二、通過工廠方法來配置bean

調用靜態工廠方法創建 Bean是將對象創建的過程封裝到靜態方法中. 當客戶端需要對象時, 只需要簡單地調用靜態方法, 而不同關心創建對象的細節.
要聲明通過靜態方法創建的 Bean, 需要在 Bean 的 class 屬性里指定擁有該工廠的方法的類, 同時在 factory-method 屬性里指定工廠方法的名稱. 最后, 使用 <constrctor-arg> 元素為該方法傳遞方法參數.

實例工廠方法: 將對象的創建過程封裝到另外一個對象實例的方法里. 當客戶端需要請求對象時, 只需要簡單的調用該實例方法而不需要關心對象的創建細節.
要聲明通過實例工廠方法創建的 Bean
在 bean 的 factory-bean 屬性里指定擁有該工廠方法的 Bean
在 factory-method 屬性里指定該工廠方法的名稱
使用 construtor-arg 元素為工廠方法傳遞方法參數

<?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">
    <!--
        通過靜態工廠方法來配置bean，注意不是配置靜態工廠實例，而是配置bean實例
        class:指向靜態工廠的全類名
        factory-method:指向靜態工廠方法的名字
        constructor-arg:如果靜態工廠方法需要傳入參數，則使用constructor-arg來配置參數
    -->
    <bean id="car1" class="com.xiya.spring.beans.factory.StaticCarFactory" factory-method="getCar">
        <constructor-arg value="Ford"/>
    </bean>

    <!--配置工廠的實例-->
    <bean id="instanceCarFactory" class="com.xiya.spring.beans.factory.InstanceCarFactory"/>
    <!--
        通過實例工廠方法來配置bean
        factory-bean:指向實例工廠的bean
    -->
    <bean id="car2" factory-bean="instanceCarFactory" factory-method="getCar">
        <constructor-arg value="BMW"/>
    </bean>
</beans>

package com.xiya.spring.beans.factory;

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

/**
 * 實例工廠方法：實例工廠的方法，即需要先創建工廠本身，再調用工廠的實例方法來返回bean實例
 * Created by N3verL4nd on 2017/3/20.
 */
public class InstanceCarFactory {private Map<String, Car> cars;

    public InstanceCarFactory() {cars = new HashMap<>();
        cars.put("audi", new Car("audi", 300000));
        cars.put("BMW", new Car("BMW", 500000));
        cars.put("Ford", new Car("Ford", 200000));
    }public Car getCar(String brand) {return cars.get(brand);
    }
}

package com.xiya.spring.beans.factory;

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

/**
 * 靜態工廠方法：直接調用一個類的靜態方法就可以返回 bean 的實例
 * Created by N3verL4nd on 2017/3/20.
 */
public class StaticCarFactory {private static Map<String, Car> cars = new HashMap<>();

    static {cars.put("audi", new Car("audi", 300000));
        cars.put("BMW", new Car("BMW", 500000));
        cars.put("Ford", new Car("Ford", 200000));
    }//靜態工廠方法
    public static Car getCar(String brand) {return cars.get(brand);
    }public static void main(String[] args) {}
}

package com.xiya.spring.beans.factory;

/**
 * Created by N3verL4nd on 2017/3/20.
 */
public class Car {private String brand;
    private int price;

    public Car() {}public Car(String brand, int price) {this.brand = brand;
        this.price = price;
    }public String getBrand() {return brand;
    }public void setBrand(String brand) {this.brand = brand;
    }public int getPrice() {return price;
    }public void setPrice(int price) {this.price = price;
    }@Override
    public String toString() {return "Car{" +"brand='" + brand + '\'' +", price=" + price +'}';
    }
}

package com.xiya.spring.beans.factory;

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

/**
 * Created by N3verL4nd on 2017/3/20.
 */
public class Main {public static void main(String[] args) {ApplicationContext context = new ClassPathXmlApplicationContext("beans-factory.xml");
        Car car1 = (Car) context.getBean("car1");
        System.out.println(car1);

        Car car2 = (Car) context.getBean("car2");
        System.out.println(car2);
    }
}

輸出：

Car{brand='Ford', price=200000}
Car{brand='BMW', price=500000}