
public class StaticCarFactory {
	
	private static Map<String,Car> cars = new HashMap<String,Car>();
	
	static{
		cars.put("audi", new Car("audi",300000));
		cars.put("ford", new Car("ford",400000));
	}
	
	//静态工厂方法
	public static Car getCar(String name){
		return cars.get(name);
	}
}

package com.coslay.beans.factory;

import java.util.HashMap;
import java.util.Map;


/*
 *实例工厂方法：实例工厂的方法，即先须要创建工厂本身，再调用工厂的实例方法来返回bean的实例 
 */
public class InstanceCarFactory {
	
	private Map<String,Car> cars =null;
	
	public InstanceCarFactory(){
		cars = new HashMap<String,Car>();
		cars.put("audi", new Car("audi",300000));
		cars.put("ford",new Car("ford",400000));
	}
	
	public Car getCar(String brand){
		return cars.get(brand);
	}
	
}

package com.coslay.beans.factory;

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

public class Main {
	public static void main(String[] args) {
		ApplicationContext ctx = new ClassPathXmlApplicationContext("beans-factory.xml");
		Car car1 = (Car) ctx.getBean("car1");
		System.out.println(car1);
		
		Car car2 = (Car) ctx.getBean("car2");
		System.out.println(car2);
	}
}

<?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">
	
	
	<!-- 通过静态工厂方法来配置bean，注意不是配置静态工厂方法实例，而是配置bean实例 -->
	<!-- 
		class属性：指向静态工厂方法的全类名
		factory-method：指向静态工厂方法的名字
		constructor-arg：假设工厂方法须要传入參数，则使用constructor-arg来配置參数
	 -->
	<bean id="car1" class="com.coslay.beans.factory.StaticCarFactory"
		factory-method="getCar">
		<constructor-arg value="audi"></constructor-arg>	
	</bean>
	
	<!-- 配置工厂的实例 -->
	<!-- 
		class属性：指向实例工厂方法的全类名
		factory-method：指向静态工厂方法的名字
		constructor-arg：假设工厂方法须要传入參数，则使用constructor-arg来配置參数
	 -->
	<bean id="carFactory" class="com.coslay.beans.factory.InstanceCarFactory"></bean>
	<!-- 通过实例工厂方法来配置bean -->
	<bean id="car2" factory-bean="carFactory" factory-method="getCar">
		<constructor-arg value="ford"></constructor-arg>
	</bean>
</beans>