09 通过工厂方法配置Bean

Bean的配置方式,除了全类名(反射机制)之外,还可以通过**工厂方法(静态工厂方法&实例工厂方法)**以及FactoryBean的方式来配置

1. 通过调用静态工厂方法创建Bean

• 静态工厂方法:将对象创建的过程封装到静态方法中.当客户端需要对象时,只需要简单的调用静态方法,而不用关心创建对象的细节
• 要声明通过静态方法创建的Bean,需要在Bean的class属性里指定拥有该工厂的类,同时在factory-method属性里指定该工厂方法的名称.最后,使用<constructor-arg>元素为该方法传递方法参数

代码示例:

Car.java

package factory;/*
 * @Author Sheng WenZeng
 * @Date 2019/8/12 14:02
 * @Version 1.0
 */

/**
 * @author Sheng Wenzeng
 * @ClassName Car
 * @Description TODO
 * @Date 2019/8/12 14:02
 * @Version 1.0
 */
class Car {
    private String brand;
    private int speed;
    private double price;

    Car(String brand, int speed, double price) {
        this.brand = brand;
        this.speed = speed;
        this.price = price;
    }

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

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public void setSpeed(int speed) {
        this.speed = speed;
    }

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

2. 通过调用实例工厂方法创建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.当客户端需要请求对象时,只需要简单的调用该实例方法而不需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<constructor-args>元素为工厂方法传递方法参数

代码示例:

instanceFactory.java

package factory;/*
 * @Author Sheng WenZeng
 * @Date 2019/8/12 14:19
 * @Version 1.0
 */

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

/**
 * @author Sheng Wenzeng
 * @ClassName InstanceFactory
 * @Description TODO 先需要创建工厂本身,再调用工厂的实例方法来返回Bean的实例
 * @Date 2019/8/12 14:19
 * @Version 1.0
 */
public class InstanceFactory {
    private Map<String, Car> cars = new HashMap<>();

    public InstanceFactory() {
        cars.put("Audi", new Car("Audi", 100, 400000));
        cars.put("Ford", new Car("Ford", 50, 200000));
    }

    public Car getCar(String name) {
        return cars.get(name);
    }
}

Car.java

package factory;/*
 * @Author Sheng WenZeng
 * @Date 2019/8/12 14:02
 * @Version 1.0
 */

/**
 * @author Sheng Wenzeng
 * @ClassName Car
 * @Description TODO
 * @Date 2019/8/12 14:02
 * @Version 1.0
 */
class Car {
    private String brand;
    private int speed;
    private double price;

    Car(String brand, int speed, double price) {
        this.brand = brand;
        this.speed = speed;
        this.price = price;
    }

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

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public void setSpeed(int speed) {
        this.speed = speed;
    }

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

Main.java

package factory;/*
 * @Author Sheng WenZeng
 * @Date 2019/8/12 14:08
 * @Version 1.0
 */

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

/**
 * @author Sheng Wenzeng
 * @ClassName Main
 * @Description TODO
 * @Date 2019/8/12 14:08
 * @Version 1.0
 */
public class Main {
    public static void main(String[] args) {
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("factory/factory.xml");
        Car car1 = (Car) applicationContext.getBean("car1");
        System.out.println(car1);
    }
}

factory.xml

<?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">

    <!--配置工厂的实例-->
    <bean id="instanceFactory" class="factory.InstanceFactory"/>

    <bean id="car1" factory-bean="instanceFactory" factory-method="getCar">
        <constructor-arg value="Ford"/>
    </bean>
</beans>

运行结果:

Car{brand='Ford', speed=50, price=200000.0}